From: Evan Cheng <evan.cheng@apple.com>
Date: Thu, 23 Sep 2010 06:51:55 +0000 (+0000)
Subject: SDISel should not optimize a unconditional branch following a conditional branch
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=266a99d161069071f32c7c09dded481fd573a82e;p=oota-llvm.git

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 04ac24e9e16..f3bc50d490e 100644
--- 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);
 }