From e7fdef420d0c8a825555d246da259342c48bd527 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Mon, 20 Aug 2012 21:39:52 +0000
Subject: [PATCH] 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
---
lib/CodeGen/MachineVerifier.cpp | 20 +++++++++++++++++--
.../SelectionDAG/SelectionDAGBuilder.cpp | 5 ++++-
test/CodeGen/ARM/constants.ll | 2 +-
3 files changed, 23 insertions(+), 4 deletions(-)
diff --git a/lib/CodeGen/MachineVerifier.cpp b/lib/CodeGen/MachineVerifier.cpp
index f3e310ca3e0..852c169254d 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 ae2b32969a7..f3cf7582be3 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.
diff --git a/test/CodeGen/ARM/constants.ll b/test/CodeGen/ARM/constants.ll
index f4c1b5acef9..0ac8b48d390 100644
--- a/test/CodeGen/ARM/constants.ll
+++ b/test/CodeGen/ARM/constants.ll
@@ -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