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[InstCombine] Avoid combining the bitcast of a var that is used as both address and result of load instructions

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This patch fixes https://llvm.org/bugs/show_bug.cgi?id=27703.

If there is a sequence of one or more load instructions, each loaded value is used as address of later load instruction, bitcast is necessary to change the value type, don't optimize it.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270135 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Guozhi Wei 2016-05-19 21:07:01 +00:00
parent 890e6002dc
commit 4f4b87e938
2 changed files with 27 additions and 0 deletions
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7
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -1820,6 +1820,13 @@ Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
auto *LI = dyn_cast<LoadInst>(IncValue);
if (LI) {
// If there is a sequence of one or more load instructions, each loaded
// value is used as address of later load instruction, bitcast is
// necessary to change the value type, don't optimize it. For
// simplicity we give up if the load address comes from another load.
Value *Addr = LI->getOperand(0);
if (Addr == &CI || isa<LoadInst>(Addr))
return nullptr;
if (LI->hasOneUse() && LI->isSimple())
continue;
// If a LoadInst has more than one use, changing the type of loaded

20
test/Transforms/InstCombine/pr27703.ll Normal file
View File

@ -0,0 +1,20 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
define void @mem() {
bb:
br label %bb6
bb6:
%.0 = phi i8** [ undef, %bb ], [ %t2, %bb6 ]
%tmp = load i8*, i8** %.0, align 8
%bc = bitcast i8* %tmp to i8**
%t1 = load i8*, i8** %bc, align 8
%t2 = bitcast i8* %t1 to i8**
br label %bb6
bb206:
ret void
; CHECK: phi
; CHECK: bitcast
; CHECK: load
}