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Suppress the IV reversal transformation in the case that the RHS

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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
This commit is contained in:
Dan Gohman 2009-05-20 00:34:08 +00:00
parent 81e4e9f7cb
commit 513fae2db5
2 changed files with 26 additions and 0 deletions
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5
lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -2456,6 +2456,11 @@ void LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType()); SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One) if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One)
return; return;
// If the RHS of the comparison is defined inside the loop, the rewrite
// cannot be done.
if (Instruction *CR = dyn_cast<Instruction>(Cond->getOperand(1)))
if (L->contains(CR->getParent()))
return;
// Make sure the IV is only used for counting. Value may be preinc or // Make sure the IV is only used for counting. Value may be preinc or
// postinc; 2 uses in either case. // postinc; 2 uses in either case.

21
test/Transforms/LoopStrengthReduce/dont_reverse.ll Normal file
View File

@ -0,0 +1,21 @@
; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis \
; RUN: | grep {icmp eq i2 %lsr.iv.next, %xmp4344}
; Don't reverse the iteration if the rhs of the compare is defined
; inside the loop.
define void @Fill_Buffer() nounwind {
entry:
br label %bb8
bb8:
%indvar34 = phi i32 [ 0, %entry ], [ %indvar.next35, %bb8 ]
%indvar3451 = trunc i32 %indvar34 to i2
%xmp4344 = xor i2 0, -1
%xmp104 = icmp eq i2 %indvar3451, %xmp4344
%indvar.next35 = add i32 %indvar34, 1
br i1 %xmp104, label %bb10, label %bb8
bb10:
unreachable
}