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[BOLT] Do not use HLT as split point when build the CFG #150963

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Merged
merged 1 commit into from
Aug 15, 2025
+29 −2
Merged

[BOLT] Do not use HLT as split point when build the CFG #150963

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4 changes: 4 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 @@ -740,6 +740,10 @@ class MCPlusBuilder {
return false;
}

/// Return true if the hlt instruction under the x86, otherwise, default to
/// false.
virtual bool isX86HLT(const MCInst &Inst) const { return false; }

/// Return the width, in bytes, of the memory access performed by \p Inst, if
/// this is a pop instruction. Return zero otherwise.
virtual int getPopSize(const MCInst &Inst) const {
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6 changes: 4 additions & 2 deletions bolt/lib/Core/MCPlusBuilder.cpp
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Expand Up @@ -132,8 +132,10 @@ bool MCPlusBuilder::equals(const MCSpecifierExpr &A, const MCSpecifierExpr &B,
}

bool MCPlusBuilder::isTerminator(const MCInst &Inst) const {
return Analysis->isTerminator(Inst) ||
(opts::TerminalTrap && Info->get(Inst.getOpcode()).isTrap());
return (opts::TerminalTrap && Info->get(Inst.getOpcode()).isTrap()) ||
Analysis->isTerminator(Inst)
? !isX86HLT(Inst)
: false;
}

void MCPlusBuilder::setTailCall(MCInst &Inst) const {
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4 changes: 4 additions & 0 deletions bolt/lib/Target/X86/X86MCPlusBuilder.cpp
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Expand Up @@ -223,6 +223,10 @@ class X86MCPlusBuilder : public MCPlusBuilder {
return Inst.getOpcode() == X86::ENDBR32 || Inst.getOpcode() == X86::ENDBR64;
}

bool isX86HLT(const MCInst &Inst) const override {
return Inst.getOpcode() == X86::HLT;
}

int getPopSize(const MCInst &Inst) const override {
switch (Inst.getOpcode()) {
case X86::POP16r:
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17 changes: 17 additions & 0 deletions bolt/test/X86/cfg_build_hlt.s
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@@ -0,0 +1,17 @@
## Check CFG for halt instruction

# RUN: %clang %cflags %s -static -o %t.exe -nostdlib
# RUN: llvm-bolt %t.exe --print-cfg --print-only=main -o %t 2>&1 | FileCheck %s --check-prefix=CHECK-CFG
# RUN: llvm-objdump -d %t --print-imm-hex | FileCheck %s --check-prefix=CHECK-BIN

# CHECK-CFG: BB Count : 1
# CHECK-BIN: <main>:
# CHECK-BIN-NEXT: f4 hlt
# CHECK-BIN-NEXT: c3 retq

.global main
.type main, %function
main:
hlt
retq
.size main, .-main
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