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[ShrinkWrap] Fix FindIDom to only have one kind of failure. 

FindIDom() can fail in two different ways - it can either return nullptr or the
block itself, depending on the circumstances. Some users of FindIDom() check
one error condition, while others check the other.

Change it to always return nullptr on failure.
This fixes PR26004.

Differential Revision: http://reviews.llvm.org/D15847

llvm-svn: 256955
This commit is contained in:
Michael Kuperstein 2016-01-06 18:40:11 +00:00
parent b243c95c6a
commit 037c9984db
2 changed files with 36 additions and 6 deletions
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10
llvm/lib/CodeGen/ShrinkWrap.cpp
View File

@ -263,6 +263,8 @@ MachineBasicBlock *FindIDom(MachineBasicBlock &Block, ListOfBBs BBs,
if (!IDom)
break;
}
if (IDom == &Block)
return nullptr;
return IDom;
}
@ -352,13 +354,9 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
// Push Save outside of this loop if immediate dominator is different
// from save block. If immediate dominator is not different, bail out.
MachineBasicBlock *IDom = FindIDom<>(*Save, Save->predecessors(), *MDT);
if (IDom != Save)
Save = IDom;
else {
Save = nullptr;
Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
if (!Save)
break;
}
} else {
// If the loop does not exit, there is no point in looking
// for a post-dominator outside the loop.

32
llvm/test/CodeGen/X86/shrinkwrap-hang.ll Normal file
View File

@ -0,0 +1,32 @@
; RUN: llc %s -o - -enable-shrink-wrap=true | FileCheck %s
target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
target triple = "i686-pc-linux"
@b = global i32 1, align 4
@a = common global i32 0, align 4
declare void @fn1() #0
; CHECK-LABEL: fn2:
define void @fn2() #0 {
entry:
%0 = load i32, i32* @b, align 4
%tobool = icmp eq i32 %0, 0
br i1 %tobool, label %if.end, label %lbl
lbl: ; preds = %if.end, %entry
store i32 0, i32* @b, align 4
br label %if.end
if.end: ; preds = %entry, %lbl
tail call void @fn1()
%1 = load i32, i32* @b, align 4
%tobool1 = icmp eq i32 %1, 0
br i1 %tobool1, label %if.end3, label %lbl
if.end3: ; preds = %if.end
ret void
}
attributes #0 = { norecurse nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="pentium4" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }