[llvm] r231294 - Update LangRef for getelementptr explicit type changes
David Blaikie
dblaikie at gmail.com
Wed Mar 4 14:02:58 PST 2015
Author: dblaikie
Date: Wed Mar 4 16:02:58 2015
New Revision: 231294
URL: http://llvm.org/viewvc/llvm-project?rev=231294&view=rev
Log:
Update LangRef for getelementptr explicit type changes
Here's a rough/first draft - it at least hits the actual textual IR
examples and some of the phrasing. It's probably worth a full pass over,
but I'm not sure how much these docs should reflect the strange
intermediate state we're in anyway.
Totally open to lots of review/feedback/suggestions.
Modified:
llvm/trunk/docs/GetElementPtr.rst
llvm/trunk/docs/LangRef.rst
Modified: llvm/trunk/docs/GetElementPtr.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/GetElementPtr.rst?rev=231294&r1=231293&r2=231294&view=diff
==============================================================================
--- llvm/trunk/docs/GetElementPtr.rst (original)
+++ llvm/trunk/docs/GetElementPtr.rst Wed Mar 4 16:02:58 2015
@@ -89,12 +89,12 @@ looks like:
void %munge(%struct.munger_struct* %P) {
entry:
- %tmp = getelementptr %struct.munger_struct* %P, i32 1, i32 0
+ %tmp = getelementptr %struct.munger_struct, %struct.munger_struct* %P, i32 1, i32 0
%tmp = load i32* %tmp
- %tmp6 = getelementptr %struct.munger_struct* %P, i32 2, i32 1
+ %tmp6 = getelementptr %struct.munger_struct, %struct.munger_struct* %P, i32 2, i32 1
%tmp7 = load i32* %tmp6
%tmp8 = add i32 %tmp7, %tmp
- %tmp9 = getelementptr %struct.munger_struct* %P, i32 0, i32 0
+ %tmp9 = getelementptr %struct.munger_struct, %struct.munger_struct* %P, i32 0, i32 0
store i32 %tmp8, i32* %tmp9
ret void
}
@@ -109,9 +109,9 @@ To make this clear, let's consider a mor
%MyVar = uninitialized global i32
...
- %idx1 = getelementptr i32* %MyVar, i64 0
- %idx2 = getelementptr i32* %MyVar, i64 1
- %idx3 = getelementptr i32* %MyVar, i64 2
+ %idx1 = getelementptr i32, i32* %MyVar, i64 0
+ %idx2 = getelementptr i32, i32* %MyVar, i64 1
+ %idx3 = getelementptr i32, i32* %MyVar, i64 2
These GEP instructions are simply making address computations from the base
address of ``MyVar``. They compute, as follows (using C syntax):
@@ -146,7 +146,7 @@ variable which is always a pointer type.
%MyStruct = uninitialized global { float*, i32 }
...
- %idx = getelementptr { float*, i32 }* %MyStruct, i64 0, i32 1
+ %idx = getelementptr { float*, i32 }, { float*, i32 }* %MyStruct, i64 0, i32 1
The GEP above yields an ``i32*`` by indexing the ``i32`` typed field of the
structure ``%MyStruct``. When people first look at it, they wonder why the ``i64
@@ -182,7 +182,7 @@ only involved in the computation of addr
%MyVar = uninitialized global { [40 x i32 ]* }
...
- %idx = getelementptr { [40 x i32]* }* %MyVar, i64 0, i32 0, i64 0, i64 17
+ %idx = getelementptr { [40 x i32]* }, { [40 x i32]* }* %MyVar, i64 0, i32 0, i64 0, i64 17
In this example, we have a global variable, ``%MyVar`` that is a pointer to a
structure containing a pointer to an array of 40 ints. The GEP instruction seems
@@ -197,9 +197,9 @@ following:
.. code-block:: llvm
- %idx = getelementptr { [40 x i32]* }* %, i64 0, i32 0
+ %idx = getelementptr { [40 x i32]* }, { [40 x i32]* }* %, i64 0, i32 0
%arr = load [40 x i32]** %idx
- %idx = getelementptr [40 x i32]* %arr, i64 0, i64 17
+ %idx = getelementptr [40 x i32], [40 x i32]* %arr, i64 0, i64 17
In this case, we have to load the pointer in the structure with a load
instruction before we can index into the array. If the example was changed to:
@@ -208,7 +208,7 @@ instruction before we can index into the
%MyVar = uninitialized global { [40 x i32 ] }
...
- %idx = getelementptr { [40 x i32] }*, i64 0, i32 0, i64 17
+ %idx = getelementptr { [40 x i32] }, { [40 x i32] }*, i64 0, i32 0, i64 17
then everything works fine. In this case, the structure does not contain a
pointer and the GEP instruction can index through the global variable, into the
@@ -225,9 +225,9 @@ index. Consider this example:
.. code-block:: llvm
- %MyVar = global { [10 x i32 ] }
- %idx1 = getelementptr { [10 x i32 ] }* %MyVar, i64 0, i32 0, i64 1
- %idx2 = getelementptr { [10 x i32 ] }* %MyVar, i64 1
+ %MyVar = global { [10 x i32] }
+ %idx1 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 0, i32 0, i64 1
+ %idx2 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 1
In this example, ``idx1`` computes the address of the second integer in the
array that is in the structure in ``%MyVar``, that is ``MyVar+4``. The type of
@@ -248,9 +248,9 @@ type. Consider this example:
.. code-block:: llvm
- %MyVar = global { [10 x i32 ] }
- %idx1 = getelementptr { [10 x i32 ] }* %MyVar, i64 1, i32 0, i64 0
- %idx2 = getelementptr { [10 x i32 ] }* %MyVar, i64 1
+ %MyVar = global { [10 x i32] }
+ %idx1 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 1, i32 0, i64 0
+ %idx2 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 1
In this example, the value of ``%idx1`` is ``%MyVar+40`` and its type is
``i32*``. The value of ``%idx2`` is also ``MyVar+40`` but its type is ``{ [10 x
Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=231294&r1=231293&r2=231294&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Wed Mar 4 16:02:58 2015
@@ -162,7 +162,7 @@ symbol table entries. Here is an example
; Definition of main function
define i32 @main() { ; i32()*
; Convert [13 x i8]* to i8 *...
