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[LoopDeletion] Forget loop before setting values to undef
After D71539, we need to forget the loop before setting the incoming values of phi nodes in exit blocks, because we are looking through those phi nodes now and the SCEV expression could depend on the loop phi. If we update the phi nodes before forgetting the loop, we miss those users during invalidation. Reviewed By: reames Differential Revision: https://reviews.llvm.org/D88167
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‎llvm/lib/Transforms/Scalar/LoopDeletion.cpp

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@@ -165,6 +165,10 @@ static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
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if (ExitBlock && isLoopNeverExecuted(L)) {
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LLVM_DEBUG(dbgs() << "Loop is proven to never execute, delete it!");
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// We need to forget the loop before setting the incoming values of the exit
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// phis to undef, so we properly invalidate the SCEV expressions for those
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// phis.
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SE.forgetLoop(L);
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// Set incoming value to undef for phi nodes in the exit block.
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for (PHINode &P : ExitBlock->phis()) {
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std::fill(P.incoming_values().begin(), P.incoming_values().end(),

‎llvm/lib/Transforms/Utils/LoopUtils.cpp

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@@ -724,6 +724,9 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
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}
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LI->destroy(L);
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}
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if (SE)
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SE->verify();
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}
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/// Checks if \p L has single exit through latch block except possibly

