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GlobalOpt: If we have an inbounds GEP from a ConstantAggregateZero global that we just determined to be constant, replace all loads from it with a zero value.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153576 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-03-28 14:50:09 +00:00
parent 9b58464330
commit c1ea16ec43
2 changed files with 17 additions and 0 deletions
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6
lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -341,6 +341,12 @@ static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
// If the initializer is an all-null value and we have an inbounds GEP,
// we already know what the result of any load from that GEP is.
// TODO: Handle splats.
if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
SubInit = Constant::getNullValue(GEP->getType()->getElementType());
}
Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);

11
test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll Normal file
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@ -0,0 +1,11 @@
; RUN: opt < %s -S -globalopt | FileCheck %s
@zero = internal global [10 x i32] zeroinitializer
define i32 @test1(i64 %idx) nounwind {
%arrayidx = getelementptr inbounds [10 x i32]* @zero, i64 0, i64 %idx
%l = load i32* %arrayidx
ret i32 %l
; CHECK: @test1
; CHECK: ret i32 0
}