Don't add CFG edges for redundant conditional branches.

IR that hasn't been through SimplifyCFG can look like this:

  br i1 %b, label %r, label %r

Make sure we don't create duplicate Machine CFG edges in this case.

Fix the machine code verifier to accept conditional branches with a
single CFG edge.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162230 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 22 insertions, 3 deletions

diff --git a/lib/CodeGen/MachineVerifier.cpp b/lib/CodeGen/MachineVerifier.cpp
index f3e310c..852c169 100644
--- a/lib/CodeGen/MachineVerifier.cpp
+++ b/lib/CodeGen/MachineVerifier.cpp
@@ -580,7 +580,15 @@ MachineVerifier::visitMachineBasicBlockBefore(const MachineBasicBlock *MBB) {
       ++MBBI;
       if (MBBI == MF->end()) {
         report("MBB conditionally falls through out of function!", MBB);
-      } if (MBB->succ_size() != 2) {
+      } if (MBB->succ_size() == 1) {
+        // A conditional branch with only one successor is weird, but allowed.
+        if (&*MBBI != TBB)
+          report("MBB exits via conditional branch/fall-through but only has "
+                 "one CFG successor!", MBB);
+        else if (TBB != *MBB->succ_begin())
+          report("MBB exits via conditional branch/fall-through but the CFG "
+                 "successor don't match the actual successor!", MBB);
+      } else if (MBB->succ_size() != 2) {
         report("MBB exits via conditional branch/fall-through but doesn't have "
                "exactly two CFG successors!", MBB);
       } else if (!matchPair(MBB->succ_begin(), TBB, MBBI)) {
@@ -600,7 +608,15 @@ MachineVerifier::visitMachineBasicBlockBefore(const MachineBasicBlock *MBB) {
     } else if (TBB && FBB) {
       // Block conditionally branches somewhere, otherwise branches
       // somewhere else.
-      if (MBB->succ_size() != 2) {
+      if (MBB->succ_size() == 1) {
+        // A conditional branch with only one successor is weird, but allowed.
+        if (FBB != TBB)
+          report("MBB exits via conditional branch/branch through but only has "
+                 "one CFG successor!", MBB);
+        else if (TBB != *MBB->succ_begin())
+          report("MBB exits via conditional branch/branch through but the CFG "
+                 "successor don't match the actual successor!", MBB);
+      } else if (MBB->succ_size() != 2) {
         report("MBB exits via conditional branch/branch but doesn't have "
                "exactly two CFG successors!", MBB);
       } else if (!matchPair(MBB->succ_begin(), TBB, FBB)) {
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index ae2b329..f3cf758 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1601,7 +1601,10 @@ void SelectionDAGBuilder::visitSwitchCase(CaseBlock &CB,
 
   // Update successor info
   addSuccessorWithWeight(SwitchBB, CB.TrueBB, CB.TrueWeight);
-  addSuccessorWithWeight(SwitchBB, CB.FalseBB, CB.FalseWeight);
+  // TrueBB and FalseBB are always different unless the incoming IR is
+  // degenerate. This only happens when running llc on weird IR.
+  if (CB.TrueBB != CB.FalseBB)
+    addSuccessorWithWeight(SwitchBB, CB.FalseBB, CB.FalseWeight);
 
   // Set NextBlock to be the MBB immediately after the current one, if any.
   // This is used to avoid emitting unnecessary branches to the next block.