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Fix PR2355: bug in ChangeCompareStride. When the loop termination compare is the only use of its iv stride, the stride can be eliminated by moving it to another stride. If the scale is negative, swap the predicate instead of using a inverse predicate. 

llvm-svn: 54415
This commit is contained in:
Evan Cheng 2008-08-06 18:04:43 +00:00
parent 2dd3e4e49d
commit 907dc2bc37
2 changed files with 26 additions and 2 deletions
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4
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -1624,10 +1624,10 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
continue;
}
// If scale is negative, use inverse predicate unless it's testing
// If scale is negative, use swapped predicate unless it's testing
// for equality.
if (Scale < 0 && !Cond->isEquality())
Predicate = ICmpInst::getInversePredicate(Predicate);
Predicate = ICmpInst::getSwappedPredicate(Predicate);
NewStride = &StrideOrder[i];
break;

24
llvm/test/Transforms/LoopStrengthReduce/2008-08-06-CmpStride.ll Normal file
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@ -0,0 +1,24 @@
; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep ugt
; PR2355
@.str = internal constant [4 x i8] c"%d\0A\00"
declare i32 @printf(i8* noalias , ...) nounwind
define i32 @main() nounwind {
entry:
br label %forbody
forbody:
%i.0 = phi i32 [ 0, %entry ], [ %inc, %forbody ] ; <i32>[#uses=3]
%sub14 = sub i32 1027, %i.0 ; <i32> [#uses=1]
%mul15 = mul i32 %sub14, 10 ; <i32> [#uses=1]
%add166 = or i32 %mul15, 1 ; <i32> [#uses=1] *
call i32 (i8*, ...)* @printf( i8* noalias getelementptr ([4 x i8]* @.str, i32 0, i32 0), i32 %add166 ) nounwind
%inc = add i32 %i.0, 1 ; <i32> [#uses=3]
%cmp = icmp ult i32 %inc, 1027 ; <i1> [#uses=1]
br i1 %cmp, label %forbody, label %afterfor
afterfor: ; preds = %forcond
ret i32 0
}