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[LoopSimplify] Preserve LCSSA when merging exit blocks. 

Summary:
This fixes PR26682. Also add LCSSA as a preserved pass to LoopSimplify,
that looks correct to me and allows to write a test for the issue.

Reviewers: chandlerc, bogner, sanjoy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D21112

llvm-svn: 272224
This commit is contained in:
Michael Zolotukhin 2016-06-08 23:13:21 +00:00
parent 170988f21f
commit 8e7e76729d
2 changed files with 53 additions and 2 deletions
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23
llvm/lib/Transforms/Utils/LoopSimplify.cpp
View File

@ -686,8 +686,10 @@ ReprocessLoop:
}
DT->eraseNode(ExitingBlock);
BI->getSuccessor(0)->removePredecessor(ExitingBlock);
BI->getSuccessor(1)->removePredecessor(ExitingBlock);
BI->getSuccessor(0)->removePredecessor(
ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
BI->getSuccessor(1)->removePredecessor(
ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
ExitingBlock->eraseFromParent();
}
}
@ -748,6 +750,7 @@ namespace {
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<ScalarEvolutionWrapperPass>();
AU.addPreserved<SCEVAAWrapperPass>();
AU.addPreservedID(LCSSAID);
AU.addPreserved<DependenceAnalysisWrapperPass>();
AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
}
@ -781,11 +784,27 @@ bool LoopSimplify::runOnFunction(Function &F) {
SE = SEWP ? &SEWP->getSE() : nullptr;
AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
#ifndef NDEBUG
if (PreserveLCSSA) {
assert(DT && "DT not available.");
assert(LI && "LI not available.");
bool InLCSSA =
all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
assert(InLCSSA && "Requested to preserve LCSSA, but it's already broken.");
}
#endif
// Simplify each loop nest in the function.
for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
Changed |= simplifyLoop(*I, DT, LI, SE, AC, PreserveLCSSA);
#ifndef NDEBUG
if (PreserveLCSSA) {
bool InLCSSA =
all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
assert(InLCSSA && "LCSSA is broken after loop-simplify.");
}
#endif
return Changed;
}

32
llvm/test/Transforms/LoopSimplify/pr26682.ll Normal file
View File

@ -0,0 +1,32 @@
; RUN: opt < %s -lcssa -loop-simplify -indvars -S | FileCheck %s
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-unknown"
@a = external global i32, align 4
; Check that loop-simplify merges two loop exits, but preserves LCSSA form.
; CHECK-LABEL: @foo
; CHECK: for:
; CHECK: %or.cond = and i1 %cmp1, %cmp2
; CHECK-NOT: for.cond:
; CHECK: for.end:
; CHECK: %a.lcssa = phi i32 [ %a, %for ]
define i32 @foo(i32 %x) {
entry:
br label %for
for:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %for.cond ]
%cmp1 = icmp eq i32 %x, 0
%iv.next = add nuw nsw i32 %iv, 1
%a = load i32, i32* @a
br i1 %cmp1, label %for.cond, label %for.end
for.cond:
%cmp2 = icmp slt i32 %iv.next, 4
br i1 %cmp2, label %for, label %for.end
for.end:
%a.lcssa = phi i32 [ %a, %for ], [ %a, %for.cond ]
ret i32 %a.lcssa
}