[llvm] 4b5618a - [Docs] Cleanup pass documentation
Aiden Grossman via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 10 16:19:06 PDT 2023
Author: Aiden Grossman
Date: 2023-08-10T16:18:56-07:00
New Revision: 4b5618a4b115dca31747f6c1b975ca773cda761f
URL: https://github.com/llvm/llvm-project/commit/4b5618a4b115dca31747f6c1b975ca773cda761f
DIFF: https://github.com/llvm/llvm-project/commit/4b5618a4b115dca31747f6c1b975ca773cda761f.diff
LOG: [Docs] Cleanup pass documentation
Currently the pass documentation specifies every pass with a single dash
(-) in front of it as this was the old format for specifying passes with
opt. However, after the transition to the new PM, this syntax is
deprecated. This patch removes all the single dashes from the pass page
to reflect this. Additionally, some previously removed/renamed passes
are removed/updated in the pass list.
Differential Revision: https://reviews.llvm.org/D157656
Added:
Modified:
llvm/docs/LoopTerminology.rst
llvm/docs/Passes.rst
Removed:
################################################################################
diff --git a/llvm/docs/LoopTerminology.rst b/llvm/docs/LoopTerminology.rst
index 3d3f2573e1403d..995d3e10a0ae35 100644
--- a/llvm/docs/LoopTerminology.rst
+++ b/llvm/docs/LoopTerminology.rst
@@ -373,7 +373,7 @@ PHI nodes in the exit blocks (the alternative would be to
scan the def-use chain [#def-use-chain]_ of all instructions in the loop).
Then, consider for example
-:ref:`-loop-unswitch <passes-loop-unswitch>` ing the loop above.
+:ref:`simple-loop-unswitch <passes-simple-loop-unswitch>` ing the loop above.
Because it is in LCSSA form, we know that any value defined inside of
the loop will be used either only inside the loop or in a loop closing
PHI node. In this case, the only loop closing PHI node is X4.
diff --git a/llvm/docs/Passes.rst b/llvm/docs/Passes.rst
index d555c40ae1d483..461dff21dc4505 100644
--- a/llvm/docs/Passes.rst
+++ b/llvm/docs/Passes.rst
@@ -26,8 +26,8 @@ Analysis Passes
This section describes the LLVM Analysis Passes.
-``-aa-eval``: Exhaustive Alias Analysis Precision Evaluator
------------------------------------------------------------
+``aa-eval``: Exhaustive Alias Analysis Precision Evaluator
+----------------------------------------------------------
This is a simple N^2 alias analysis accuracy evaluator. Basically, for each
function in the program, it simply queries to see how the alias analysis
@@ -37,14 +37,14 @@ function.
This is inspired and adapted from code by: Naveen Neelakantam, Francesco
Spadini, and Wojciech Stryjewski.
-``-basic-aa``: Basic Alias Analysis (stateless AA impl)
--------------------------------------------------------
+``basic-aa``: Basic Alias Analysis (stateless AA impl)
+------------------------------------------------------
A basic alias analysis pass that implements identities (two
diff erent globals
cannot alias, etc), but does no stateful analysis.
-``-basiccg``: Basic CallGraph Construction
-------------------------------------------
+``basiccg``: Basic CallGraph Construction
+-----------------------------------------
Yet to be written.
@@ -56,44 +56,34 @@ the alias analysis implementation being used responds.
.. _passes-da:
-``-da``: Dependence Analysis
-----------------------------
+``da``: Dependence Analysis
+---------------------------
Dependence analysis framework, which is used to detect dependences in memory
accesses.
-``-debug-aa``: AA use debugger
-------------------------------
-
-This simple pass checks alias analysis users to ensure that if they create a
-new value, they do not query AA without informing it of the value. It acts as
-a shim over any other AA pass you want.
-
-Yes keeping track of every value in the program is expensive, but this is a
-debugging pass.
-
-``-domfrontier``: Dominance Frontier Construction
--------------------------------------------------
+``domfrontier``: Dominance Frontier Construction
+------------------------------------------------
This pass is a simple dominator construction algorithm for finding forward
dominator frontiers.
-``-domtree``: Dominator Tree Construction
------------------------------------------
+``domtree``: Dominator Tree Construction
+----------------------------------------
This pass is a simple dominator construction algorithm for finding forward
dominators.
-``-dot-callgraph``: Print Call Graph to "dot" file
---------------------------------------------------
+``dot-callgraph``: Print Call Graph to "dot" file
+-------------------------------------------------
This pass, only available in ``opt``, prints the call graph into a ``.dot``
graph. This graph can then be processed with the "dot" tool to convert it to
postscript or some other suitable format.
-``-dot-cfg``: Print CFG of function to "dot" file
--------------------------------------------------
+``dot-cfg``: Print CFG of function to "dot" file
+------------------------------------------------
This pass, only available in ``opt``, prints the control flow graph into a
``.dot`` graph. This graph can then be processed with the :program:`dot` tool
@@ -102,8 +92,8 @@ Additionally the ``-cfg-func-name=<substring>`` option can be used to filter the
functions that are printed. All functions that contain the specified substring
will be printed.