‎llvm/test/Transforms/LoopDeletion/update-scev.ll

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@@ -1,4 +1,4 @@
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; RUN: opt -S -analyze -scalar-evolution -loop-deletion -scalar-evolution < %s | FileCheck %s --check-prefix=SCEV-EXPRS
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; RUN: opt -S -analyze -scalar-evolution -loop-deletion -scalar-evolution -verify-scev < %s | FileCheck %s --check-prefix=SCEV-EXPRS
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; RUN: opt -S -loop-deletion < %s | FileCheck %s --check-prefix=IR-AFTER-TRANSFORM
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; RUN: opt -S -indvars -loop-deletion -indvars < %s | FileCheck %s --check-prefix=ORIGINAL-CRASH
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@@ -54,3 +54,115 @@ for.inc11: ; preds = %for.body6
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for.cond14: ; preds = %for.cond14, %for.inc11
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br i1 undef, label %for.cond, label %for.cond14
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}
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; LoopDeletion removes the loop %for.body7.1. Make sure %inc.lcssa.1 in the loop
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; exit block is correctly invalidated.
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define void @test2(double* %bx, i64 %by) local_unnamed_addr align 2 {
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; IR-AFTER-TRANSFORM-LABEL: @test2(
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; IR-AFTER-TRANSFORM-NOT: for.body7.1:
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; SCEV-EXPRS-LABEL: test2
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; SCEV-EXPRS: %inc.lcssa.1 = phi i64 [ undef, %for.body7.preheader.1 ]
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; SCEV-EXPRS-NEXT: --> undef
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entry:
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%cmp = icmp sgt i64 %by, 0
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br label %for.cond.preheader
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for.cond.preheader: ; preds = %entry
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br i1 %cmp, label %for.cond5.preheader.lr.ph, label %for.end14
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for.cond5.preheader.lr.ph: ; preds = %for.cond.preheader
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br label %for.cond5.preheader
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for.cond.loopexit.loopexit: ; preds = %for.body10
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%inc11.lcssa = phi i64 [ %inc11, %for.body10 ]
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br label %for.cond.loopexit
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for.cond.loopexit: ; preds = %for.cond8.preheader, %for.cond.loopexit.loopexit
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%ca.3.lcssa = phi i64 [ %ca.2.lcssa, %for.cond8.preheader ], [ %inc11.lcssa, %for.cond.loopexit.loopexit ]
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br i1 %cmp, label %for.cond5.preheader, label %for.end14.loopexit
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for.cond5.preheader: ; preds = %for.cond.loopexit, %for.cond5.preheader.lr.ph
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%ca.19 = phi i64 [ 0, %for.cond5.preheader.lr.ph ], [ %ca.3.lcssa, %for.cond.loopexit ]
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br i1 false, label %for.cond8.preheader, label %for.body7.preheader
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for.body7.preheader: ; preds = %for.cond5.preheader
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br label %for.body7
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for.cond8.preheader.loopexit: ; preds = %for.body7
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%inc.lcssa = phi i64 [ %inc, %for.body7 ]
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br label %for.cond8.preheader
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for.cond8.preheader: ; preds = %for.cond8.preheader.loopexit, %for.cond5.preheader
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%ca.2.lcssa = phi i64 [ %ca.19, %for.cond5.preheader ], [ %inc.lcssa, %for.cond8.preheader.loopexit ]
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br i1 true, label %for.body10.preheader, label %for.cond.loopexit
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for.body10.preheader: ; preds = %for.cond8.preheader
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br label %for.body10
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for.body7: ; preds = %for.body7, %for.body7.preheader
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%ca.26 = phi i64 [ %inc, %for.body7 ], [ %ca.19, %for.body7.preheader ]
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%inc = add nsw i64 %ca.26, 1
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%arrayidx = getelementptr inbounds double, double* %bx, i64 %ca.26
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store double 0.000000e+00, double* %arrayidx, align 8
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br i1 false, label %for.cond8.preheader.loopexit, label %for.body7
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for.body10: ; preds = %for.body10, %for.body10.preheader
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%ca.37 = phi i64 [ %inc11, %for.body10 ], [ %ca.2.lcssa, %for.body10.preheader ]
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%inc11 = add nsw i64 %ca.37, 1
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br i1 true, label %for.body10, label %for.cond.loopexit.loopexit
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for.end14.loopexit: ; preds = %for.cond.loopexit
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br label %for.end14
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for.end14: ; preds = %for.end14.loopexit, %for.cond.preheader
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br i1 %cmp, label %for.cond5.preheader.lr.ph.1, label %for.end14.1
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for.cond5.preheader.lr.ph.1: ; preds = %for.end14
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br label %for.cond5.preheader.1
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for.cond5.preheader.1: ; preds = %for.cond.loopexit.1, %for.cond5.preheader.lr.ph.1
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%ca.19.1 = phi i64 [ 0, %for.cond5.preheader.lr.ph.1 ], [ %ca.3.lcssa.1, %for.cond.loopexit.1 ]
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br i1 true, label %for.cond8.preheader.1, label %for.body7.preheader.1
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for.body7.preheader.1: ; preds = %for.cond5.preheader.1
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br label %for.body7.1
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for.body7.1: ; preds = %for.body7.1, %for.body7.preheader.1
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%ca.26.1 = phi i64 [ %inc.1, %for.body7.1 ], [ %ca.19.1, %for.body7.preheader.1 ]
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%inc.1 = add nsw i64 %ca.26.1, 1
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%arrayidx.1 = getelementptr inbounds double, double* %bx, i64 %ca.26.1
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store double 0.000000e+00, double* %arrayidx.1, align 8
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br i1 true, label %for.cond8.preheader.loopexit.1, label %for.body7.1
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for.cond8.preheader.loopexit.1: ; preds = %for.body7.1
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%inc.lcssa.1 = phi i64 [ %inc.1, %for.body7.1 ]
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br label %for.cond8.preheader.1
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for.cond8.preheader.1: ; preds = %for.cond8.preheader.loopexit.1, %for.cond5.preheader.1
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%ca.2.lcssa.1 = phi i64 [ %ca.19.1, %for.cond5.preheader.1 ], [ %inc.lcssa.1, %for.cond8.preheader.loopexit.1 ]
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br i1 false, label %for.body10.preheader.1, label %for.cond.loopexit.1
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for.body10.preheader.1: ; preds = %for.cond8.preheader.1
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br label %for.body10.1
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for.body10.1: ; preds = %for.body10.1, %for.body10.preheader.1
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%ca.37.1 = phi i64 [ %inc11.1, %for.body10.1 ], [ %ca.2.lcssa.1, %for.body10.preheader.1 ]
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%inc11.1 = add nsw i64 %ca.37.1, 1
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br i1 false, label %for.body10.1, label %for.cond.loopexit.loopexit.1
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for.cond.loopexit.loopexit.1: ; preds = %for.body10.1
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%inc11.lcssa.1 = phi i64 [ %inc11.1, %for.body10.1 ]
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br label %for.cond.loopexit.1
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for.cond.loopexit.1: ; preds = %for.cond.loopexit.loopexit.1, %for.cond8.preheader.1
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%ca.3.lcssa.1 = phi i64 [ %ca.2.lcssa.1, %for.cond8.preheader.1 ], [ %inc11.lcssa.1, %for.cond.loopexit.loopexit.1 ]
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br i1 %cmp, label %for.cond5.preheader.1, label %for.end14.loopexit.1
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for.end14.loopexit.1: ; preds = %for.cond.loopexit.1
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br label %for.end14.1
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for.end14.1: ; preds = %for.end14.loopexit.1, %for.end14
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ret void
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}

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