[LoopBoundSplit] Update phi node in exit block

[jaykang10]

Summary

This patch updates phi node in exit block properly.

It fixes https://bugs.llvm.org/show_bug.cgi?id=51700

[reames]

LGTM

[jaykang10]

In D109160#2980001, @reames wrote:

LGTM

Thanks for review @reames! Let me push this change.

[bjope]

In D109160#2981670, @jaykang10 wrote:

In D109160#2980001, @reames wrote:

LGTM

Thanks for review @reames! Let me push this change.

Thanks for looking into the PR @jaykang10 . I'll rerun my test cases when this has landed!

[jaykang10]

In D109160#2981685, @bjope wrote:

In D109160#2981670, @jaykang10 wrote:

In D109160#2980001, @reames wrote:

LGTM

Thanks for review @reames! Let me push this change.

Thanks for looking into the PR @jaykang10 . I'll rerun my test cases when this has landed!

Thanks for checking this pass. @bjope

I have pushed this change. If there is still something wrong with the pass, please let me know.

[jaykang10]

562521e2d15aff38587aef8c6ea1baf3ed87513c

[jaykang10]

In D109160#2981686, @jaykang10 wrote:

In D109160#2981685, @bjope wrote:

In D109160#2981670, @jaykang10 wrote:

In D109160#2980001, @reames wrote:

LGTM

Thanks for review @reames! Let me push this change.

Thanks for looking into the PR @jaykang10 . I'll rerun my test cases when this has landed!

Thanks for checking this pass. @bjope

I have pushed this change. If there is still something wrong with the pass, please let me know.

@bjope From your email on llvm-dev, I can see you try to use loop-distribute pass. If possible, can I ask you have plan to enable the pass as default in upstream please?

llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp

 //===------- LoopBoundSplit.cpp - Split Loop Bound --------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Scalar/LoopBoundSplit.h"
+#include "llvm/ADT/Sequence.h"
 #include "llvm/Analysis/LoopAccessAnalysis.h"
 #include "llvm/Analysis/LoopAnalysisManager.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopIterator.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/ScalarEvolution.h"
static bool splitLoopBound(Loop &L, DominatorTree &DT, LoopInfo &LI,
   ClonedSplitCandidateBI->setCondition(ConstantInt::getFalse(Context));
 
   // Replace exit branch target of pre-loop by post-loop's preheader.
   if (L.getExitBlock() == ExitingCond.BI->getSuccessor(0))
     ExitingCond.BI->setSuccessor(0, PostLoopPreHeader);
   else
     ExitingCond.BI->setSuccessor(1, PostLoopPreHeader);
 
+  // Update phi node in exit block of post-loop.
+  for (PHINode &PN : PostLoop->getExitBlock()->phis()) {
+    for (auto i : seq<int>(0, PN.getNumOperands())) {
+      // Check incoming block is pre-loop's exiting block.
+      if (PN.getIncomingBlock(i) == L.getExitingBlock()) {
+        // Replace pre-loop's exiting block by post-loop's preheader.
+        PN.setIncomingBlock(i, PostLoopPreHeader);
+        // Add a new incoming value with post-loop's exiting block.
+        PN.addIncoming(VMap[PN.getIncomingValue(i)],
+                       PostLoop->getExitingBlock());
+      }
+    }
+  }
+
   // Update dominator tree.
   DT.changeImmediateDominator(PostLoopPreHeader, L.getExitingBlock());
   DT.changeImmediateDominator(PostLoop->getExitBlock(), PostLoopPreHeader);
 
   // Invalidate cached SE information.
   SE.forgetLoop(&L);
 
   // Canonicalize loops.