-``-dot-cfg-only``: Print CFG of function to "dot" file (with no function bodies)
---------------------------------------------------------------------------------
+``dot-cfg-only``: Print CFG of function to "dot" file (with no function bodies)
+-------------------------------------------------------------------------------
This pass, only available in ``opt``, prints the control flow graph into a
``.dot`` graph, omitting the function bodies. This graph can then be processed
@@ -113,75 +103,61 @@ Additionally the ``-cfg-func-name=<substring>`` option can be used to filter the
functions that are printed. All functions that contain the specified substring
will be printed.
-``-dot-dom``: Print dominance tree of function to "dot" file
-------------------------------------------------------------
+``dot-dom``: Print dominance tree of function to "dot" file
+-----------------------------------------------------------
This pass, only available in ``opt``, prints the dominator tree into a ``.dot``
graph. This graph can then be processed with the :program:`dot` tool to
convert it to postscript or some other suitable format.
-``-dot-dom-only``: Print dominance tree of function to "dot" file (with no function bodies)
--------------------------------------------------------------------------------------------
+``dot-dom-only``: Print dominance tree of function to "dot" file (with no function bodies)
+------------------------------------------------------------------------------------------
This pass, only available in ``opt``, prints the dominator tree into a ``.dot``
graph, omitting the function bodies. This graph can then be processed with the
:program:`dot` tool to convert it to postscript or some other suitable format.
-``-dot-post-dom``: Print postdominance tree of function to "dot" file
----------------------------------------------------------------------
+``dot-post-dom``: Print postdominance tree of function to "dot" file
+--------------------------------------------------------------------
This pass, only available in ``opt``, prints the post dominator tree into a
``.dot`` graph. This graph can then be processed with the :program:`dot` tool
to convert it to postscript or some other suitable format.
-``-dot-post-dom-only``: Print postdominance tree of function to "dot" file (with no function bodies)
-----------------------------------------------------------------------------------------------------
+``dot-post-dom-only``: Print postdominance tree of function to "dot" file (with no function bodies)
+---------------------------------------------------------------------------------------------------
This pass, only available in ``opt``, prints the post dominator tree into a
``.dot`` graph, omitting the function bodies. This graph can then be processed
with the :program:`dot` tool to convert it to postscript or some other suitable
format.
-``-globalsmodref-aa``: Simple mod/ref analysis for globals
-----------------------------------------------------------
+``globals-aa``: Simple mod/ref analysis for globals
+---------------------------------------------------
This simple pass provides alias and mod/ref information for global values that
do not have their address taken, and keeps track of whether functions read or
write memory (are "pure"). For this simple (but very common) case, we can
provide pretty accurate and useful information.
-``-instcount``: Counts the various types of ``Instruction``\ s
---------------------------------------------------------------
+``instcount``: Counts the various types of ``Instruction``\ s
+-------------------------------------------------------------
This pass collects the count of all instructions and reports them.
-``-intervals``: Interval Partition Construction
------------------------------------------------
-
-This analysis calculates and represents the interval partition of a function,
-or a preexisting interval partition.
-
-In this way, the interval partition may be used to reduce a flow graph down to
-its degenerate single node interval partition (unless it is irreducible).
-
-``-iv-users``: Induction Variable Users
----------------------------------------
+``iv-users``: Induction Variable Users
+--------------------------------------
Bookkeeping for "interesting" users of expressions computed from induction
variables.
-``-lazy-value-info``: Lazy Value Information Analysis
------------------------------------------------------
+``lazy-value-info``: Lazy Value Information Analysis
+----------------------------------------------------
Interface for lazy computation of value constraint information.
-``-libcall-aa``: LibCall Alias Analysis
----------------------------------------
-
-LibCall Alias Analysis.
-
-``-lint``: Statically lint-checks LLVM IR
------------------------------------------
+``lint``: Statically lint-checks LLVM IR
+----------------------------------------
This pass statically checks for common and easily-identified constructs which
produce undefined or likely unintended behavior in LLVM IR.
@@ -207,24 +183,24 @@ cases, instcombine checks for the same kinds of things and turns instructions
with undefined behavior into unreachable (or equivalent). Because of this,
this pass makes some effort to look through bitcasts and so on.
-``-loops``: Natural Loop Information
-------------------------------------
+``loops``: Natural Loop Information
+-----------------------------------
This analysis is used to identify natural loops and determine the loop depth of
various nodes of the CFG. Note that the loops identified may actually be
several natural loops that share the same header node... not just a single
natural loop.
-``-memdep``: Memory Dependence Analysis
----------------------------------------
+``memdep``: Memory Dependence Analysis
+--------------------------------------
An analysis that determines, for a given memory operation, what preceding
memory operations it depends on. It builds on alias analysis information, and
tries to provide a lazy, caching interface to a common kind of alias
information query.
