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Fix a bug in the over-index constant folding. When over-indexing an
array member of a struct, it's possible to land in an arbitrary position inside that struct, such that attempting to find further getelementptr indices will fail. In such cases, folding cannot be done. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79485 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -165,8 +165,11 @@ static Constant *SymbolicallyEvaluateGEP(Constant* const* Ops, unsigned NumOps,
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// Also, this helps GlobalOpt do SROA on GlobalVariables.
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const Type *Ty = Ptr->getType();
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SmallVector<Constant*, 32> NewIdxs;
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for (unsigned Index = 1; Index != NumOps; ++Index) {
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do {
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if (const SequentialType *ATy = dyn_cast<SequentialType>(Ty)) {
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// The only pointer indexing we'll do is on the first index of the GEP.
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if (isa<PointerType>(ATy) && ATy != Ptr->getType())
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break;
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// Determine which element of the array the offset points into.
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uint64_t ElemSize = TD->getTypeAllocSize(ATy->getElementType());
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if (ElemSize == 0)
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@ -183,20 +186,33 @@ static Constant *SymbolicallyEvaluateGEP(Constant* const* Ops, unsigned NumOps,
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Offset -= SL.getElementOffset(ElIdx);
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Ty = STy->getTypeAtIndex(ElIdx);
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} else {
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return 0;
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// We've reached some non-indexable type.
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break;
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}
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}
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} while (Ty != cast<PointerType>(ResultTy)->getElementType());
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// If we haven't used up the entire offset by descending the static
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// type, then the offset is pointing into the middle of an indivisible
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// member, so we can't simplify it.
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if (Offset != 0)
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return 0;
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// If the base is the start of a GlobalVariable and all the array indices
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// remain in their static bounds, the GEP is inbounds. We can check that
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// all indices are in bounds by just checking the first index only
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// because we've just normalized all the indices.
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if (isa<GlobalVariable>(Ptr) && NewIdxs[0]->isNullValue())
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return ConstantExpr::getInBoundsGetElementPtr(Ptr,
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&NewIdxs[0], NewIdxs.size());
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Constant *C = isa<GlobalVariable>(Ptr) && NewIdxs[0]->isNullValue() ?
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ConstantExpr::getInBoundsGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size()) :
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ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size());
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assert(cast<PointerType>(C->getType())->getElementType() == Ty &&
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"Computed GetElementPtr has unexpected type!");
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// Otherwise it may not be inbounds.
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return ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size());
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// If we ended up indexing a member with a type that doesn't match
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// type type of what the original indices indexed, add a cast.
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if (Ty != cast<PointerType>(ResultTy)->getElementType())
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C = ConstantExpr::getBitCast(C, ResultTy);
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return C;
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}
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/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with
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17
test/Transforms/InstCombine/constant-fold-gep-overindex.ll
Normal file
17
test/Transforms/InstCombine/constant-fold-gep-overindex.ll
Normal file
@ -0,0 +1,17 @@
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; RUN: llvm-as < %s | opt -instcombine
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target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
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target triple = "i386-apple-darwin10.0"
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%0 = type { i8*, [19 x i8] }
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%1 = type { i8*, [0 x i8] }
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@s = external global %0 ; <%0*> [#uses=1]
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@"\01LC8" = external constant [17 x i8] ; <[17 x i8]*> [#uses=1]
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define i32 @main() nounwind {
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entry:
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%0 = call i32 (i8*, ...)* @printf(i8* getelementptr ([17 x i8]* @"\01LC8", i32 0, i32 0), i8* undef, i8* getelementptr (%1* bitcast (%0* @s to %1*), i32 0, i32 1, i32 0)) nounwind ; <i32> [#uses=0]
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ret i32 0
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}
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declare i32 @printf(i8*, ...) nounwind
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