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1. "Upgrage" comments. 

2. Using zero-extended value of Scale and unsigned division is safe provided
   that Scale doesn't have the sign bit set.
   Previously these 2 instructions:
        %p = bitcast [100 x {i8,i8,i8}]* %x to i8*
        %q = getelementptr i8* %p, i32 -4
   were combined into:
        %q = getelementptr [100 x { i8, i8, i8 }]* %x, i32 0,
               i32 1431655764, i32 0
   what was incorrect.

llvm-svn: 44936
This commit is contained in:
Wojciech Matyjewicz 2007-12-12 15:21:32 +00:00
parent 17c405d29e
commit 309e5a723b
2 changed files with 26 additions and 15 deletions
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31
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -8879,8 +8879,8 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
if (!isa<PointerType>(X->getType())) {
// Not interesting. Source pointer must be a cast from pointer.
} else if (HasZeroPointerIndex) {
// transform: GEP (cast [10 x ubyte]* X to [0 x ubyte]*), long 0, ...
// into : GEP [10 x ubyte]* X, long 0, ...
// transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
// into : GEP [10 x i8]* X, i32 0, ...
//
// This occurs when the program declares an array extern like "int X[];"
//
@ -8900,8 +8900,8 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
}
} else if (GEP.getNumOperands() == 2) {
// Transform things like:
// %t = getelementptr ubyte* cast ([2 x int]* %str to uint*), uint %V
// into: %t1 = getelementptr [2 x int*]* %str, int 0, uint %V; cast
// %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V
// into: %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast
const Type *SrcElTy = cast<PointerType>(X->getType())->getElementType();
const Type *ResElTy=cast<PointerType>(PtrOp->getType())->getElementType();
if (isa<ArrayType>(SrcElTy) &&
@ -8917,12 +8917,11 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
}
// Transform things like:
// getelementptr sbyte* cast ([100 x double]* X to sbyte*), int %tmp
// getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
// (where tmp = 8*tmp2) into:
// getelementptr [100 x double]* %arr, int 0, int %tmp.2
// getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
if (isa<ArrayType>(SrcElTy) &&
(ResElTy == Type::Int8Ty || ResElTy == Type::Int8Ty)) {
if (isa<ArrayType>(SrcElTy) && ResElTy == Type::Int8Ty) {
uint64_t ArrayEltSize =
TD->getABITypeSize(cast<ArrayType>(SrcElTy)->getElementType());
@ -8949,16 +8948,18 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
NewIdx = Inst->getOperand(0);
}
}
// If the index will be to exactly the right offset with the scale taken
// out, perform the transformation.
if (Scale && Scale->getZExtValue() % ArrayEltSize == 0) {
if (isa<ConstantInt>(Scale))
Scale = ConstantInt::get(Scale->getType(),
Scale->getZExtValue() / ArrayEltSize);
// out, perform the transformation. Note, we don't know whether Scale is
// signed or not. We'll use unsigned version of division/modulo
// operation after making sure Scale doesn't have the sign bit set.
if (Scale && Scale->getSExtValue() >= 0LL &&
Scale->getZExtValue() % ArrayEltSize == 0) {
Scale = ConstantInt::get(Scale->getType(),
Scale->getZExtValue() / ArrayEltSize);
if (Scale->getZExtValue() != 1) {
Constant *C = ConstantExpr::getIntegerCast(Scale, NewIdx->getType(),
true /*SExt*/);
false /*ZExt*/);
Instruction *Sc = BinaryOperator::createMul(NewIdx, C, "idxscale");
NewIdx = InsertNewInstBefore(Sc, GEP);
}

10
llvm/test/Transforms/InstCombine/2007-12-12-GEPScale.ll Normal file
View File

@ -0,0 +1,10 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep 1431655764
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-f80:32:32"
define i8* @foo([100 x {i8,i8,i8}]* %x) {
entry:
%p = bitcast [100 x {i8,i8,i8}]* %x to i8*
%q = getelementptr i8* %p, i32 -4
ret i8* %q
}