-``-module-debuginfo``: Decodes module-level debug info
-------------------------------------------------------
+``module-debuginfo``: Decodes module-level debug info
+-----------------------------------------------------
This pass decodes the debug info metadata in a module and prints in a
(sufficiently-prepared-) human-readable form.
@@ -232,64 +208,49 @@ This pass decodes the debug info metadata in a module and prints in a
For example, run this pass from ``opt`` along with the ``-analyze`` option, and
it'll print to standard output.
-``-postdomfrontier``: Post-Dominance Frontier Construction
-----------------------------------------------------------
-
-This pass is a simple post-dominator construction algorithm for finding
-post-dominator frontiers.
-
-``-postdomtree``: Post-Dominator Tree Construction
---------------------------------------------------
+``postdomtree``: Post-Dominator Tree Construction
+-------------------------------------------------
This pass is a simple post-dominator construction algorithm for finding
post-dominators.
-``-print-alias-sets``: Alias Set Printer
-----------------------------------------
+``print-alias-sets``: Alias Set Printer
+---------------------------------------
Yet to be written.
-``-print-callgraph``: Print a call graph
-----------------------------------------
+``print-callgraph``: Print a call graph
+---------------------------------------
This pass, only available in ``opt``, prints the call graph to standard error
in a human-readable form.
-``-print-callgraph-sccs``: Print SCCs of the Call Graph
--------------------------------------------------------
+``print-callgraph-sccs``: Print SCCs of the Call Graph
+------------------------------------------------------
This pass, only available in ``opt``, prints the SCCs of the call graph to
standard error in a human-readable form.
-``-print-cfg-sccs``: Print SCCs of each function CFG
-----------------------------------------------------
+``print-cfg-sccs``: Print SCCs of each function CFG
+---------------------------------------------------
This pass, only available in ``opt``, printsthe SCCs of each function CFG to
standard error in a human-readable fom.
-``-print-function``: Print function to stderr
----------------------------------------------
+``print-function``: Print function to stderr
+--------------------------------------------
The ``PrintFunctionPass`` class is designed to be pipelined with other
``FunctionPasses``, and prints out the functions of the module as they are
processed.
-``-print-module``: Print module to stderr
------------------------------------------
+``print-module``: Print module to stderr
+----------------------------------------
This pass simply prints out the entire module when it is executed.
-.. _passes-print-used-types:
-
-``-print-used-types``: Find Used Types
---------------------------------------
-
-This pass is used to seek out all of the types in use by the program. Note
-that this analysis explicitly does not include types only used by the symbol
-table.
-
-``-regions``: Detect single entry single exit regions
------------------------------------------------------
+``regions``: Detect single entry single exit regions
+----------------------------------------------------
The ``RegionInfo`` pass detects single entry single exit regions in a function,
where a region is defined as any subgraph that is connected to the remaining
@@ -297,8 +258,8 @@ graph at only two spots. Furthermore, a hierarchical region tree is built.
.. _passes-scalar-evolution:
-``-scalar-evolution``: Scalar Evolution Analysis
-------------------------------------------------
+``scalar-evolution``: Scalar Evolution Analysis
+-----------------------------------------------
The ``ScalarEvolution`` analysis can be used to analyze and categorize scalar
expressions in loops. It specializes in recognizing general induction
@@ -309,8 +270,8 @@ obtained.
This analysis is primarily useful for induction variable substitution and
strength reduction.
-``-scev-aa``: ScalarEvolution-based Alias Analysis
---------------------------------------------------
+``scev-aa``: ScalarEvolution-based Alias Analysis
+-------------------------------------------------
Simple alias analysis implemented in terms of ``ScalarEvolution`` queries.
@@ -321,8 +282,8 @@ between
diff erent iterations.
``ScalarEvolution`` has a more complete understanding of pointer arithmetic
than ``BasicAliasAnalysis``' collection of ad-hoc analyses.
-``-stack-safety``: Stack Safety Analysis
-------------------------------------------------
+``stack-safety``: Stack Safety Analysis
+---------------------------------------
The ``StackSafety`` analysis can be used to determine if stack allocated
variables can be considered safe from memory access bugs.
@@ -330,33 +291,27 @@ variables can be considered safe from memory access bugs.
This analysis' primary purpose is to be used by sanitizers to avoid unnecessary
instrumentation of safe variables.
-``-targetdata``: Target Data Layout
------------------------------------
-
-Provides other passes access to information on how the size and alignment
-required by the target ABI for various data types.
-
Transform Passes
================
This section describes the LLVM Transform Passes.
-``-adce``: Aggressive Dead Code Elimination
--------------------------------------------
+``adce``: Aggressive Dead Code Elimination
+------------------------------------------
ADCE aggressively tries to eliminate code. This pass is similar to :ref:`DCE
<passes-dce>` but it assumes that values are dead until proven otherwise. This
is similar to :ref:`SCCP <passes-sccp>`, except applied to the liveness of
values.
-``-always-inline``: Inliner for ``always_inline`` functions
------------------------------------------------------------
+``always-inline``: Inliner for ``always_inline`` functions
+----------------------------------------------------------
A custom inliner that handles only functions that are marked as "always
inline".
