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Revert "[CodeGen] Do the Simple Early Return in block-placement pass to optimize the blocks"

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This reverts commit b3d258fc44b588f06eb35f8e4b9a6d1fc859acec.

@skatkov is reporting crash in D63972#1646303
Contacted @ZhangKang, and revert the commit on behalf of him.

llvm-svn: 370069
This commit is contained in:
Jinsong Ji 2019-08-27 14:59:08 +00:00
parent 4210f9b69b
commit d7a719014a
2 changed files with 8 additions and 44 deletions
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40
lib/CodeGen/MachineBlockPlacement.cpp
View File

@ -2755,7 +2755,6 @@ void MachineBlockPlacement::optimizeBranches() {
// cannot because all branches may not be analyzable.
// E.g., the target may be able to remove an unconditional branch to
// a fallthrough when it occurs after predicated terminators.
SmallVector<MachineBasicBlock*, 4> EmptyBB;
for (MachineBasicBlock *ChainBB : FunctionChain) {
Cond.clear();
MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
@ -2775,45 +2774,9 @@ void MachineBlockPlacement::optimizeBranches() {
TII->removeBranch(*ChainBB);
TII->insertBranch(*ChainBB, FBB, TBB, Cond, dl);
ChainBB->updateTerminator();
} else if (Cond.empty() && TBB && ChainBB != TBB && !TBB->empty() &&
!TBB->canFallThrough()) {
// When ChainBB is unconditional branch to the TBB, and TBB has no
// fallthrough predecessor and fallthrough successor, try to merge
// ChainBB and TBB. This is legal under the one of following conditions:
// 1. ChainBB is empty except for an unconditional branch.
// 2. TBB has only one predecessor.
MachineFunction::iterator I(TBB);
if (((TBB == &*F->begin()) || !std::prev(I)->canFallThrough()) &&
(TailDup.isSimpleBB(ChainBB) || (TBB->pred_size() == 1))) {
TII->removeBranch(*ChainBB);
ChainBB->removeSuccessor(TBB);
// Update the CFG.
while (!TBB->pred_empty()) {
MachineBasicBlock *Pred = *(TBB->pred_end() - 1);
Pred->ReplaceUsesOfBlockWith(TBB, ChainBB);
}
while (!TBB->succ_empty()) {
MachineBasicBlock *Succ = *(TBB->succ_end() - 1);
ChainBB->addSuccessor(Succ, MBPI->getEdgeProbability(TBB, Succ));
TBB->removeSuccessor(Succ);
}
// Move all the instructions of TBB to ChainBB.
ChainBB->splice(ChainBB->end(), TBB, TBB->begin(), TBB->end());
EmptyBB.push_back(TBB);
}
}
}
}
for (auto BB: EmptyBB) {
MLI->removeBlock(BB);
FunctionChain.remove(BB);
BlockToChain.erase(BB);
F->erase(BB);
}
}
void MachineBlockPlacement::alignBlocks() {
@ -3133,9 +3096,6 @@ bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &MF) {
}
}
// optimizeBranches() may change the blocks, but we haven't updated the
// post-dominator tree. Because the post-dominator tree won't be used after
// this function and this pass don't preserve the post-dominator tree.
optimizeBranches();
alignBlocks();

12
test/CodeGen/PowerPC/block-placement.mir
View File

@ -209,10 +209,14 @@ body: |
BLR8 implicit $lr8, implicit $rm, implicit killed $x3
; CHECK: bb.5.if.else.i:
; CHECK-NEXT: renamable $x3 = LI8 1
; CHECK-NEXT: BLR8 implicit $lr8, implicit $rm, implicit killed $x3
; CHECK: successors: %bb.11(0x80000000)
; CHECK: B %bb.11
; CHECK: bb.8.while.body.i (align 4):
; CHECK: successors: %bb.5(0x04000000), %bb.9(0x7c000000)
; CHECK: BCC 76, killed renamable $cr0, %bb.5
; CHECK: successors: %bb.11(0x04000000), %bb.9(0x7c000000)
; CHECK: BCC 76, killed renamable $cr0, %bb.11
; CHECK: bb.11:
; CHECK: renamable $x3 = LI8 1
; CHECK-NEXT: BLR8 implicit $lr8, implicit $rm, implicit killed $x3
...