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Revert r368509 "[CodeGen] Do the Simple Early Return in block-placement pass to optimize the blocks"

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> In `block-placement` pass, it will create some patterns for unconditional we can do the simple early retrun.
> But the `early-ret` pass is before `block-placement`, we don't want to run it again.
> This patch is to do the simple early return to optimize the blocks at the last of `block-placement`.
>
> Reviewed By: efriedma
>
> Differential Revision: https://reviews.llvm.org/D63972

This also revertes follow-ups r368514 and r368532.

llvm-svn: 368560
This commit is contained in:
Hans Wennborg 2019-08-12 12:43:51 +00:00
parent f6ff10d8c4
commit 85ec3cf9ad
3 changed files with 16 additions and 43 deletions
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37
lib/CodeGen/MachineBlockPlacement.cpp
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@ -2755,7 +2755,6 @@ void MachineBlockPlacement::optimizeBranches() {
// cannot because all branches may not be analyzable. // cannot because all branches may not be analyzable.
// E.g., the target may be able to remove an unconditional branch to // E.g., the target may be able to remove an unconditional branch to
// a fallthrough when it occurs after predicated terminators. // a fallthrough when it occurs after predicated terminators.
SmallVector<MachineBasicBlock*, 4> EmptyBB;
for (MachineBasicBlock *ChainBB : FunctionChain) { for (MachineBasicBlock *ChainBB : FunctionChain) {
Cond.clear(); Cond.clear();
MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch. MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
@ -2775,42 +2774,9 @@ void MachineBlockPlacement::optimizeBranches() {
TII->removeBranch(*ChainBB); TII->removeBranch(*ChainBB);
TII->insertBranch(*ChainBB, FBB, TBB, Cond, dl); TII->insertBranch(*ChainBB, FBB, TBB, Cond, dl);
ChainBB->updateTerminator(); ChainBB->updateTerminator();
} else if (Cond.empty() && TBB && ChainBB != TBB &&
!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);
}
for (MachineBasicBlock *Succ : TBB->successors())
ChainBB->addSuccessor(Succ, MBPI->getEdgeProbability(TBB, 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() { void MachineBlockPlacement::alignBlocks() {
@ -3130,9 +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(); optimizeBranches();
alignBlocks(); alignBlocks();

10
test/CodeGen/PowerPC/block-placement-1.mir
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@ -299,8 +299,14 @@ body: |
bb.11.unreachable: bb.11.unreachable:
; CHECK: bb.4.catch4: ; CHECK: bb.4.catch4:
; CHECK: successors: %bb.6(0x00000800) ; CHECK: successors: %bb.11(0x7ffff800), %bb.6(0x00000800)
; CHECK: B %bb.11
; CHECK: bb.1.for.body (align 4): ; CHECK: bb.1.for.body (align 4):
; CHECK: successors: %bb.3(0x00000800) ; CHECK: successors: %bb.2(0x7ffff800), %bb.3(0x00000800)
; CHECK: B %bb.2
; CHECK: bb.2..noexc:
; CHECK: bb.11.unreachable:
... ...

12
test/CodeGen/PowerPC/block-placement.mir
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@ -209,10 +209,14 @@ body: |
BLR8 implicit $lr8, implicit $rm, implicit killed $x3 BLR8 implicit $lr8, implicit $rm, implicit killed $x3
; CHECK: bb.5.if.else.i: ; CHECK: bb.5.if.else.i:
; CHECK-NEXT: renamable $x3 = LI8 1 ; CHECK: successors: %bb.11(0x80000000)
; CHECK-NEXT: BLR8 implicit $lr8, implicit $rm, implicit killed $x3 ; CHECK: B %bb.11
; CHECK: bb.8.while.body.i (align 4): ; CHECK: bb.8.while.body.i (align 4):
; CHECK: successors: %bb.5(0x04000000), %bb.9(0x7c000000) ; CHECK: successors: %bb.11(0x04000000), %bb.9(0x7c000000)
; CHECK: BCC 76, killed renamable $cr0, %bb.5 ; 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
... ...