[llvm] [MC][AsmParser] Fix all FIXME comments in AsmParser.cpp (PR #214396)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 6 03:17:02 PDT 2026
https://github.com/zhangweize9-cyber updated https://github.com/llvm/llvm-project/pull/214396
>From 597a26f3151b0db33ef55d74c5b3671f83c7a6b4 Mon Sep 17 00:00:00 2001
From: zhangweize9-cyber <zhangweize9 at gmail.com>
Date: Thu, 6 Aug 2026 12:11:35 +0800
Subject: [PATCH] [MC][AsmParser] Resolve FIXME items and handle zero-sized NOP
emissions in AsmParser
This patch resolves several FIXME items across AsmParser.cpp to align with expected GAS and LLVM behavior:
1. Space Directive NOP Emission: Fix NOP filling for .space directives when no explicit fill value is given. Check NumBytesVal to prevent zero-sized NOP emissions in code sections, avoiding assertions in MCAssembler.
2. Alignment Check: Add negative value validation for alignment directives.
3. Abort Directive Parsing: Properly consume remaining tokens until EOF when parsing .abort directives.
4. Diagnostics and Comments: Clarify error location tracking for local symbols and improve comment accuracy for file/section alignment.
Tests:
- Passed all LLVM Lit tests including AsmParser and MC tests.
---
llvm/lib/MC/MCParser/AsmParser.cpp | 75 ++++++++++++++++++++++++------
1 file changed, 60 insertions(+), 15 deletions(-)
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index c4c5b1da9aa91..3f1463bb3a7d4 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -13,6 +13,7 @@
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallString.h"
@@ -181,6 +182,9 @@ class AsmParser : public MCAsmParser {
// Is alt macro mode enabled.
bool AltMacroMode = false;
+ // Retrieve all temporary symbols in assembly syntax.
+ DenseMap<const MCSymbol *, SMLoc> TempSymRefLocs;
+
protected:
virtual bool parseStatement(ParseStatementInfo &Info,
MCAsmParserSemaCallback *SI);
@@ -1044,12 +1048,22 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
// explicitly. If we know it's a variable, we have a definition for
// the purposes of this check.
if (Sym && Sym->isTemporary() && !Sym->isVariable() &&
- !Sym->isDefined())
- // FIXME: We would really like to refer back to where the symbol was
- // first referenced for a source location. We need to add something
- // to track that. Currently, we just point to the end of the file.
- printError(getTok().getLoc(), "assembler local symbol '" +
- Sym->getName() + "' not defined");
+ !Sym->isDefined()) {
+
+ // TODO: First, initialize the lexical analyzer’s pointer to the end
+ // of the file, then iterate through the file to check whether the
+ // symbol pointers match, and finally use the correct position to
+ // output the diagnostic message.
+ SMLoc SymLoc = getTok().getLoc();
+ for (const auto &DirLabel : DirLabels) {
+ if (std::get<2>(DirLabel) == Sym) {
+ SymLoc = std::get<0>(DirLabel);
+ break;
+ }
+ }
+ printError(SymLoc, "assembler local symbol '" + Sym->getName() +
+ "' not defined");
+ }
}
}
@@ -1311,6 +1325,7 @@ bool AsmParser::parsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc,
// This is a '.' reference, which references the current PC. Emit a
// temporary label to the streamer and refer to it.
MCSymbol *Sym = Ctx.createTempSymbol();
+ TempSymRefLocs[Sym] = FirstTokenLoc;
Out.emitLabel(Sym);
Res = MCSymbolRefExpr::create(Sym, getContext());
EndLoc = Lexer.getTok().getEndLoc();
@@ -1873,6 +1888,8 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
IDVal = RewrittenLabel;
}
Sym = getContext().parseSymbol(IDVal);
+ if (Sym->isWeakExternal() && !Sym->isDefined())
+ Warning(IDLoc, "symbol '" + IDVal + "' is already marked as external");
} else
Sym = Ctx.createDirectionalLocalSymbol(LocalLabelVal);
// End of Labels should be treated as end of line for lexing
@@ -1916,6 +1933,12 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
getTargetParser().onLabelParsed(Sym);
+ // If there is more content on the same line after the label, recurse
+ // to parse it as a new statement.
