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[BOLT][BTI] Add MCPlusBuilder::isBTILandingPad #167306

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Merged
merged 2 commits into from
Nov 25, 2025
Merged

[BOLT][BTI] Add MCPlusBuilder::isBTILandingPad #167306

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[BOLT][BTI] Add MCPlusBuilder::isBTILandingPad
bgergely0 Aug 28, 2025
6ee53c8
Fix comment
bgergely0 Nov 25, 2025
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14 changes: 14 additions & 0 deletions bolt/include/bolt/Core/MCPlusBuilder.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1869,6 +1869,20 @@ class MCPlusBuilder {
llvm_unreachable("not implemented");
}

/// Check if an Instruction is a BTI landing pad with the required properties.
/// Takes both explicit and implicit BTIs into account.
virtual bool isBTILandingPad(MCInst &Inst, bool CallTarget,
bool JumpTarget) const {
llvm_unreachable("not implemented");
return false;
}

/// Check if an Instruction is an implicit BTI c landing pad.
virtual bool isImplicitBTIC(MCInst &Inst) const {
llvm_unreachable("not implemented");
return false;
}

/// Create a BTI landing pad instruction.
virtual void createBTI(MCInst &Inst, bool CallTarget, bool JumpTarget) const {
llvm_unreachable("not implemented");
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18 changes: 18 additions & 0 deletions bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
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Expand Up @@ -2782,6 +2782,24 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
Inst.addOperand(MCOperand::createImm(HintNum));
}

bool isBTILandingPad(MCInst &Inst, bool CallTarget,
bool JumpTarget) const override {
unsigned HintNum = getBTIHintNum(CallTarget, JumpTarget);
bool IsExplicitBTI =
Inst.getOpcode() == AArch64::HINT && Inst.getNumOperands() == 1 &&
Inst.getOperand(0).isImm() && Inst.getOperand(0).getImm() == HintNum;

bool IsImplicitBTI = HintNum == 34 && isImplicitBTIC(Inst);
return IsExplicitBTI || IsImplicitBTI;
}

bool isImplicitBTIC(MCInst &Inst) const override {
// PACI[AB]SP are always implicitly BTI C, independently of
// SCTLR_EL1.BT[01].
return Inst.getOpcode() == AArch64::PACIASP ||
Inst.getOpcode() == AArch64::PACIBSP;
}

InstructionListType materializeAddress(const MCSymbol *Target, MCContext *Ctx,
MCPhysReg RegName,
int64_t Addend = 0) const override {
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17 changes: 17 additions & 0 deletions bolt/unittests/Core/MCPlusBuilder.cpp
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Expand Up @@ -155,22 +155,39 @@ TEST_P(MCPlusBuilderTester, AArch64_BTI) {
auto II = BB->begin();
ASSERT_EQ(II->getOpcode(), AArch64::HINT);
ASSERT_EQ(II->getOperand(0).getImm(), 38);
ASSERT_TRUE(BC->MIB->isBTILandingPad(*II, true, true));

MCInst BTIj;
BC->MIB->createBTI(BTIj, false, true);
II = BB->addInstruction(BTIj);
ASSERT_EQ(II->getOpcode(), AArch64::HINT);
ASSERT_EQ(II->getOperand(0).getImm(), 36);
ASSERT_TRUE(BC->MIB->isBTILandingPad(*II, false, true));

MCInst BTIc;
BC->MIB->createBTI(BTIc, true, false);
II = BB->addInstruction(BTIc);
ASSERT_EQ(II->getOpcode(), AArch64::HINT);
ASSERT_EQ(II->getOperand(0).getImm(), 34);
ASSERT_TRUE(BC->MIB->isBTILandingPad(*II, true, false));

MCInst BTIinvalid;
ASSERT_DEATH(BC->MIB->createBTI(BTIinvalid, false, false),
"No target kinds!");

MCInst Paciasp = MCInstBuilder(AArch64::PACIASP);
II = BB->addInstruction(Paciasp);
ASSERT_TRUE(BC->MIB->isBTILandingPad(*II, true, false));
ASSERT_FALSE(BC->MIB->isBTILandingPad(*II, true, true));
ASSERT_FALSE(BC->MIB->isBTILandingPad(*II, false, true));
ASSERT_TRUE(BC->MIB->isImplicitBTIC(*II));

MCInst Pacibsp = MCInstBuilder(AArch64::PACIBSP);
II = BB->addInstruction(Pacibsp);
ASSERT_TRUE(BC->MIB->isBTILandingPad(*II, true, false));
ASSERT_FALSE(BC->MIB->isBTILandingPad(*II, true, true));
ASSERT_FALSE(BC->MIB->isBTILandingPad(*II, false, true));
ASSERT_TRUE(BC->MIB->isImplicitBTIC(*II));
}

TEST_P(MCPlusBuilderTester, AArch64_CmpJNE) {
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5 changes: 3 additions & 2 deletions llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
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Expand Up @@ -150,8 +150,9 @@ void AArch64BranchTargets::addBTI(MachineBasicBlock &MBB, bool CouldCall,
++MBBI)
;

// SCTLR_EL1.BT[01] is set to 0 by default which means
// PACI[AB]SP are implicitly BTI C so no BTI C instruction is needed there.
// PACI[AB]SP are implicitly BTI c so insertion of a BTI can be skipped in
// this case. Depending on the runtime value of SCTLR_EL1.BT[01], they are not
// equivalent to a BTI jc, which still requires an additional BTI.
if (MBBI != MBB.end() && ((HintNum & BTIMask) == BTIC) &&
(MBBI->getOpcode() == AArch64::PACIASP ||
MBBI->getOpcode() == AArch64::PACIBSP))
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