-``-argpromotion``: Promote 'by reference' arguments to scalars
---------------------------------------------------------------
+``argpromotion``: Promote 'by reference' arguments to scalars
+-------------------------------------------------------------
This pass promotes "by reference" arguments to be "by value" arguments. In
practice, this means looking for internal functions that have pointer
@@ -377,23 +332,8 @@ stored to (returning the value instead), but does not currently. This case
would be best handled when and if LLVM starts supporting multiple return values
from functions.
-``-bb-vectorize``: Basic-Block Vectorization
---------------------------------------------
-
-This pass combines instructions inside basic blocks to form vector
-instructions. It iterates over each basic block, attempting to pair compatible
-instructions, repeating this process until no additional pairs are selected for
-vectorization. When the outputs of some pair of compatible instructions are
-used as inputs by some other pair of compatible instructions, those pairs are
-part of a potential vectorization chain. Instruction pairs are only fused into
-vector instructions when they are part of a chain longer than some threshold
-length. Moreover, the pass attempts to find the best possible chain for each
-pair of compatible instructions. These heuristics are intended to prevent
-vectorization in cases where it would not yield a performance increase of the
-resulting code.
-
-``-block-placement``: Profile Guided Basic Block Placement
-----------------------------------------------------------
+``block-placement``: Profile Guided Basic Block Placement
+---------------------------------------------------------
This pass is a very simple profile guided basic block placement algorithm. The
idea is to put frequently executed blocks together at the start of the function
@@ -401,23 +341,23 @@ and hopefully increase the number of fall-through conditional branches. If
there is no profile information for a particular function, this pass basically
orders blocks in depth-first order.
-``-break-crit-edges``: Break critical edges in CFG
---------------------------------------------------
+``break-crit-edges``: Break critical edges in CFG
+-------------------------------------------------
Break all of the critical edges in the CFG by inserting a dummy basic block.
It may be "required" by passes that cannot deal with critical edges. This
transformation obviously invalidates the CFG, but can update forward dominator
(set, immediate dominators, tree, and frontier) information.
-``-codegenprepare``: Optimize for code generation
--------------------------------------------------
+``codegenprepare``: Optimize for code generation
+------------------------------------------------
This pass munges the code in the input function to better prepare it for
SelectionDAG-based code generation. This works around limitations in its
basic-block-at-a-time approach. It should eventually be removed.
-``-constmerge``: Merge Duplicate Global Constants
--------------------------------------------------
+``constmerge``: Merge Duplicate Global Constants
+------------------------------------------------
Merges duplicate global constants together into a single constant that is
shared. This is useful because some passes (i.e., TraceValues) insert a lot of
@@ -426,15 +366,15 @@ string is available.
.. _passes-dce:
-``-dce``: Dead Code Elimination
--------------------------------
+``dce``: Dead Code Elimination
+------------------------------
-Dead code elimination is similar to :ref:`dead instruction elimination
-<passes-die>`, but it rechecks instructions that were used by removed
-instructions to see if they are newly dead.
+Dead code elimination is similar to dead instruction elimination, but it
+rechecks instructions that were used by removed instructions to see if they
+are newly dead.
-``-deadargelim``: Dead Argument Elimination
--------------------------------------------
+``deadargelim``: Dead Argument Elimination
+------------------------------------------
This pass deletes dead arguments from internal functions. Dead argument
elimination removes arguments which are directly dead, as well as arguments
@@ -444,31 +384,16 @@ pass also deletes dead arguments in a similar way.
This pass is often useful as a cleanup pass to run after aggressive
interprocedural passes, which add possibly-dead arguments.
-``-deadtypeelim``: Dead Type Elimination
-----------------------------------------
-
-This pass is used to cleanup the output of GCC. It eliminate names for types
-that are unused in the entire translation unit, using the :ref:`find used types
-<passes-print-used-types>` pass.
-
-.. _passes-die:
-
-``-die``: Dead Instruction Elimination
---------------------------------------
-
-Dead instruction elimination performs a single pass over the function, removing
-instructions that are obviously dead.
-
-``-dse``: Dead Store Elimination
---------------------------------
+``dse``: Dead Store Elimination
+-------------------------------
A trivial dead store elimination that only considers basic-block local
redundant stores.
.. _passes-function-attrs:
-``-function-attrs``: Deduce function attributes
------------------------------------------------
+``function-attrs``: Deduce function attributes
+----------------------------------------------
A simple interprocedural pass which walks the call-graph, looking for functions
which do not access or only read non-local memory, and marking them
@@ -479,8 +404,8 @@ that the pointer is only dereferenced, and not returned from the function or
stored in a global. This pass is implemented as a bottom-up traversal of the
call-graph.
-``-globaldce``: Dead Global Elimination
----------------------------------------
+``globaldce``: Dead Global Elimination
+--------------------------------------
This transform is designed to eliminate unreachable internal globals from the
program. It uses an aggressive algorithm, searching out globals that are known
@@ -488,23 +413,23 @@ to be alive. After it finds all of the globals which are needed, it deletes
whatever is left over. This allows it to delete recursive chunks of the
program which are unreachable.
