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A memcpy out of an fresh alloca is a no-op, delete it. Patch by Patrick Walton!

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llvm-svn: 200907
This commit is contained in:
Nick Lewycky 2014-02-06 06:29:19 +00:00
parent 53fbc4f3ca
commit 03b9ed1b7b
2 changed files with 36 additions and 1 deletions
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12
lib/Transforms/Scalar/MemCpyOptimizer.cpp
View File

@ -843,9 +843,12 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
if (CopySize == 0) return false;
// The are two possible optimizations we can do for memcpy:
// The are three possible optimizations we can do for memcpy:
// a) memcpy-memcpy xform which exposes redundance for DSE.
// b) call-memcpy xform for return slot optimization.
// c) memcpy from freshly alloca'd space copies undefined data, and we can
// therefore eliminate the memcpy in favor of the data that was already
// at the destination.
MemDepResult DepInfo = MD->getDependency(M);
if (DepInfo.isClobber()) {
if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
@ -865,6 +868,13 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
if (SrcDepInfo.isClobber()) {
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue());
} else if (SrcDepInfo.isDef()) {
if (isa<AllocaInst>(SrcDepInfo.getInst())) {
MD->removeInstruction(M);
M->eraseFromParent();
++NumMemCpyInstr;
return true;
}
}
return false;

25
test/Transforms/MemCpyOpt/memcpy-undef.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: opt < %s -basicaa -memcpyopt -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.8.0"
%struct.foo = type { i8, [7 x i8], i32 }
define i32 @test1(%struct.foo* nocapture %foobie) nounwind noinline ssp uwtable {
%bletch.sroa.1 = alloca [7 x i8], align 1
%1 = getelementptr inbounds %struct.foo* %foobie, i64 0, i32 0
store i8 98, i8* %1, align 4
%2 = getelementptr inbounds %struct.foo* %foobie, i64 0, i32 1, i64 0
%3 = getelementptr inbounds [7 x i8]* %bletch.sroa.1, i64 0, i64 0
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* %3, i64 7, i32 1, i1 false)
%4 = getelementptr inbounds %struct.foo* %foobie, i64 0, i32 2
store i32 20, i32* %4, align 4
ret i32 undef
; Check that the memcpy is removed.
; CHECK-LABEL: @test1(
; CHECK-NOT: call void @llvm.memcpy
}
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind