UpdatePHINodes in BasicBlockUtils should not crash on duplicate predecessors

UpdatePHINodes has an optimization to reuse an existing PHI node, where it
first deletes all of its entries and then replaces them. Unfortunately, in the
case where we had duplicate predecessors (which are allowed so long as the
associated PHI entries have the same value), the loop removing the existing PHI
entries from the to-be-reused PHI would assert (if that PHI was not the one
which had the duplicates).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192001 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index a2e82f337b9dba5e68bf8046f26ce98ca6ff602b..12de9eed4b85e503eca66f112d6e14c7c308d013 100644 (file)
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -400,8 +400,12 @@ static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
       // If all incoming values for the new PHI would be the same, just don't
       // make a new PHI.  Instead, just remove the incoming values from the old
       // PHI.
-      for (unsigned i = 0, e = Preds.size(); i != e; ++i)
-        PN->removeIncomingValue(Preds[i], false);
+      for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
+        // Explicitly check the BB index here to handle duplicates in Preds.
+        int Idx = PN->getBasicBlockIndex(Preds[i]);
+        if (Idx >= 0)
+          PN->removeIncomingValue(Idx, false);
+      }
     } else {
       // If the values coming into the block are not the same, we need a PHI.
       // Create the new PHI node, insert it into NewBB at the end of the block

diff --git a/test/Transforms/LoopSimplify/dup-preds.ll b/test/Transforms/LoopSimplify/dup-preds.ll
new file mode 100644 (file)
index 0000000..3d1f149
--- /dev/null
+++ b/test/Transforms/LoopSimplify/dup-preds.ll
@@ -0,0 +1,46 @@
+; RUN: opt -loop-simplify -S %s | FileCheck %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-bgq-linux"
+
+define fastcc void @do_update_md([3 x float]* nocapture readonly %x) #0 {
+entry:
+  br i1 undef, label %if.end365, label %lor.lhs.false134
+
+lor.lhs.false134:                                 ; preds = %entry
+  br i1 undef, label %lor.lhs.false138, label %if.end365
+
+lor.lhs.false138:                                 ; preds = %lor.lhs.false134
+  br i1 undef, label %lor.lhs.false142, label %if.end365
+
+lor.lhs.false142:                                 ; preds = %lor.lhs.false138
+  br i1 undef, label %for.body276.lr.ph, label %if.end365
+
+for.body276.lr.ph:                                ; preds = %lor.lhs.false142
+  switch i16 undef, label %if.then288 [
+    i16 4, label %for.body344
+    i16 2, label %for.body344
+  ]
+
+if.then288:                                       ; preds = %for.body276.lr.ph
+  br label %for.body305
+
+for.body305:                                      ; preds = %for.body305, %if.then288
+  br label %for.body305
+
+for.body344:                                      ; preds = %for.body344, %for.body276.lr.ph, %for.body276.lr.ph
+  %indvar = phi i64 [ %indvar.next, %for.body344 ], [ 0, %for.body276.lr.ph ]
+  %indvars.iv552 = phi i64 [ %indvars.iv.next553, %for.body344 ], [ 0, %for.body276.lr.ph ], [ 0, %for.body276.lr.ph ]
+  %indvars.iv.next553 = add nuw nsw i64 %indvars.iv552, 1
+  %indvar.next = add i64 %indvar, 1
+  br label %for.body344
+
+; CHECK-LABEL: @do_update_md
+; CHECK: %indvars.iv552 = phi i64 [ %indvars.iv.next553, %for.body344 ], [ 0, %for.body344.preheader ]
+; CHECK: ret
+
+if.end365:                                        ; preds = %lor.lhs.false142, %lor.lhs.false138, %lor.lhs.false134, %entry
+  ret void
+}
+
+attributes #0 = { nounwind }
+