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[PowerPC] Do the Simple Early Return in block-placement pass to optimize the blocks

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Summary:
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`. 

Below is an example
```
BB:                   | BB:
   XOR 3, 3, 4        |   XOR 3, 3, 4
   B TBB              |   B ChainBB
...                   | ...
ChainBB:              | ChainBB:
   B TBB              |   ADD 3, 3, 4
...                   |   BLR
TBB:                  |
   ADD 3, 3, 4        |
   BLR                |
```

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D63972

llvm-svn: 367080
This commit is contained in:
Kang Zhang 2019-07-26 01:58:53 +00:00
parent 0dce6b4c97
commit 207303b4af
3 changed files with 31 additions and 16 deletions
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25
lib/CodeGen/MachineBlockPlacement.cpp
View File

@ -2730,6 +2730,31 @@ 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.
for (MachineBasicBlock::pred_iterator PI = TBB->pred_begin(),
PE = TBB->pred_end(); PI != PE; PI++)
(*PI)->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());
F->remove(TBB);
}
} }
} }
} }

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

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

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