-``-globalopt``: Global Variable Optimizer
------------------------------------------
+``globalopt``: Global Variable Optimizer
+----------------------------------------
This pass transforms simple global variables that never have their address
taken. If obviously true, it marks read/write globals as constant, deletes
variables only stored to, etc.
-``-gvn``: Global Value Numbering
---------------------------------
+``gvn``: Global Value Numbering
+-------------------------------
This pass performs global value numbering to eliminate fully and partially
redundant instructions. It also performs redundant load elimination.
.. _passes-indvars:
-``-indvars``: Canonicalize Induction Variables
-----------------------------------------------
+``indvars``: Canonicalize Induction Variables
+---------------------------------------------
This transformation analyzes and transforms the induction variables (and
computations derived from them) into simpler forms suitable for subsequent
@@ -546,15 +471,15 @@ desired loop transformations have been performed. Additionally, on targets
where it is profitable, the loop could be transformed to count down to zero
(the "do loop" optimization).
-``-inline``: Function Integration/Inlining
-------------------------------------------
+``inline``: Function Integration/Inlining
+-----------------------------------------
Bottom-up inlining of functions into callees.
.. _passes-instcombine:
-``-instcombine``: Combine redundant instructions
-------------------------------------------------
+``instcombine``: Combine redundant instructions
+-----------------------------------------------
Combine instructions to form fewer, simple instructions. This pass does not
modify the CFG. This pass is where algebraic simplification happens.
@@ -599,7 +524,7 @@ library calls on
diff erent targets.
.. _passes-aggressive-instcombine:
-``-aggressive-instcombine``: Combine expression patterns
+``aggressive-instcombine``: Combine expression patterns
--------------------------------------------------------
Combine expression patterns to form expressions with fewer, simple instructions.
@@ -611,21 +536,21 @@ It
diff ers from instcombine pass in that it can modify CFG and contains pattern
optimization that requires higher complexity than the O(1), thus, it should run fewer
times than instcombine pass.
-``-internalize``: Internalize Global Symbols
---------------------------------------------
+``internalize``: Internalize Global Symbols
+-------------------------------------------
This pass loops over all of the functions in the input module, looking for a
main function. If a main function is found, all other functions and all global
variables with initializers are marked as internal.
-``-ipsccp``: Interprocedural Sparse Conditional Constant Propagation
---------------------------------------------------------------------
+``ipsccp``: Interprocedural Sparse Conditional Constant Propagation
+-------------------------------------------------------------------
An interprocedural variant of :ref:`Sparse Conditional Constant Propagation
<passes-sccp>`.
-``-jump-threading``: Jump Threading
------------------------------------
+``jump-threading``: Jump Threading
+----------------------------------
Jump threading tries to find distinct threads of control flow running through a
basic block. This pass looks at blocks that have multiple predecessors and
@@ -648,8 +573,8 @@ revectored to the false side of the second if.
.. _passes-lcssa:
-``-lcssa``: Loop-Closed SSA Form Pass
--------------------------------------
+``lcssa``: Loop-Closed SSA Form Pass
+------------------------------------
This pass transforms loops by placing phi nodes at the end of the loops for all
values that are live across the loop boundary. For example, it turns the left
@@ -674,8 +599,8 @@ transformation is that it makes many other loop optimizations, such as
.. _passes-licm:
-``-licm``: Loop Invariant Code Motion
--------------------------------------
+``licm``: Loop Invariant Code Motion
+------------------------------------
This pass performs loop invariant code motion, attempting to remove as much
code from the body of a loop as possible. It does this by either hoisting code
@@ -708,8 +633,8 @@ This pass uses alias analysis for two purposes:
:ref:`mem2reg <passes-mem2reg>` functionality to construct the appropriate
SSA form for the variable.
-``-loop-deletion``: Delete dead loops
--------------------------------------
+``loop-deletion``: Delete dead loops
+------------------------------------
This file implements the Dead Loop Deletion Pass. This pass is responsible for
eliminating loops with non-infinite computable trip counts that have no side
@@ -718,23 +643,16 @@ the function's return value.
.. _passes-loop-extract:
-``-loop-extract``: Extract loops into new functions
----------------------------------------------------
+``loop-extract``: Extract loops into new functions
+--------------------------------------------------
A pass wrapper around the ``ExtractLoop()`` scalar transformation to extract
each top-level loop into its own new function. If the loop is the *only* loop
in a given function, it is not touched. This is a pass most useful for
debugging via bugpoint.
-``-loop-extract-single``: Extract at most one loop into a new function
-----------------------------------------------------------------------
-
-Similar to :ref:`Extract loops into new functions <passes-loop-extract>`, this
-pass extracts one natural loop from the program into a function if it can.
-This is used by :program:`bugpoint`.
-
-``-loop-reduce``: Loop Strength Reduction
------------------------------------------
+``loop-reduce``: Loop Strength Reduction
+----------------------------------------
This pass performs a strength reduction on array references inside loops that
have as one or more of their components the loop induction variable. This is
@@ -744,8 +662,8 @@ loop to increment the value by the appropriate amount.
