Manually remove successors in if conversion when CopyAndPredicateBlock is used

In the simple and triangle if-conversion cases, when CopyAndPredicateBlock is
used because the to-be-predicated block has other predecessors, we need to
explicitly remove the old copied block from the successors list. Normally if
conversion relies on TII->AnalyzeBranch combined with BB->CorrectExtraCFGEdges
to cleanup the successors list, but if the predicated block contained an
un-analyzable branch (such as a now-predicated return), then this will fail.

These extra successors were causing a problem on PPC because it was causing
later passes (such as PPCEarlyReturm) to leave dead return-only basic blocks in
the code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179227 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index 9958d7daad..eaff93fd7f 100644
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -1054,6 +1054,10 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
     // Copy instructions in the true block, predicate them, and add them to
     // the entry block.
     CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs);
+
+    // RemoveExtraEdges won't work if the block has an unanalyzable branch, so
+    // explicitly remove CvtBBI as a successor.
+    BBI.BB->removeSuccessor(CvtBBI->BB);
   } else {
     PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
 
@@ -1146,6 +1150,10 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
     // Copy instructions in the true block, predicate them, and add them to
     // the entry block.
     CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, true);
+
+    // RemoveExtraEdges won't work if the block has an unanalyzable branch, so
+    // explicitly remove CvtBBI as a successor.
+    BBI.BB->removeSuccessor(CvtBBI->BB);
   } else {
     // Predicate the 'true' block after removing its branch.
     CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);