llvm/test/Transforms/LoopBoundSplit/bug-loop-bound-split-phi-in-exit-block.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=loop-bound-split -S < %s | FileCheck %s
+
+; Previously, it caused compiler crash from verifier.
+; The phi node in exit block should be updated properly.
+
+define i16 @test_int() {
+; CHECK-LABEL: @test_int(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[ENTRY_SPLIT:%.*]]
+; CHECK:       entry.split:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[I:%.*]] = phi i16 [ 0, [[ENTRY_SPLIT]] ], [ [[ADD:%.*]], [[COND_END:%.*]] ]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i16 [[I]], 3
+; CHECK-NEXT:    br i1 true, label [[COND_TRUE:%.*]], label [[COND_FALSE:%.*]]
+; CHECK:       cond.true:
+; CHECK-NEXT:    br label [[COND_END]]
+; CHECK:       cond.false:
+; CHECK-NEXT:    br label [[COND_END]]
+; CHECK:       cond.end:
+; CHECK-NEXT:    [[CALL:%.*]] = call i16 @foo()
+; CHECK-NEXT:    [[ADD]] = add nuw nsw i16 [[I]], 1
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp ult i16 [[I]], 3
+; CHECK-NEXT:    br i1 [[CMP2]], label [[FOR_BODY]], label [[ENTRY_SPLIT_SPLIT:%.*]]
+; CHECK:       entry.split.split:
+; CHECK-NEXT:    [[CALL_LCSSA1:%.*]] = phi i16 [ [[CALL]], [[COND_END]] ]
+; CHECK-NEXT:    [[I_LCSSA:%.*]] = phi i16 [ [[I]], [[COND_END]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ne i16 [[I_LCSSA]], 11
+; CHECK-NEXT:    br i1 [[TMP0]], label [[FOR_BODY_SPLIT_PREHEADER:%.*]], label [[END:%.*]]
+; CHECK:       for.body.split.preheader:
+; CHECK-NEXT:    br label [[FOR_BODY_SPLIT:%.*]]
+; CHECK:       for.body.split:
+; CHECK-NEXT:    [[I_SPLIT:%.*]] = phi i16 [ [[ADD_SPLIT:%.*]], [[COND_END_SPLIT:%.*]] ], [ 0, [[FOR_BODY_SPLIT_PREHEADER]] ]
+; CHECK-NEXT:    [[CMP1_SPLIT:%.*]] = icmp ult i16 [[I_SPLIT]], 3
+; CHECK-NEXT:    br i1 false, label [[COND_TRUE_SPLIT:%.*]], label [[COND_FALSE_SPLIT:%.*]]
+; CHECK:       cond.false.split:
+; CHECK-NEXT:    br label [[COND_END_SPLIT]]
+; CHECK:       cond.true.split:
+; CHECK-NEXT:    br label [[COND_END_SPLIT]]
+; CHECK:       cond.end.split:
+; CHECK-NEXT:    [[CALL_SPLIT:%.*]] = call i16 @foo()
+; CHECK-NEXT:    [[ADD_SPLIT]] = add nuw nsw i16 [[I_SPLIT]], 1
+; CHECK-NEXT:    [[CMP2_SPLIT:%.*]] = icmp ult i16 [[I_SPLIT]], 11
+; CHECK-NEXT:    br i1 [[CMP2_SPLIT]], label [[FOR_BODY_SPLIT]], label [[END_LOOPEXIT:%.*]]
+; CHECK:       end.loopexit:
+; CHECK-NEXT:    [[CALL_LCSSA_PH:%.*]] = phi i16 [ [[CALL_SPLIT]], [[COND_END_SPLIT]] ]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[CALL_LCSSA:%.*]] = phi i16 [ [[CALL_LCSSA1]], [[ENTRY_SPLIT_SPLIT]] ], [ [[CALL_LCSSA_PH]], [[END_LOOPEXIT]] ]
+; CHECK-NEXT:    ret i16 [[CALL_LCSSA]]
+;
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %cond.end
+  %i = phi i16 [ 0, %entry ], [ %add, %cond.end ]
+  %cmp1 = icmp ult i16 %i, 3
+  br i1 %cmp1, label %cond.true, label %cond.false
+
+cond.true:                                        ; preds = %for.body
+  br label %cond.end
+
+cond.false:                                       ; preds = %for.body
+  br label %cond.end
+
+cond.end:                                         ; preds = %cond.false, %cond.true
+  %call = call i16 @foo()
+  %add = add nuw nsw i16 %i, 1
+  %cmp2 = icmp ult i16 %i, 11
+  br i1 %cmp2, label %for.body, label %end
+
+end:                                              ; preds = %cond.end
+  ret i16 %call
+}
+
+declare i16 @foo()