[llvm] r272224 - [LoopSimplify] Preserve LCSSA when merging exit blocks.

[Michael Zolotukhin via llvm-commits]

Hi Mikael,

Thanks for reporting, I’ll take a look!

Michael

> On Jun 22, 2016, at 1:25 AM, Mikael Holmén <mikael.holmen at ericsson.com> wrote:
> 
> Hi Michael,
> 
> The checks introduced in this commit fail on:
> 
> opt -S -lcssa -loop-unroll red.ll
> 
> I don't know if it's the checks or the optimization that is actually wrong.
> 
> Regards,
> Mikael
> 
> On 06/09/2016 01:13 AM, Michael Zolotukhin via llvm-commits wrote:
>> Author: mzolotukhin
>> Date: Wed Jun  8 18:13:21 2016
>> New Revision: 272224
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=272224&view=rev
>> Log:
>> [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
>> 
>> Added:
>>     llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll
>> Modified:
>>     llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
>> 
>> Modified: llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp?rev=272224&r1=272223&r2=272224&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp Wed Jun  8 18:13:21 2016
>> @@ -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(Functio
>>    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;
>>  }
>> 
>> 
>> Added: llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll?rev=272224&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll (added)
>> +++ llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll Wed Jun  8 18:13:21 2016
>> @@ -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"
>> +
>> + at 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
>> +}
>> 
>> 
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