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MC,AMDGPU: Don't pad .text with s_code_end if it would otherwise be empty #147980

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MC,AMDGPU: Don't pad .text with s_code_end if it would otherwise be empty #147980

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9f4e8e1
AMDGPU: Don't pad .text with s_code_end if it would otherwise be empty
trenouf Feb 20, 2025
dab2b13
Use hasInstructions(), and fix hasInstructions() to work on the asm s…
trenouf Jul 11, 2025
7ab4412
Add test
trenouf Jul 11, 2025
b31739c
Fix setHasInstruction() fix
trenouf Jul 11, 2025
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2 changes: 2 additions & 0 deletions llvm/lib/MC/MCAsmStreamer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2427,6 +2427,8 @@ void MCAsmStreamer::AddEncodingComment(const MCInst &Inst,

void MCAsmStreamer::emitInstruction(const MCInst &Inst,
const MCSubtargetInfo &STI) {
MCStreamer::emitInstruction(Inst, STI);

if (MAI->isAIX() && CurFrag)
// Now that a machine instruction has been assembled into this section, make
// a line entry for any .loc directive that has been seen.
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6 changes: 2 additions & 4 deletions llvm/lib/MC/MCObjectStreamer.cpp
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Expand Up @@ -342,12 +342,10 @@ void MCObjectStreamer::emitInstructionImpl(const MCInst &Inst,
const MCSubtargetInfo &STI) {
MCStreamer::emitInstruction(Inst, STI);

MCSection *Sec = getCurrentSectionOnly();
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emitInstruction is a performance bottleneck. Caution needed when making changes.

getCurrentSectionOnly is efficient. getCurrentSection is not, and the nullness check is redundant. I haven't checked in detail, but adding Sec->setHasInstructions(true); to MCAsmStreamer is likely better .

Sec->setHasInstructions(true);

// Now that a machine instruction has been assembled into this section, make
// a line entry for any .loc directive that has been seen.
MCDwarfLineEntry::make(this, getCurrentSectionOnly());
MCSection *Sec = getCurrentSectionOnly();
MCDwarfLineEntry::make(this, Sec);

// If this instruction doesn't need relaxation, just emit it as data.
MCAssembler &Assembler = getAssembler();
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3 changes: 3 additions & 0 deletions llvm/lib/MC/MCStreamer.cpp
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Expand Up @@ -1194,6 +1194,9 @@ void MCStreamer::visitUsedExpr(const MCExpr &Expr) {
}

void MCStreamer::emitInstruction(const MCInst &Inst, const MCSubtargetInfo &) {
if (MCSection *Sec = getCurrentSection().first)
Sec->setHasInstructions(true);

// Scan for values.
for (unsigned i = Inst.getNumOperands(); i--;)
if (Inst.getOperand(i).isExpr())
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8 changes: 6 additions & 2 deletions llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
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Expand Up @@ -486,12 +486,16 @@ bool AMDGPUAsmPrinter::doFinalization(Module &M) {
// Pad with s_code_end to help tools and guard against instruction prefetch
// causing stale data in caches. Arguably this should be done by the linker,
// which is why this isn't done for Mesa.
// Don't do it if there is no code.
const MCSubtargetInfo &STI = *getGlobalSTI();
if ((AMDGPU::isGFX10Plus(STI) || AMDGPU::isGFX90A(STI)) &&
(STI.getTargetTriple().getOS() == Triple::AMDHSA ||
STI.getTargetTriple().getOS() == Triple::AMDPAL)) {
OutStreamer->switchSection(getObjFileLowering().getTextSection());
getTargetStreamer()->EmitCodeEnd(STI);
MCSection *TextSect = getObjFileLowering().getTextSection();
if (TextSect->hasInstructions()) {
OutStreamer->switchSection(TextSect);
getTargetStreamer()->EmitCodeEnd(STI);
}
}

// Assign expressions which can only be resolved when all other functions are
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9 changes: 9 additions & 0 deletions llvm/test/CodeGen/AMDGPU/empty-text.ll
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@@ -0,0 +1,9 @@
; Test that there is no s_code_end padding if .text is othertwise empty.

; RUN: llc -mtriple=amdgcn--amdpal -mcpu=gfx1200 < %s | FileCheck %s --check-prefixes=GCN

@globalVar = global i32 37

declare amdgpu_ps void @funcDecl()

; GCN-NOT: .fill