[PATCH] D131745: [SCEV] Fix crash in checking the identical of PHI nodes

[Allen zhong via Phabricator via llvm-commits]

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With the commit 20d798b <https://reviews.llvm.org/rG20d798bd47ec5191de1b2a8a031da06a04e612e1>, we generate the node %val_i1_62.lcssa1, which has different
incoming values for the same basic block. But in fact, the two incoming values are equal,
so they should be allowed, eg:

    %val_i1_62.lcssa1 = phi i1 [ %val_i1_52.lcssa2, %bb_3 ], [ %val_i1_52.lcssa3, %bb_3 ]
  label %bb_3
    %val_i1_52.lcssa3 = phi i1 [ %val_i1_52, %bb_2 ]
    %val_i1_52.lcssa2 = phi i1 [ %val_i1_52, %bb_2 ]

Fixes https://github.com/llvm/llvm-project/issues/57000


https://reviews.llvm.org/D131745

Files:
  llvm/lib/IR/Verifier.cpp
  llvm/test/Analysis/ScalarEvolution/pr57000.ll


Index: llvm/test/Analysis/ScalarEvolution/pr57000.ll
===================================================================
--- /dev/null
+++ llvm/test/Analysis/ScalarEvolution/pr57000.ll
@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -indvars -S | FileCheck %s
+
+; Check that it does not crash because the incoming values are equal.
+
+define void @pr57000() {
+; CHECK-LABEL: @pr57000(
+; CHECK-NEXT:  entry_1:
+; CHECK-NEXT:    br label [[BB_2_OUTER:%.*]]
+; CHECK:       bb_2.loopexit:
+; CHECK-NEXT:    br label [[BB_2_OUTER]]
+; CHECK:       bb_2.outer:
+; CHECK-NEXT:    br label [[BB_2:%.*]]
+; CHECK:       bb_2:
+; CHECK-NEXT:    [[VAL_I1_52:%.*]] = icmp sle i64 undef, 2546175499358690212
+; CHECK-NEXT:    br i1 false, label [[BB_2]], label [[BB_3_PREHEADER:%.*]]
+; CHECK:       bb_3.preheader:
+; CHECK-NEXT:    [[VAL_I1_52_LCSSA3:%.*]] = phi i1 [ [[VAL_I1_52]], [[BB_2]] ]
+; CHECK-NEXT:    [[VAL_I1_52_LCSSA2:%.*]] = phi i1 [ [[VAL_I1_52]], [[BB_2]] ]
+; CHECK-NEXT:    br label [[BB_3_OUTER:%.*]]
+; CHECK:       bb_3.outer:
+; CHECK-NEXT:    br label [[BB_3:%.*]]
+; CHECK:       bb_3:
+; CHECK-NEXT:    switch i16 undef, label [[BB_2_LOOPEXIT:%.*]] [
+; CHECK-NEXT:    i16 -1, label [[BB_4:%.*]]
+; CHECK-NEXT:    i16 1, label [[BB_4]]
+; CHECK-NEXT:    i16 4, label [[BB_3]]
+; CHECK-NEXT:    ]
+; CHECK:       bb_4:
+; CHECK-NEXT:    [[VAL_I1_62_LCSSA1:%.*]] = phi i1 [ [[VAL_I1_52_LCSSA2]], [[BB_3]] ], [ [[VAL_I1_52_LCSSA3]], [[BB_3]] ]
+; CHECK-NEXT:    [[VAL_I1_77:%.*]] = icmp ult i1 [[VAL_I1_62_LCSSA1]], undef
+; CHECK-NEXT:    br label [[BB_3_OUTER]]
+;
+entry_1:
+  br label %bb_2
+
+bb_2:                                             ; preds = %bb_3, %bb_2, %entry_1
+  %ptr_i1_13.0 = phi i1 [ undef, %entry_1 ], [ %ptr_i1_13.0, %bb_2 ], [ %ptr_i1_13.1, %bb_3 ]
+  %val_i1_52 = icmp sle i64 undef, 2546175499358690212
+  %val_i8_56 = zext i1 %val_i1_52 to i8
+  br i1 undef, label %bb_2, label %bb_3
+
+bb_3:                                             ; preds = %bb_4, %bb_3, %bb_2
+  %ptr_i1_13.1 = phi i1 [ %ptr_i1_13.0, %bb_2 ], [ %ptr_i1_13.1, %bb_3 ], [ %val_i1_52, %bb_4 ]
+  %val_i1_62 = trunc i8 %val_i8_56 to i1
+  switch i16 undef, label %bb_2 [
+  i16 -1, label %bb_4
+  i16 1, label %bb_4
+  i16 4, label %bb_3
+  ]
+
+bb_4:                                             ; preds = %bb_3, %bb_3
+  %val_i1_77 = icmp ult i1 %val_i1_62, undef
+  br label %bb_3
+}
Index: llvm/lib/IR/Verifier.cpp
===================================================================
--- llvm/lib/IR/Verifier.cpp
+++ llvm/lib/IR/Verifier.cpp
@@ -2740,6 +2740,26 @@
     }
 }
 
+bool isEqualValue(Value *S1, Value *S2) {
+  if (S1 == S2)
+    return true;
+
+  if (isa<PHINode>(S1) && isa<PHINode>(S2)) {
+    const PHINode *PN1 = cast<PHINode>(S1);
+    const PHINode *PN2 = cast<PHINode>(S2);
+    if (PN1->getNumIncomingValues() == PN2->getNumIncomingValues()) {
+      for (unsigned i = 0; i < PN1->getNumIncomingValues(); i++) {
+        if ((PN1->getIncomingValue(i) != PN2->getIncomingValue(i)) ||
+            (PN1->getIncomingBlock(i) != PN2->getIncomingBlock(i)))
+          return false;
+      }
+      return true;
+    }
+  }
+
+  return false;
+}
+
 // verifyBasicBlock - Verify that a basic block is well formed...
 //
 void Verifier::visitBasicBlock(BasicBlock &BB) {
@@ -2774,7 +2794,7 @@
         // all identical.
         //
         Check(i == 0 || Values[i].first != Values[i - 1].first ||
-                  Values[i].second == Values[i - 1].second,
+                  isEqualValue(Values[i].second, Values[i - 1].second),
               "PHI node has multiple entries for the same basic block with "
               "different incoming values!",
               &PN, Values[i].first, Values[i].second, Values[i - 1].second);


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