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[LoopUnroll] Don't peel loops where the latch isn't the exiting block 

Peeling assumed this doesn't happen, but didn't check it.
This fixes PR32178.

Differential Revision: https://reviews.llvm.org/D30757

llvm-svn: 297993
This commit is contained in:
Michael Kuperstein 2017-03-16 21:07:48 +00:00
parent 99de88d1f3
commit 2da2bfa088
2 changed files with 43 additions and 0 deletions
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7
llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
View File

@ -56,6 +56,13 @@ static bool canPeel(Loop *L) {
if (!L->getExitingBlock() || !L->getUniqueExitBlock())
return false;
// Don't try to peel loops where the latch is not the exiting block.
// This can be an indication of two different things:
// 1) The loop is not rotated.
// 2) The loop contains irreducible control flow that involves the latch.
if (L->getLoopLatch() != L->getExitingBlock())
return false;
return true;
}

36
llvm/test/Transforms/LoopUnroll/peel-loop-irreducible.ll Normal file
View File

@ -0,0 +1,36 @@
; RUN: opt < %s -S -loop-unroll -unroll-force-peel-count=1 | FileCheck %s
; Check we don't peel loops where the latch is not the exiting block.
; CHECK-LABEL: @invariant_backedge_irreducible
; CHECK: entry:
; CHECK: br label %header
; CHECK-NOT: peel
; CHECK: header:
; CHECK: br i1 {{.*}} label %latch, label %exiting
; CHECK: latch:
; CHECK: br i1 {{.*}} label %header, label %exiting
; CHECK: exiting:
; CHECK: br i1 {{.*}} label %latch, label %exit
define i32 @invariant_backedge_irreducible(i32 %a, i32 %b) {
entry:
br label %header
header:
%i = phi i32 [ 0, %entry ], [ %inc, %latch ]
%cmp.phi = phi i1 [ false, %entry ], [ %cmp, %latch ]
br i1 %cmp.phi, label %latch, label %exiting
latch:
%inc = add i32 %i, 1
%cmp = icmp slt i32 %i, 1000
br i1 %cmp, label %header, label %exiting
exiting:
%cmp.exiting = phi i1 [ %cmp.phi, %header ], [ %cmp, %latch ]
br i1 %cmp.exiting, label %latch, label %exit
exit:
ret i32 0
}