.. _passes-loop-rotate:
-``-loop-rotate``: Rotate Loops
-------------------------------
+``loop-rotate``: Rotate Loops
+-----------------------------
A simple loop rotation transformation. A summary of it can be found in
:ref:`Loop Terminology for Rotated Loops <loop-terminology-loop-rotate>`.
@@ -753,8 +671,8 @@ A simple loop rotation transformation. A summary of it can be found in
.. _passes-loop-simplify:
-``-loop-simplify``: Canonicalize natural loops
-----------------------------------------------
+``loop-simplify``: Canonicalize natural loops
+---------------------------------------------
This pass performs several transformations to transform natural loops into a
simpler form, which makes subsequent analyses and transformations simpler and
@@ -780,15 +698,15 @@ not pessimize generated code.
This pass obviously modifies the CFG, but updates loop information and
dominator information.
-``-loop-unroll``: Unroll loops
-------------------------------
+``loop-unroll``: Unroll loops
+-----------------------------
This pass implements a simple loop unroller. It works best when loops have
been canonicalized by the :ref:`indvars <passes-indvars>` pass, allowing it to
determine the trip counts of loops easily.
-``-loop-unroll-and-jam``: Unroll and Jam loops
-----------------------------------------------
+``loop-unroll-and-jam``: Unroll and Jam loops
+---------------------------------------------
This pass implements a simple unroll and jam classical loop optimisation pass.
It transforms loop from:
@@ -808,41 +726,16 @@ loops into one. When variables or loads can be shared in the new inner loop, thi
can lead to significant performance improvements. It uses
:ref:`Dependence Analysis <passes-da>` for proving the transformations are safe.
-.. _passes-loop-unswitch:
-
-``-loop-unswitch``: Unswitch loops
-----------------------------------
-
-This pass transforms loops that contain branches on loop-invariant conditions
-to have multiple loops. For example, it turns the left into the right code:
-
-.. code-block:: c++
-
- for (...) if (lic)
- A for (...)
- if (lic) A; B; C
- B else
- C for (...)
- A; C
-
-This can increase the size of the code exponentially (doubling it every time a
-loop is unswitched) so we only unswitch if the resultant code will be smaller
-than a threshold.
-
-This pass expects :ref:`LICM <passes-licm>` to be run before it to hoist
-invariant conditions out of the loop, to make the unswitching opportunity
-obvious.
-
-``-lower-global-dtors``: Lower global destructors
-------------------------------------------------------------
+``lower-global-dtors``: Lower global destructors
+------------------------------------------------
This pass lowers global module destructors (``llvm.global_dtors``) by creating
wrapper functions that are registered as global constructors in
``llvm.global_ctors`` and which contain a call to ``__cxa_atexit`` to register
their destructor functions.
-``-loweratomic``: Lower atomic intrinsics to non-atomic form
-------------------------------------------------------------
+``loweratomic``: Lower atomic intrinsics to non-atomic form
+-----------------------------------------------------------
This pass lowers atomic intrinsics to non-atomic form for use in a known
non-preemptible environment.
@@ -852,8 +745,8 @@ this would require knowledge of the entire call graph of the program including
any libraries which may not be available in bitcode form); it simply lowers
every atomic intrinsic.
-``-lowerinvoke``: Lower invokes to calls, for unwindless code generators
-------------------------------------------------------------------------
+``lowerinvoke``: Lower invokes to calls, for unwindless code generators
+-----------------------------------------------------------------------
This transformation is designed for use by code generators which do not yet
support stack unwinding. This pass converts ``invoke`` instructions to
@@ -861,8 +754,8 @@ support stack unwinding. This pass converts ``invoke`` instructions to
become dead code (which can be removed by running the ``-simplifycfg`` pass
afterwards).
-``-lowerswitch``: Lower ``SwitchInst``\ s to branches
------------------------------------------------------
+``lowerswitch``: Lower ``SwitchInst``\ s to branches
+----------------------------------------------------
Rewrites switch instructions with a sequence of branches, which allows targets
to get away with not implementing the switch instruction until it is
@@ -870,8 +763,8 @@ convenient.
.. _passes-mem2reg:
-``-mem2reg``: Promote Memory to Register
-----------------------------------------
+``mem2reg``: Promote Memory to Register
+---------------------------------------
This file promotes memory references to be register references. It promotes
alloca instructions which only have loads and stores as uses. An ``alloca`` is
@@ -880,14 +773,14 @@ the function in depth-first order to rewrite loads and stores as appropriate.
This is just the standard SSA construction algorithm to construct "pruned" SSA
form.
-``-memcpyopt``: MemCpy Optimization
------------------------------------
+``memcpyopt``: MemCpy Optimization
+----------------------------------
This pass performs various transformations related to eliminating ``memcpy``
calls, or transforming sets of stores into ``memset``\ s.
-``-mergefunc``: Merge Functions
--------------------------------
+``mergefunc``: Merge Functions
+------------------------------
This pass looks for equivalent functions that are mergeable and folds them.
