[llvm-commits] [llvm] r162230 - in /llvm/trunk: lib/CodeGen/MachineVerifier.cpp lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp test/CodeGen/ARM/constants.ll

[Jakob Stoklund Olesen]

Author: stoklund
Date: Mon Aug 20 16:39:52 2012
New Revision: 162230

URL: http://llvm.org/viewvc/llvm-project?rev=162230&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/CodeGen/MachineVerifier.cpp
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    llvm/trunk/test/CodeGen/ARM/constants.ll

Modified: llvm/trunk/lib/CodeGen/MachineVerifier.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineVerifier.cpp?rev=162230&r1=162229&r2=162230&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineVerifier.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineVerifier.cpp Mon Aug 20 16:39:52 2012
@@ -580,7 +580,15 @@
       ++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 @@
     } 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)) {

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=162230&r1=162229&r2=162230&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Mon Aug 20 16:39:52 2012
@@ -1601,7 +1601,10 @@
 
   // 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.

Modified: llvm/trunk/test/CodeGen/ARM/constants.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/constants.ll?rev=162230&r1=162229&r2=162230&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/constants.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/constants.ll Mon Aug 20 16:39:52 2012
@@ -1,4 +1,4 @@
-; RUN: llc < %s -mtriple=armv4t-unknown-linux-gnueabi -disable-cgp-branch-opts | FileCheck %s
+; RUN: llc < %s -mtriple=armv4t-unknown-linux-gnueabi -disable-cgp-branch-opts -verify-machineinstrs | FileCheck %s
 
 define i32 @f1() {
 ; CHECK: f1