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Enable early elimination of fall-through B in ARM analyzeBranch #152603

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Enable early elimination of fall-through B in ARM analyzeBranch #152603

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17 changes: 17 additions & 0 deletions llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -215,7 +215,24 @@ bool ARMBaseInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
// to clean up any instructions at the tail of the basic block.
CantAnalyze = true;
} else if (isUncondBranchOpcode(I->getOpcode())) {
// Record the fall-through target.
TBB = I->getOperand(0).getMBB();
if (AllowModify && !isPredicated(*I) && TBB &&
MBB.isLayoutSuccessor(TBB)) {
// Remove the fall-through unconditional branch and continue the
// backward scan from the previous instruction. The normal scanning
// logic will classify whatever remains (including fall-through
// conditional branches) consistently with the rest of this function.
auto After = I;
if (After == MBB.instr_begin()) {
I->eraseFromParent();
return false; // Empty of terminators: falls through.
}
auto Prev = std::prev(After);
I->eraseFromParent();
I = Prev;
continue;
}
} else if (isCondBranchOpcode(I->getOpcode())) {
// Bail out if we encounter multiple conditional branches.
if (!Cond.empty())
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1 change: 0 additions & 1 deletion llvm/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
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Expand Up @@ -33,7 +33,6 @@ body: |
; CHECK-NEXT: t2CMPri $sp, 34, 14 /* CC::al */, $noreg, implicit-def $cpsr
; CHECK-NEXT: t2Bcc %bb.2, 1 /* CC::ne */, $cpsr
; CHECK-NEXT: t2Bcc %bb.2, 2 /* CC::hs */, killed $cpsr
; CHECK-NEXT: t2B %bb.1, 14 /* CC::al */, $noreg
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: bb.1:
; CHECK-NEXT: INLINEASM &"", 1 /* sideeffect attdialect */
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