Author: wmat
Date: Wed Dec 12 09:21:32 2007
New Revision: 44936
URL: http://llvm.org/viewvc/llvm-project?rev=44936&view=rev
Log:
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.
Added:
llvm/trunk/test/Transforms/InstCombine/2007-12-12-GEPScale.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=44936&r1=44935&r2=44936&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Wed Dec 12
09:21:32 2007
@@ -8879,8 +8879,8 @@
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 @@
}
} 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 @@
}
// 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 @@
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);
}
Added: llvm/trunk/test/Transforms/InstCombine/2007-12-12-GEPScale.ll
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2007-12-12-GEPScale.ll?rev=44936&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2007-12-12-GEPScale.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2007-12-12-GEPScale.ll Wed Dec 12
09:21:32 2007
@@ -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
+}
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