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[MemCpyOpt] Do move the memset, but look at its dest's dependencies.

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In effect a partial revert of r237858, which was a dumb shortcut.
Looking at the dependencies of the destination should be the proper
fix: if the new memset would depend on anything other than itself,
the transformation isn't correct.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237874 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ahmed Bougacha 2015-05-21 01:43:39 +00:00
parent 4652459f64
commit 8eca988b00
2 changed files with 29 additions and 2 deletions
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9
lib/Transforms/Scalar/MemCpyOptimizer.cpp
View File

@ -859,6 +859,13 @@ bool MemCpyOpt::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
if (MemSet->getDest() != MemCpy->getDest())
return false;
// Check that there are no other dependencies on the memset destination.
MemDepResult DstDepInfo =
MD->getPointerDependencyFrom(AliasAnalysis::getLocationForDest(MemSet),
false, MemCpy, MemCpy->getParent());
if (DstDepInfo.getInst() != MemSet)
return false;
// Use the same i8* dest as the memcpy, killing the memset dest if different.
Value *Dest = MemCpy->getRawDest();
Value *DestSize = MemSet->getLength();
@ -874,7 +881,7 @@ bool MemCpyOpt::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
IRBuilder<> Builder(MemSet);
IRBuilder<> Builder(MemCpy);
// If the sizes have different types, zext the smaller one.
if (DestSize->getType() != SrcSize->getType()) {

22
test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
View File

@ -1,4 +1,4 @@
; RUN: opt -memcpyopt -S %s | FileCheck %s
; RUN: opt -basicaa -memcpyopt -S %s | FileCheck %s
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
@ -140,6 +140,26 @@ define i8 @test_intermediate_read(i8* %a, i8* %b) #0 {
ret i8 %r
}
%struct = type { [8 x i8], [8 x i8] }
; CHECK-LABEL: define void @test_intermediate_write
; CHECK-NEXT: %a = alloca %struct
; CHECK-NEXT: %a0 = getelementptr %struct, %struct* %a, i32 0, i32 0, i32 0
; CHECK-NEXT: %a1 = getelementptr %struct, %struct* %a, i32 0, i32 1, i32 0
; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %a0, i8 0, i64 16, i32 1, i1 false)
; CHECK-NEXT: store i8 1, i8* %a1
; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a0, i8* %b, i64 8, i32 1, i1 false)
; CHECK-NEXT: ret void
define void @test_intermediate_write(i8* %b) #0 {
%a = alloca %struct
%a0 = getelementptr %struct, %struct* %a, i32 0, i32 0, i32 0
%a1 = getelementptr %struct, %struct* %a, i32 0, i32 1, i32 0
call void @llvm.memset.p0i8.i64(i8* %a0, i8 0, i64 16, i32 1, i1 false)
store i8 1, i8* %a1
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a0, i8* %b, i64 8, i32 1, i1 false)
ret void
}
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1)
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1)
declare void @llvm.memset.p0i8.i32(i8* nocapture, i8, i32, i32, i1)