SDISel should not optimize a unconditional branch following a conditional branch

when the unconditional branch destination is the fallthrough block. The
canonicalization makes it easier to allow optimizations on DAGs to invert
conditional branches. The branch folding pass (and AnalyzeBranch) will clean up
the unnecessary unconditional branches later.

This is one of the patches leading up to disabling codegen prepare critical edge
splitting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114630 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 04ac24e9e1630eec892047fb4c88f08aa615fd41..f3bc50d490eedec7a33938cae67bad03d97cb1d5 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1503,10 +1503,11 @@ void SelectionDAGBuilder::visitSwitchCase(CaseBlock &CB,
                                MVT::Other, getControlRoot(), Cond,
                                DAG.getBasicBlock(CB.TrueBB));
 
-  // Insert the false branch.
-  if (CB.FalseBB != NextBlock)
-    BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, BrCond,
-                         DAG.getBasicBlock(CB.FalseBB));
+  // Insert the false branch. Do this even if it's a fall through branch,
+  // this makes it easier to do DAG optimizations which require inverting
+  // the branch condition.
+  BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, BrCond,
+                       DAG.getBasicBlock(CB.FalseBB));
 
   DAG.setRoot(BrCond);
 }