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Don't add CFG edges for redundant conditional branches.

Browse Source 
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.

llvm-svn: 162230
This commit is contained in:
Jakob Stoklund Olesen 2012-08-20 21:39:52 +00:00
parent 5bbc6e5384
commit a3264c242c
3 changed files with 23 additions and 4 deletions
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20
lib/CodeGen/MachineVerifier.cpp
View File

@ -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)) {

5
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -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.

2
test/CodeGen/ARM/constants.ll
View File

@ -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