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

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);

test/CodeGen/PowerPC/bdzlr.ll

@@ -53,6 +53,7 @@ for.end:                                          ; preds = %for.body, %if.end,
 ; CHECK: bnelr
 ; CHECK: bnelr
 ; CHECK: bdzlr
+; CHECK-NOT: blr
 }
 
 attributes #0 = { nounwind }

test/CodeGen/PowerPC/early-ret2.ll

@@ -17,7 +17,6 @@ while.end:                                        ; preds = %while.body, %while.
 
 ; CHECK: @_Z8example3iPiS_
 ; CHECK: bnelr
-; CHECK: bnelr
 }
 
 attributes #0 = { noinline nounwind }