@@ -910,28 +803,20 @@ Read
:doc:`this <MergeFunctions>`
article for more details.
-``-mergereturn``: Unify function exit nodes
--------------------------------------------
+``mergereturn``: Unify function exit nodes
+------------------------------------------
Ensure that functions have at most one ``ret`` instruction in them.
Additionally, it keeps track of which node is the new exit node of the CFG.
-``-partial-inliner``: Partial Inliner
--------------------------------------
+``partial-inliner``: Partial Inliner
+------------------------------------
This pass performs partial inlining, typically by inlining an ``if`` statement
that surrounds the body of the function.
-``-prune-eh``: Remove unused exception handling info
-----------------------------------------------------
-
-This file implements a simple interprocedural pass which walks the call-graph,
-turning invoke instructions into call instructions if and only if the callee
-cannot throw an exception. It implements this as a bottom-up traversal of the
-call-graph.
-
-``-reassociate``: Reassociate expressions
------------------------------------------
+``reassociate``: Reassociate expressions
+----------------------------------------
This pass reassociates commutative expressions in an order that is designed to
promote better constant propagation, GCSE, :ref:`LICM <passes-licm>`, PRE, etc.
@@ -944,13 +829,13 @@ corresponding to the reverse post order traversal of current function (starting
at 2), which effectively gives values in deep loops higher rank than values not
in loops.
-``-rel-lookup-table-converter``: Relative lookup table converter
-----------------------------------------------------------------
+``rel-lookup-table-converter``: Relative lookup table converter
+---------------------------------------------------------------
This pass converts lookup tables to PIC-friendly relative lookup tables.
-``-reg2mem``: Demote all values to stack slots
-----------------------------------------------
+``reg2mem``: Demote all values to stack slots
+---------------------------------------------
This file demotes all registers to memory references. It is intended to be the
inverse of :ref:`mem2reg <passes-mem2reg>`. By converting to ``load``
@@ -960,8 +845,8 @@ that this should make CFG hacking much easier. To make later hacking easier,
the entry block is split into two, such that all introduced ``alloca``
instructions (and nothing else) are in the entry block.
-``-sroa``: Scalar Replacement of Aggregates
-------------------------------------------------------
+``sroa``: Scalar Replacement of Aggregates
+------------------------------------------
The well-known scalar replacement of aggregates transformation. This transform
breaks up ``alloca`` instructions of aggregate type (structure or array) into
@@ -971,8 +856,8 @@ scalar SSA form.
.. _passes-sccp:
-``-sccp``: Sparse Conditional Constant Propagation
---------------------------------------------------
+``sccp``: Sparse Conditional Constant Propagation
+-------------------------------------------------
Sparse conditional constant propagation and merging, which can be summarized
as:
@@ -987,8 +872,8 @@ idea to run a :ref:`DCE <passes-dce>` pass sometime after running this pass.
.. _passes-simplifycfg:
-``-simplifycfg``: Simplify the CFG
-----------------------------------
+``simplifycfg``: Simplify the CFG
+---------------------------------
Performs dead code elimination and basic block merging. Specifically:
@@ -998,14 +883,39 @@ Performs dead code elimination and basic block merging. Specifically:
* Eliminates PHI nodes for basic blocks with a single predecessor.
* Eliminates a basic block that only contains an unconditional branch.
-``-sink``: Code sinking
------------------------
+``sink``: Code sinking
+----------------------
This pass moves instructions into successor blocks, when possible, so that they
aren't executed on paths where their results aren't needed.
-``-strip``: Strip all symbols from a module
--------------------------------------------
+.. _passes-simple-loop-unswitch:
+
+``simple-loop-unswitch``: Unswitch loops
+----------------------------------------
+
+This pass transforms loops that contain branches on loop-invariant conditions
+to have multiple loops. For example, it turns the left into the right code:
+
+.. code-block:: c++
+
+ for (...) if (lic)
+ A for (...)
+ if (lic) A; B; C
+ B else
+ C for (...)
+ A; C
+
+This can increase the size of the code exponentially (doubling it every time a
+loop is unswitched) so we only unswitch if the resultant code will be smaller
+than a threshold.
+
+This pass expects :ref:`LICM <passes-licm>` to be run before it to hoist
+invariant conditions out of the loop, to make the unswitching opportunity
+obvious.
+
+``strip``: Strip all symbols from a module
+------------------------------------------
Performs code stripping. This transformation can delete:
@@ -1017,8 +927,8 @@ Note that this transformation makes code much less readable, so it should only
be used in situations where the strip utility would be used, such as reducing
code size or making it harder to reverse engineer code.
-``-strip-dead-debug-info``: Strip debug info for unused symbols
----------------------------------------------------------------
+``strip-dead-debug-info``: Strip debug info for unused symbols
+--------------------------------------------------------------
.. FIXME: this description is the same as for -strip
@@ -1032,16 +942,16 @@ note that this transformation makes code much less readable, so it should only
be used in situations where the strip utility would be used, such as reducing
code size or making it harder to reverse engineer code.
