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Suppress the IV reversal transformation in the case that the RHS
of the comparison is defined inside the loop. This fixes a use-before-def problem, because the transformation puts a use of the RHS outside the loop. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72149 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2456,6 +2456,11 @@ void LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
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SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
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if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One)
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return;
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// If the RHS of the comparison is defined inside the loop, the rewrite
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// cannot be done.
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if (Instruction *CR = dyn_cast<Instruction>(Cond->getOperand(1)))
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if (L->contains(CR->getParent()))
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return;
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// Make sure the IV is only used for counting. Value may be preinc or
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// postinc; 2 uses in either case.
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21
test/Transforms/LoopStrengthReduce/dont_reverse.ll
Normal file
21
test/Transforms/LoopStrengthReduce/dont_reverse.ll
Normal file
@ -0,0 +1,21 @@
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; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis \
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; RUN: | grep {icmp eq i2 %lsr.iv.next, %xmp4344}
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; Don't reverse the iteration if the rhs of the compare is defined
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; inside the loop.
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define void @Fill_Buffer() nounwind {
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entry:
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br label %bb8
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bb8:
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%indvar34 = phi i32 [ 0, %entry ], [ %indvar.next35, %bb8 ]
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%indvar3451 = trunc i32 %indvar34 to i2
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%xmp4344 = xor i2 0, -1
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%xmp104 = icmp eq i2 %indvar3451, %xmp4344
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%indvar.next35 = add i32 %indvar34, 1
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br i1 %xmp104, label %bb10, label %bb8
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bb10:
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unreachable
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}
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