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Add a rather pointless InstructionSimplify transform, inspired by recent constant

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folding improvements: if P points to a type of size zero, turn "gep P, N" into "P".
More generally, if a gep index type has size zero, instcombine could replace the
index with zero, but that is not done here.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119942 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2010-11-21 13:53:09 +00:00
parent e58391073f
commit e60d79faf7
2 changed files with 18 additions and 2 deletions
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12
lib/Analysis/InstructionSimplify.cpp
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@ -18,6 +18,7 @@
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
using namespace llvm::PatternMatch;
@ -698,11 +699,18 @@ Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
//if (isa<UndefValue>(Ops[0]))
// return UndefValue::get(GEP.getType());
// getelementptr P, 0 -> P.
if (NumOps == 2)
if (NumOps == 2) {
// getelementptr P, 0 -> P.
if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
if (C->isZero())
return Ops[0];
// getelementptr P, N -> P if P points to a type of zero size.
if (TD) {
const Type *Ty = cast<PointerType>(Ops[0]->getType())->getElementType();
if (Ty->isSized() && !TD->getTypeAllocSize(Ty))
return Ops[0];
}
}
// Check to see if this is constant foldable.
for (unsigned i = 0; i != NumOps; ++i)

8
test/Transforms/InstCombine/2010-11-21-SizeZeroTypeGEP.ll Normal file
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@ -0,0 +1,8 @@
; RUN: opt < %s -instcombine -S | not grep getelementptr
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"
define {}* @foo({}* %x, i32 %n) {
%p = getelementptr {}* %x, i32 %n
ret {}* %p
}