[llvm] r368296 - Add llvm.licm.disable metadata
Tim Corringham via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 8 06:46:17 PDT 2019
Author: timcorringham
Date: Thu Aug 8 06:46:17 2019
New Revision: 368296
URL: http://llvm.org/viewvc/llvm-project?rev=368296&view=rev
Log:
Add llvm.licm.disable metadata
For some targets the LICM pass can result in sub-optimal code in some
cases where it would be better not to run the pass, but it isn't
always possible to suppress the transformations heuristically.
Where the front-end has insight into such cases it is beneficial
to attach loop metadata to disable the pass - this change adds the
llvm.licm.disable metadata to enable that.
Differential Revision: https://reviews.llvm.org/D64557
Added:
llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll
Modified:
llvm/trunk/docs/LangRef.rst
llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
llvm/trunk/lib/Transforms/Scalar/LICM.cpp
llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=368296&r1=368295&r2=368296&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Thu Aug 8 06:46:17 2019
@@ -5381,7 +5381,7 @@ suggests an unroll factor to the loop un
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This metadata disables all optional loop transformations unless
-explicitly instructed using other transformation metdata such as
+explicitly instructed using other transformation metadata such as
``llvm.loop.unroll.enable``. That is, no heuristic will try to determine
whether a transformation is profitable. The purpose is to avoid that the
loop is transformed to a different loop before an explicitly requested
@@ -5720,10 +5720,24 @@ the non-distributed fallback version wil
'``llvm.loop.distribute.followup_all``' Metadata
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-Thes attributes in this metdata is added to all followup loops of the
+The attributes in this metadata is added to all followup loops of the
loop distribution pass. See
:ref:`Transformation Metadata <transformation-metadata>` for details.
+'``llvm.licm.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata indicates that loop-invariant code motion (LICM) should not be
+performed on this loop. The metadata has a single operand which is the string
+``llvm.licm.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.licm.disable"}
+
+Note that although it operates per loop it isn't given the llvm.loop prefix
+as it is not affected by the ``llvm.loop.disable_nonforced`` metadata.
+
'``llvm.access.group``' Metadata
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Modified: llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h?rev=368296&r1=368295&r2=368296&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h (original)
+++ llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h Thu Aug 8 06:46:17 2019
@@ -215,6 +215,9 @@ makeFollowupLoopID(MDNode *OrigLoopID, A
/// Look for the loop attribute that disables all transformation heuristic.
bool hasDisableAllTransformsHint(const Loop *L);
+/// Look for the loop attribute that disables the LICM transformation heuristics.
+bool hasDisableLICMTransformsHint(const Loop *L);
+
/// The mode sets how eager a transformation should be applied.
enum TransformationMode {
/// The pass can use heuristics to determine whether a transformation should
Modified: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LICM.cpp?rev=368296&r1=368295&r2=368296&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp Thu Aug 8 06:46:17 2019
@@ -330,6 +330,12 @@ bool LoopInvariantCodeMotion::runOnLoop(
assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
+ // If this loop has metadata indicating that LICM is not to be performed then
+ // just exit.
+ if (hasDisableLICMTransformsHint(L)) {
+ return false;
+ }
+
std::unique_ptr<AliasSetTracker> CurAST;
std::unique_ptr<MemorySSAUpdater> MSSAU;
bool NoOfMemAccTooLarge = false;
Modified: llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp?rev=368296&r1=368295&r2=368296&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp Thu Aug 8 06:46:17 2019
@@ -45,6 +45,7 @@ using namespace llvm::PatternMatch;
#define DEBUG_TYPE "loop-utils"
static const char *LLVMLoopDisableNonforced = "llvm.loop.disable_nonforced";
+static const char *LLVMLoopDisableLICM = "llvm.licm.disable";
bool llvm::formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
@@ -379,6 +380,10 @@ bool llvm::hasDisableAllTransformsHint(c
return getBooleanLoopAttribute(L, LLVMLoopDisableNonforced);
}
+bool llvm::hasDisableLICMTransformsHint(const Loop *L) {
+ return getBooleanLoopAttribute(L, LLVMLoopDisableLICM);
+}
+
TransformationMode llvm::hasUnrollTransformation(Loop *L) {
if (getBooleanLoopAttribute(L, "llvm.loop.unroll.disable"))
return TM_SuppressedByUser;
Added: llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll?rev=368296&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll (added)
+++ llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll Thu Aug 8 06:46:17 2019
@@ -0,0 +1,33 @@
+; RUN: opt < %s -S -basicaa -licm | FileCheck %s
+
+; Check that the LICM pass does not operate on a loop which has the
+; llvm.licm.disable metadata.
+; CHECK-LABEL: @licm_disable
+; CHECK: entry:
+; CHECK-NOT: load
+; CHECK: do.body:
+; CHECK: load i64, i64* bitcast (i32** @in to i64*)
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+ at in = internal unnamed_addr global i32* null, align 8
+ at out = internal unnamed_addr global i32* null, align 8
+
+define void @licm_disable(i32 %N) {
+entry:
+ br label %do.body
+
+do.body: ; preds = %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
+ %v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
+ store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
+ %inc = add nsw i32 %i.0, 1
+ %cmp = icmp slt i32 %inc, %N
+ br i1 %cmp, label %do.body, label %do.end, !llvm.loop !1
+
+do.end: ; preds = %do.body
+ ret void
+}
+!1 = !{!1, !2}
+!2 = !{!"llvm.licm.disable"}
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