[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
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@ -686,8 +686,10 @@ ReprocessLoop:
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}
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DT->eraseNode(ExitingBlock);
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BI->getSuccessor(0)->removePredecessor(ExitingBlock);
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BI->getSuccessor(1)->removePredecessor(ExitingBlock);
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BI->getSuccessor(0)->removePredecessor(
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ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
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BI->getSuccessor(1)->removePredecessor(
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ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
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ExitingBlock->eraseFromParent();
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}
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}
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@ -748,6 +750,7 @@ namespace {
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AU.addPreserved<GlobalsAAWrapperPass>();
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AU.addPreserved<ScalarEvolutionWrapperPass>();
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AU.addPreserved<SCEVAAWrapperPass>();
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AU.addPreservedID(LCSSAID);
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AU.addPreserved<DependenceAnalysisWrapperPass>();
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AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
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}
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@ -781,11 +784,27 @@ bool LoopSimplify::runOnFunction(Function &F) {
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SE = SEWP ? &SEWP->getSE() : nullptr;
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AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
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bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
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#ifndef NDEBUG
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if (PreserveLCSSA) {
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assert(DT && "DT not available.");
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assert(LI && "LI not available.");
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bool InLCSSA =
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all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
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assert(InLCSSA && "Requested to preserve LCSSA, but it's already broken.");
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}
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#endif
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// Simplify each loop nest in the function.
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for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
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Changed |= simplifyLoop(*I, DT, LI, SE, AC, PreserveLCSSA);
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#ifndef NDEBUG
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if (PreserveLCSSA) {
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bool InLCSSA =
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all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
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assert(InLCSSA && "LCSSA is broken after loop-simplify.");
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}
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#endif
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return Changed;
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}
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@ -0,0 +1,32 @@
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; RUN: opt < %s -lcssa -loop-simplify -indvars -S | FileCheck %s
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target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-unknown"
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@a = external global i32, align 4
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; Check that loop-simplify merges two loop exits, but preserves LCSSA form.
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; CHECK-LABEL: @foo
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; CHECK: for:
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; CHECK: %or.cond = and i1 %cmp1, %cmp2
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; CHECK-NOT: for.cond:
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; CHECK: for.end:
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; CHECK: %a.lcssa = phi i32 [ %a, %for ]
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define i32 @foo(i32 %x) {
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entry:
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br label %for
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for:
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%iv = phi i32 [ 0, %entry ], [ %iv.next, %for.cond ]
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%cmp1 = icmp eq i32 %x, 0
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%iv.next = add nuw nsw i32 %iv, 1
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%a = load i32, i32* @a
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br i1 %cmp1, label %for.cond, label %for.end
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for.cond:
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%cmp2 = icmp slt i32 %iv.next, 4
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br i1 %cmp2, label %for, label %for.end
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for.end:
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%a.lcssa = phi i32 [ %a, %for ], [ %a, %for.cond ]
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ret i32 %a.lcssa
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}
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