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Make LoopDeletion check the maximum backedge taken count, rather than the

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exact backedge taken count, when checking for infinite loops. This allows
it to delete loops with multiple exit conditions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84952 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-10-23 17:10:01 +00:00
parent 9ff9b34dd1
commit 934af9cfe0
2 changed files with 28 additions and 1 deletions
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2
lib/Transforms/Scalar/LoopDeletion.cpp
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@ -167,7 +167,7 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) {
// Don't remove loops for which we can't solve the trip count.
// They could be infinite, in which case we'd be changing program behavior.
ScalarEvolution& SE = getAnalysis<ScalarEvolution>();
const SCEV *S = SE.getBackedgeTakenCount(L);
const SCEV *S = SE.getMaxBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(S))
return Changed;

27
test/Transforms/LoopDeletion/multiple-exit-conditions.ll Normal file
View File

@ -0,0 +1,27 @@
; RUN: opt < %s -loop-deletion -S | FileCheck %s
; ScalarEvolution can prove the loop iteration is finite, even though
; it can't represent the exact trip count as an expression. That's
; good enough to let the loop be deleted.
; CHECK: entry:
; CHECK-NEXT: br label %return
; CHECK: return:
; CHECK-NEXT: ret void
define void @foo(i64 %n, i64 %m) nounwind {
entry:
br label %bb
bb:
%x.0 = phi i64 [ 0, %entry ], [ %t0, %bb ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
%t3 = icmp sgt i64 %x.0, %m
%t4 = and i1 %t1, %t3
br i1 %t4, label %bb, label %return
return:
ret void
}