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Fix a bug compiling PR1978 (perhaps not the only one though) which 

was incorrectly simplifying "x == (gep x, 1, i)" into false, even 
though i could be negative.  As it turns out, all the code to 
handle this already existed, we just need to disable the incorrect
optimization case and let the general case handle it.

llvm-svn: 46739
This commit is contained in:
Chris Lattner 2008-02-05 04:45:32 +00:00
parent 1de5997119
commit 682a7dc653
2 changed files with 38 additions and 54 deletions
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59
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -4629,60 +4629,11 @@ Instruction *InstCombiner::FoldGEPICmp(User *GEPLHS, Value *RHS,
Value *PtrBase = GEPLHS->getOperand(0);
if (PtrBase == RHS) {
// As an optimization, we don't actually have to compute the actual value of
// OFFSET if this is a icmp_eq or icmp_ne comparison, just return whether
// each index is zero or not.
if (Cond == ICmpInst::ICMP_EQ || Cond == ICmpInst::ICMP_NE) {
Instruction *InVal = 0;
gep_type_iterator GTI = gep_type_begin(GEPLHS);
for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i, ++GTI) {
bool EmitIt = true;
if (Constant *C = dyn_cast<Constant>(GEPLHS->getOperand(i))) {
if (isa<UndefValue>(C)) // undef index -> undef.
return ReplaceInstUsesWith(I, UndefValue::get(I.getType()));
if (C->isNullValue())
EmitIt = false;
else if (TD->getABITypeSize(GTI.getIndexedType()) == 0) {
EmitIt = false; // This is indexing into a zero sized array?
} else if (isa<ConstantInt>(C))
return ReplaceInstUsesWith(I, // No comparison is needed here.
ConstantInt::get(Type::Int1Ty,
Cond == ICmpInst::ICMP_NE));
}
if (EmitIt) {
Instruction *Comp =
new ICmpInst(Cond, GEPLHS->getOperand(i),
Constant::getNullValue(GEPLHS->getOperand(i)->getType()));
if (InVal == 0)
InVal = Comp;
else {
InVal = InsertNewInstBefore(InVal, I);
InsertNewInstBefore(Comp, I);
if (Cond == ICmpInst::ICMP_NE) // True if any are unequal
InVal = BinaryOperator::createOr(InVal, Comp);
else // True if all are equal
InVal = BinaryOperator::createAnd(InVal, Comp);
}
}
}
if (InVal)
return InVal;
else
// No comparison is needed here, all indexes = 0
ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty,
Cond == ICmpInst::ICMP_EQ));
}
// Only lower this if the icmp is the only user of the GEP or if we expect
// the result to fold to a constant!
if (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) {
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
Value *Offset = EmitGEPOffset(GEPLHS, I, *this);
return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset,
Constant::getNullValue(Offset->getType()));
}
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
// This transformation is valid because we know pointers can't overflow.
Value *Offset = EmitGEPOffset(GEPLHS, I, *this);
return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset,
Constant::getNullValue(Offset->getType()));
} else if (User *GEPRHS = dyn_castGetElementPtr(RHS)) {
// If the base pointers are different, but the indices are the same, just
// compare the base pointer.

33
llvm/test/Transforms/InstCombine/2008-02-04-GEPIdxBug.ll Normal file
View File

@ -0,0 +1,33 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {icmp eq i32 %indvar, 0}
; PR1978
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"
target triple = "i686-apple-darwin8"
%struct.x = type <{ i8 }>
@.str = internal constant [6 x i8] c"Main!\00" ; <[6 x i8]*> [#uses=1]
@.str1 = internal constant [12 x i8] c"destroy %p\0A\00" ; <[12 x i8]*> [#uses=1]
define i32 @main() nounwind {
entry:
%orientations = alloca [1 x [1 x %struct.x]] ; <[1 x [1 x %struct.x]]*> [#uses=2]
%tmp3 = call i32 @puts( i8* getelementptr ([6 x i8]* @.str, i32 0, i32 0) ) nounwind ; <i32> [#uses=0]
%tmp45 = getelementptr [1 x [1 x %struct.x]]* %orientations, i32 1, i32 0, i32 0 ; <%struct.x*> [#uses=1]
%orientations62 = getelementptr [1 x [1 x %struct.x]]* %orientations, i32 0, i32 0, i32 0 ; <%struct.x*> [#uses=1]
br label %bb10
bb10: ; preds = %bb10, %entry
%indvar = phi i32 [ 0, %entry ], [ %indvar.next, %bb10 ] ; <i32> [#uses=2]
%tmp.0.reg2mem.0.rec = mul i32 %indvar, -1 ; <i32> [#uses=1]
%tmp12.rec = add i32 %tmp.0.reg2mem.0.rec, -1 ; <i32> [#uses=1]
%tmp12 = getelementptr %struct.x* %tmp45, i32 %tmp12.rec ; <%struct.x*> [#uses=2]
%tmp16 = call i32 (i8*, ...)* @printf( i8* getelementptr ([12 x i8]* @.str1, i32 0, i32 0), %struct.x* %tmp12 ) nounwind ; <i32> [#uses=0]
%tmp84 = icmp eq %struct.x* %tmp12, %orientations62 ; <i1> [#uses=1]
%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=1]
br i1 %tmp84, label %bb17, label %bb10
bb17: ; preds = %bb10
ret i32 0
}
declare i32 @puts(i8*)
declare i32 @printf(i8*, ...)