- %cast210 = getelementptr [13 x i8]* @.str, i64 0, i64 0
+ %cast210 = getelementptr [13 x i8], [13 x i8]* @.str, i64 0, i64 0
; Call puts function to write out the string to stdout.
call i32 @puts(i8* %cast210)
@@ -1057,8 +1057,8 @@ The prefix data can be referenced as,
.. code-block:: llvm
- %0 = bitcast *void () @f to *i32
- %a = getelementptr inbounds *i32 %0, i32 -1
+ %0 = bitcast void* () @f to i32*
+ %a = getelementptr inbounds i32, i32* %0, i32 -1
%b = load i32* %a
Prefix data is laid out as if it were an initializer for a global variable
@@ -1584,7 +1584,7 @@ A pointer value is *based* on another po
following rules:
- A pointer value formed from a ``getelementptr`` operation is *based*
- on the first operand of the ``getelementptr``.
+ on the first value operand of the ``getelementptr``.
- The result value of a ``bitcast`` is *based* on the operand of the
``bitcast``.
- A pointer value formed by an ``inttoptr`` is *based* on all pointer
@@ -2567,7 +2567,7 @@ Here are some examples:
entry:
%poison = sub nuw i32 0, 1 ; Results in a poison value.
%still_poison = and i32 %poison, 0 ; 0, but also poison.
- %poison_yet_again = getelementptr i32* @h, i32 %still_poison
+ %poison_yet_again = getelementptr i32, i32* @h, i32 %still_poison
store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
store i32 %poison, i32* @g ; Poison value stored to memory.
@@ -5930,9 +5930,9 @@ Syntax:
::
- <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
- <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
- <result> = getelementptr <ptr vector> ptrval, <vector index type> idx
+ <result> = getelementptr <ty>, <ty>* <ptrval>{, <ty> <idx>}*
+ <result> = getelementptr inbounds <ty>, <ty>* <ptrval>{, <ty> <idx>}*
+ <result> = getelementptr <ty>, <ptr vector> <ptrval>, <vector index type> <idx>
Overview:
"""""""""
@@ -5944,8 +5944,9 @@ address calculation only and does not ac
Arguments:
""""""""""
-The first argument is always a pointer or a vector of pointers, and
-forms the basis of the calculation. The remaining arguments are indices
+The first argument is always a type used as the basis for the calculations.
+The second argument is always a pointer or a vector of pointers, and is the
+base address to start from. The remaining arguments are indices
that indicate which of the elements of the aggregate object are indexed.
The interpretation of each index is dependent on the type being indexed
into. The first index always indexes the pointer value given as the
@@ -5993,7 +5994,7 @@ The LLVM code generated by Clang is:
define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
entry:
- %arrayidx = getelementptr inbounds %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
+ %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
ret i32* %arrayidx
}
@@ -6018,11 +6019,11 @@ for the given testcase is equivalent to:
.. code-block:: llvm
define i32* @foo(%struct.ST* %s) {
- %t1 = getelementptr %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
- %t2 = getelementptr %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
- %t3 = getelementptr %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
- %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
- %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
+ %t1 = getelementptr %struct.ST, %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
+ %t2 = getelementptr %struct.ST, %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
+ %t3 = getelementptr %struct.RT, %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
+ %t4 = getelementptr [10 x [20 x i32]], [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
+ %t5 = getelementptr [20 x i32], [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
ret i32* %t5
}
@@ -6056,20 +6057,20 @@ Example:
.. code-block:: llvm
; yields [12 x i8]*:aptr
- %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
+ %aptr = getelementptr {i32, [12 x i8]}, {i32, [12 x i8]}* %saptr, i64 0, i32 1
; yields i8*:vptr
- %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
+ %vptr = getelementptr {i32, <2 x i8>}, {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
; yields i8*:eptr
- %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
+ %eptr = getelementptr [12 x i8], [12 x i8]* %aptr, i64 0, i32 1
; yields i32*:iptr
- %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
+ %iptr = getelementptr [10 x i32], [10 x i32]* @arr, i16 0, i16 0
In cases where the pointer argument is a vector of pointers, each index
must be a vector with the same number of elements. For example:
.. code-block:: llvm
- %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets,
+ %A = getelementptr i8, <4 x i8*> %ptrs, <4 x i64> %offsets,
Conversion Operations
---------------------
@@ -9546,7 +9547,7 @@ It can be created as follows:
.. code-block:: llvm
%tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
- %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
+ %tramp1 = getelementptr [10 x i8], [10 x i8]* %tramp, i32 0, i32 0
call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
%p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
%fp = bitcast i8* %p to i32 (i32, i32)*
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