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Add a rather pointless InstructionSimplify transform, inspired by recent constant
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
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@ -18,6 +18,7 @@
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/PatternMatch.h"
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#include "llvm/Support/ValueHandle.h"
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#include "llvm/Target/TargetData.h"
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using namespace llvm;
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using namespace llvm::PatternMatch;
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@ -698,11 +699,18 @@ Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
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//if (isa<UndefValue>(Ops[0]))
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// return UndefValue::get(GEP.getType());
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if (NumOps == 2) {
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// getelementptr P, 0 -> P.
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if (NumOps == 2)
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if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
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if (C->isZero())
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return Ops[0];
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// getelementptr P, N -> P if P points to a type of zero size.
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if (TD) {
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const Type *Ty = cast<PointerType>(Ops[0]->getType())->getElementType();
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if (Ty->isSized() && !TD->getTypeAllocSize(Ty))
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return Ops[0];
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}
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}
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// Check to see if this is constant foldable.
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for (unsigned i = 0; i != NumOps; ++i)
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@ -0,0 +1,8 @@
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; RUN: opt < %s -instcombine -S | not grep getelementptr
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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"
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define {}* @foo({}* %x, i32 %n) {
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%p = getelementptr {}* %x, i32 %n
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ret {}* %p
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}
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