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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 r371177 (git commit f879c6875563c0a8cd838f1e13b14dd33558f1f8)

It caused PR43566 by removing empty, address-taken MachineBasicBlocks.
Such blocks may have references from blockaddress or other operands, and
need more consideration to be removed.

See the PR for a test case to use when relanding.

llvm-svn: 373805
This commit is contained in:
Reid Kleckner 2019-10-04 22:24:21 +00:00
parent 54ad2a4f90
commit 2b0433bae8
2 changed files with 8 additions and 50 deletions
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46
lib/CodeGen/MachineBlockPlacement.cpp
View File

@ -38,7 +38,6 @@
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachinePostDominators.h"
@ -2713,7 +2712,6 @@ 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.
@ -2733,50 +2731,9 @@ 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);
// If TBB was the target of a jump table, update jump tables to go to
// the ChainBB instead.
if (MachineJumpTableInfo *MJTI = F->getJumpTableInfo())
MJTI->ReplaceMBBInJumpTables(TBB, ChainBB);
}
}
}
}
for (auto BB: EmptyBB) {
MLI->removeBlock(BB);
FunctionChain.remove(BB);
BlockToChain.erase(BB);
F->erase(BB);
}
}
void MachineBlockPlacement::alignBlocks() {
@ -3097,9 +3054,6 @@ 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 16):
; 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
...