[llvm] r192001 - UpdatePHINodes in BasicBlockUtils should not crash on duplicate predecessors

[Hal Finkel]

Author: hfinkel
Date: Fri Oct  4 18:41:05 2013
New Revision: 192001

URL: http://llvm.org/viewvc/llvm-project?rev=192001&view=rev
Log:
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).

Added:
    llvm/trunk/test/Transforms/LoopSimplify/dup-preds.ll
Modified:
    llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp

Modified: llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp?rev=192001&r1=192000&r2=192001&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp Fri Oct  4 18:41:05 2013
@@ -400,8 +400,12 @@ static void UpdatePHINodes(BasicBlock *O
       // 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

Added: llvm/trunk/test/Transforms/LoopSimplify/dup-preds.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSimplify/dup-preds.ll?rev=192001&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopSimplify/dup-preds.ll (added)
+++ llvm/trunk/test/Transforms/LoopSimplify/dup-preds.ll Fri Oct  4 18:41:05 2013
@@ -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 }
+