[llvm] r235232 - [MemCpyOpt] Optimize double-storing by memset+memcpy.
Ahmed Bougacha
ahmed.bougacha at gmail.com
Fri Apr 17 15:20:57 PDT 2015
Author: ab
Date: Fri Apr 17 17:20:57 2015
New Revision: 235232
URL: http://llvm.org/viewvc/llvm-project?rev=235232&view=rev
Log:
[MemCpyOpt] Optimize double-storing by memset+memcpy.
A common idiom in some code is to do the following:
memset(dst, 0, dst_size);
memcpy(dst, src, src_size);
Some of the memset is redundant; instead, we can do:
memcpy(dst, src, src_size);
memset(dst + src_size, 0,
dst_size <= src_size ? 0 : dst_size - src_size);
Original patch by: Joel Jones
Differential Revision: http://reviews.llvm.org/D498
Added:
llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp?rev=235232&r1=235231&r2=235232&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp Fri Apr 17 17:20:57 2015
@@ -346,6 +346,7 @@ namespace {
uint64_t cpyLen, unsigned cpyAlign, CallInst *C);
bool processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
uint64_t MSize);
+ bool processMemSetMemCpyDependence(MemCpyInst *M, MemSetInst *MDep);
bool processByValArgument(CallSite CS, unsigned ArgNo);
Instruction *tryMergingIntoMemset(Instruction *I, Value *StartPtr,
Value *ByteVal);
@@ -839,6 +840,53 @@ bool MemCpyOpt::processMemCpyMemCpyDepen
return true;
}
+/// We've found that the (upward scanning) memory dependence of \p MemCpy is
+/// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that
+/// weren't copied over by \p MemCpy.
+///
+/// In other words, transform:
+/// \code
+/// memset(dst, c, dst_size);
+/// memcpy(dst, src, src_size);
+/// \endcode
+/// into:
+/// \code
+/// memcpy(dst, src, src_size);
+/// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size);
+/// \endcode
+bool MemCpyOpt::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
+ MemSetInst *MemSet) {
+ // We can only transform memset/memcpy with the same destination.
+ if (MemSet->getDest() != MemCpy->getDest())
+ return false;
+
+ Value *Dest = MemSet->getDest();
+ Value *DestSize = MemSet->getLength();
+ Value *SrcSize = MemCpy->getLength();
+
+ // By default, create an unaligned memset.
+ unsigned Align = 1;
+ // If Dest is aligned, and SrcSize is constant, use the minimum alignment
+ // of the sum.
+ const unsigned DestAlign =
+ std::max(MemSet->getAlignment(), MemCpy->getAlignment());
+ if (DestAlign > 1)
+ if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
+ Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
+
+ IRBuilder<> Builder(MemCpy->getNextNode());
+
+ Value *MemsetLen =
+ Builder.CreateSelect(Builder.CreateICmpULE(DestSize, SrcSize),
+ ConstantInt::getNullValue(DestSize->getType()),
+ Builder.CreateSub(DestSize, SrcSize));
+ Builder.CreateMemSet(Builder.CreateGEP(Dest, SrcSize), MemSet->getOperand(1),
+ MemsetLen, Align);
+
+ MD->removeInstruction(MemSet);
+ MemSet->eraseFromParent();
+ return true;
+}
/// processMemCpy - perform simplification of memcpy's. If we have memcpy A
/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
@@ -869,6 +917,17 @@ bool MemCpyOpt::processMemCpy(MemCpyInst
return true;
}
+ AliasAnalysis::Location SrcLoc = AliasAnalysis::getLocationForSource(M);
+ MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(SrcLoc, true,
+ M, M->getParent());
+
+ // Try to turn a partially redundant memset + memcpy into
+ // memcpy + smaller memset. We don't need the memcpy size for this.
+ if (SrcDepInfo.isClobber())
+ if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst()))
+ if (processMemSetMemCpyDependence(M, MDep))
+ return true;
+
// The optimizations after this point require the memcpy size.
ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
if (!CopySize) return false;
@@ -892,9 +951,6 @@ bool MemCpyOpt::processMemCpy(MemCpyInst
}
}
- AliasAnalysis::Location SrcLoc = AliasAnalysis::getLocationForSource(M);
- MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(SrcLoc, true,
- M, M->getParent());
if (SrcDepInfo.isClobber()) {
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue());
Added: llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll?rev=235232&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll (added)
+++ llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll Fri Apr 17 17:20:57 2015
@@ -0,0 +1,54 @@
+; RUN: opt -memcpyopt -S %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; CHECK-LABEL: define void @test
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %src_size, i32 1, i1 false)
+; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i64 %src_size
+; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i64 %dst_size, %src_size
+; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i64 %dst_size, %src_size
+; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i64 0, i64 [[SIZEDIFF]]
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[DST]], i8 0, i64 [[SIZE]], i32 1, i1 false)
+; CHECK-NEXT: ret void
+define void @test(i8* %src, i64 %src_size, i8* %dst, i64 %dst_size) {
+ call void @llvm.memset.p0i8.i64(i8* %dst, i8 0, i64 %dst_size, i32 1, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %src_size, i32 1, i1 false)
+ ret void
+}
+
+; CHECK-LABEL: define void @test_align_same
+; CHECK: call void @llvm.memset.p0i8.i64(i8* {{.*}}, i8 0, i64 {{.*}}, i32 8, i1 false)
+define void @test_align_same(i8* %src, i8* %dst, i64 %dst_size) {
+ call void @llvm.memset.p0i8.i64(i8* %dst, i8 0, i64 %dst_size, i32 8, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 80, i32 1, i1 false)
+ ret void
+}
+
+; CHECK-LABEL: define void @test_align_min
+; CHECK: call void @llvm.memset.p0i8.i64(i8* {{.*}}, i8 0, i64 {{.*}}, i32 4, i1 false)
+define void @test_align_min(i8* %src, i8* %dst, i64 %dst_size) {
+ call void @llvm.memset.p0i8.i64(i8* %dst, i8 0, i64 %dst_size, i32 8, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 36, i32 1, i1 false)
+ ret void
+}
+
+; CHECK-LABEL: define void @test_align_memcpy
+; CHECK: call void @llvm.memset.p0i8.i64(i8* {{.*}}, i8 0, i64 {{.*}}, i32 8, i1 false)
+define void @test_align_memcpy(i8* %src, i8* %dst, i64 %dst_size) {
+ call void @llvm.memset.p0i8.i64(i8* %dst, i8 0, i64 %dst_size, i32 1, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 80, i32 8, i1 false)
+ ret void
+}
+
+; CHECK-LABEL: define void @test_different_dst
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %dst, i8 0, i64 %dst_size, i32 1, i1 false)
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst2, i8* %src, i64 %src_size, i32 1, i1 false)
+; CHECK-NEXT: ret void
+define void @test_different_dst(i8* %dst2, i8* %src, i64 %src_size, i8* %dst, i64 %dst_size) {
+ call void @llvm.memset.p0i8.i64(i8* %dst, i8 0, i64 %dst_size, i32 1, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst2, i8* %src, i64 %src_size, 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)
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