-``-strip-dead-prototypes``: Strip Unused Function Prototypes
-------------------------------------------------------------
+``strip-dead-prototypes``: Strip Unused Function Prototypes
+-----------------------------------------------------------
This pass loops over all of the functions in the input module, looking for dead
declarations and removes them. Dead declarations are declarations of functions
for which no implementation is available (i.e., declarations for unused library
functions).
-``-strip-debug-declare``: Strip all ``llvm.dbg.declare`` intrinsics
--------------------------------------------------------------------
+``strip-debug-declare``: Strip all ``llvm.dbg.declare`` intrinsics
+------------------------------------------------------------------
.. FIXME: this description is the same as for -strip
@@ -1055,8 +965,8 @@ Note that this transformation makes code much less readable, so it should only
be used in situations where the 'strip' utility would be used, such as reducing
code size or making it harder to reverse engineer code.
-``-strip-nondebug``: Strip all symbols, except dbg symbols, from a module
--------------------------------------------------------------------------
+``strip-nondebug``: Strip all symbols, except dbg symbols, from a module
+------------------------------------------------------------------------
.. FIXME: this description is the same as for -strip
@@ -1070,8 +980,8 @@ Note that this transformation makes code much less readable, so it should only
be used in situations where the 'strip' utility would be used, such as reducing
code size or making it harder to reverse engineer code.
-``-tailcallelim``: Tail Call Elimination
-----------------------------------------
+``tailcallelim``: Tail Call Elimination
+---------------------------------------
This file transforms calls of the current function (self recursion) followed by
a return instruction with a branch to the entry of the function, creating a
@@ -1098,20 +1008,20 @@ Utility Passes
This section describes the LLVM Utility Passes.
-``-deadarghaX0r``: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)
-------------------------------------------------------------------------
+``deadarghaX0r``: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)
+-----------------------------------------------------------------------
Same as dead argument elimination, but deletes arguments to functions which are
external. This is only for use by :doc:`bugpoint <Bugpoint>`.
-``-extract-blocks``: Extract Basic Blocks From Module (for bugpoint use)
-------------------------------------------------------------------------
+``extract-blocks``: Extract Basic Blocks From Module (for bugpoint use)
+-----------------------------------------------------------------------
This pass is used by bugpoint to extract all blocks from the module into their
own functions.
-``-instnamer``: Assign names to anonymous instructions
-------------------------------------------------------
+``instnamer``: Assign names to anonymous instructions
+-----------------------------------------------------
This is a little utility pass that gives instructions names, this is mostly
useful when
diff ing the effect of an optimization because deleting an unnamed
@@ -1120,8 +1030,8 @@ noisy.
.. _passes-verify:
-``-verify``: Module Verifier
-----------------------------
+``verify``: Module Verifier
+---------------------------
Verifies an LLVM IR code. This is useful to run after an optimization which is
undergoing testing. Note that llvm-as verifies its input before emitting
@@ -1159,16 +1069,16 @@ instead just tries to ensure that code is well-formed.
.. _passes-view-cfg:
-``-view-cfg``: View CFG of function
------------------------------------
+``view-cfg``: View CFG of function
+----------------------------------
Displays the control flow graph using the GraphViz tool.
Additionally the ``-cfg-func-name=<substring>`` option can be used to filter the
functions that are displayed. All functions that contain the specified substring
will be displayed.
-``-view-cfg-only``: View CFG of function (with no function bodies)
-------------------------------------------------------------------
+``view-cfg-only``: View CFG of function (with no function bodies)
+-----------------------------------------------------------------
Displays the control flow graph using the GraphViz tool, but omitting function
bodies.
@@ -1176,30 +1086,30 @@ Additionally the ``-cfg-func-name=<substring>`` option can be used to filter the
functions that are displayed. All functions that contain the specified substring
will be displayed.
-``-view-dom``: View dominance tree of function
-----------------------------------------------
+``view-dom``: View dominance tree of function
+---------------------------------------------
Displays the dominator tree using the GraphViz tool.
-``-view-dom-only``: View dominance tree of function (with no function bodies)
------------------------------------------------------------------------------
+``view-dom-only``: View dominance tree of function (with no function bodies)
+----------------------------------------------------------------------------
Displays the dominator tree using the GraphViz tool, but omitting function
bodies.
-``-view-postdom``: View postdominance tree of function
+``view-post-dom``: View postdominance tree of function
------------------------------------------------------
Displays the post dominator tree using the GraphViz tool.
-``-view-postdom-only``: View postdominance tree of function (with no function bodies)
+``view-post-dom-only``: View postdominance tree of function (with no function bodies)
-------------------------------------------------------------------------------------
Displays the post dominator tree using the GraphViz tool, but omitting function
bodies.
-``-transform-warning``: Report missed forced transformations
-------------------------------------------------------------
+``transform-warning``: Report missed forced transformations
+-----------------------------------------------------------
Emits warnings about not yet applied forced transformations (e.g. from
``#pragma omp simd``).
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