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Fix tail merging to assign the (more) correct BasicBlock when splitting.

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This makes it possible to write unit tests that are less susceptible
to minor code motion, particularly copy placement. block-placement.ll
covers this case with -pre-RA-sched=source which will soon be
default. One incorrectly named block is already fixed, but without
this fix, enabling new coalescing and scheduling would cause more
failures.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184680 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2013-06-24 01:55:01 +00:00
parent 722b0a4d29
commit f7b5e01636
3 changed files with 16 additions and 7 deletions
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15
lib/CodeGen/BranchFolding.cpp
View File

@ -406,7 +406,8 @@ void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
/// MBB so that the part before the iterator falls into the part starting at the
/// iterator. This returns the new MBB.
MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
MachineBasicBlock::iterator BBI1) {
MachineBasicBlock::iterator BBI1,
const BasicBlock *BB) {
if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1))
return 0;
@ -414,7 +415,7 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
// Create the fall-through block.
MachineFunction::iterator MBBI = &CurMBB;
MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(CurMBB.getBasicBlock());
MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(BB);
CurMBB.getParent()->insert(++MBBI, NewMBB);
// Move all the successors of this block to the specified block.
@ -647,6 +648,7 @@ void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
/// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist
/// only of the common tail. Create a block that does by splitting one.
bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
MachineBasicBlock *SuccBB,
unsigned maxCommonTailLength,
unsigned &commonTailIndex) {
commonTailIndex = 0;
@ -676,7 +678,12 @@ bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
DEBUG(dbgs() << "\nSplitting BB#" << MBB->getNumber() << ", size "
<< maxCommonTailLength);
MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI);
// If the split block unconditionally falls-thru to SuccBB, it will be
// merged. In control flow terms it should then take SuccBB's name. e.g. If
// SuccBB is an inner loop, the common tail is still part of the inner loop.
const BasicBlock *BB = (SuccBB && MBB->succ_size() == 1) ?
SuccBB->getBasicBlock() : MBB->getBasicBlock();
MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI, BB);
if (!newMBB) {
DEBUG(dbgs() << "... failed!");
return false;
@ -784,7 +791,7 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
!SameTails[commonTailIndex].tailIsWholeBlock())) {
// None of the blocks consist entirely of the common tail.
// Split a block so that one does.
if (!CreateCommonTailOnlyBlock(PredBB,
if (!CreateCommonTailOnlyBlock(PredBB, SuccBB,
maxCommonTailLength, commonTailIndex)) {
RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
continue;

4
lib/CodeGen/BranchFolding.h
View File

@ -100,13 +100,15 @@ namespace llvm {
void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
MachineBasicBlock *NewDest);
MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
MachineBasicBlock::iterator BBI1);
MachineBasicBlock::iterator BBI1,
const BasicBlock *BB);
unsigned ComputeSameTails(unsigned CurHash, unsigned minCommonTailLength,
MachineBasicBlock *SuccBB,
MachineBasicBlock *PredBB);
void RemoveBlocksWithHash(unsigned CurHash, MachineBasicBlock* SuccBB,
MachineBasicBlock* PredBB);
bool CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
MachineBasicBlock *SuccBB,
unsigned maxCommonTailLength,
unsigned &commonTailIndex);

4
test/CodeGen/X86/block-placement.ll
View File

@ -1,4 +1,4 @@
; RUN: llc -mtriple=i686-linux < %s | FileCheck %s
; RUN: llc -mtriple=i686-linux -pre-RA-sched=source < %s | FileCheck %s
declare void @error(i32 %i, i32 %a, i32 %b)
@ -997,7 +997,7 @@ define void @benchmark_heapsort(i32 %n, double* nocapture %ra) {
; CHECK: %while.body
; CHECK: %land.lhs.true
; CHECK: %if.then19
; CHECK: %if.then19
; CHECK: %if.end20
; CHECK: %if.then8
; CHECK: ret