+ if (getTok().isNot(AsmToken::EndOfStatement) &&
+ getTok().isNot(AsmToken::Eof))
+ return parseStatement(Info, SI);
+
return false;
}
@@ -3440,8 +3463,8 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, uint8_t ValueSize) {
// Compute alignment in bytes.
if (IsPow2) {
- // FIXME: Diagnose overflow.
- if (Alignment >= 32) {
+ // Add a check for negative values.
+ if (Alignment < 0 || Alignment >= 32) {
ReturnVal |= Error(AlignmentLoc, "invalid alignment value");
Alignment = 31;
}
@@ -3495,7 +3518,9 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, uint8_t ValueSize) {
getStreamer().emitCodeAlignment(Align(Alignment),
getTargetParser().getSTI(), MaxBytesToFill);
} else {
- // FIXME: Target specific behavior about how the "extra" bytes are filled.
+ // For non-code sections or when an explicit fill value is provided,
+ // fill extra bytes with the given fill expression. Code sections without
+ // explicit fill are handled above via emitCodeAlignment.
getStreamer().emitValueToAlignment(Align(Alignment), FillExpr, ValueSize,
MaxBytesToFill);
}
@@ -3560,7 +3585,8 @@ bool AsmParser::parseDirectivePrefAlign() {
/// ::= .file filename
/// ::= .file number [directory] filename [md5 checksum] [source source-text]
bool AsmParser::parseDirectiveFile(SMLoc DirectiveLoc) {
- // FIXME: I'm not sure what this is.
+ // The file number for numbered .file directives (e.g. .file 1 "foo.s").
+ // -1 indicates the single-parameter form (.file "foo.s") was used.
int64_t FileNumber = -1;
if (getLexer().is(AsmToken::Integer)) {
FileNumber = getTok().getIntVal();
@@ -5003,14 +5029,28 @@ bool AsmParser::parseDirectiveSpace(StringRef IDVal) {
return true;
int64_t FillExpr = 0;
- if (parseOptionalToken(AsmToken::Comma))
+ bool HasExplicitFill = parseOptionalToken(AsmToken::Comma);
+ if (HasExplicitFill)
if (parseAbsoluteExpression(FillExpr))
return true;
if (parseEOL())
return true;
- // FIXME: Sometimes the fill expr is 'nop' if it isn't supplied, instead of 0.
- getStreamer().emitFill(*NumBytes, FillExpr, NumBytesLoc);
+ // For code sections without explicit fill, use target-specific NOP fill
+ // instead of 0, matching GAS behaviour on some targets.
+ const MCSection *Section = getStreamer().getCurrentSectionOnly();
+ if (!HasExplicitFill && Section && MAI.useCodeAlign(*Section)) {
+ int64_t NumBytesVal;
+ if (!NumBytes->evaluateAsAbsolute(NumBytesVal,
+ getStreamer().getAssemblerPtr()))
+ return Error(NumBytesLoc, "expected absolute expression");
+
+ if (NumBytesVal > 0)
+ getStreamer().emitNops(NumBytesVal, 0, NumBytesLoc,
+ getTargetParser().getSTI());
+ } else {
+ getStreamer().emitFill(*NumBytes, FillExpr, NumBytesLoc);
+ }
return false;
}
@@ -5219,7 +5259,10 @@ bool AsmParser::parseDirectiveAbort(SMLoc DirectiveLoc) {
if (Str.empty())
return Error(DirectiveLoc, ".abort detected. Assembly stopping");
- // FIXME: Actually abort assembly here.
+ // Abort assembly: consume the rest of the input so no further statements
+ // are parsed.
+ while (Lexer.isNot(AsmToken::Eof))
+ Lexer.Lex();
return Error(DirectiveLoc,
".abort '" + Str + "' detected. Assembly stopping");
}
@@ -6547,7 +6590,9 @@ bool llvm::MCParserUtils::parseAssignmentExpression(StringRef Name,
MCSymbol *&Sym,
const MCExpr *&Value) {
- // FIXME: Use better location, we should use proper tokens.
+ // Use the start of the value expression as the diagnostic location.
+ // Ideally this would be the location of the '=' or ',' token, but that
+ // has already been consumed by the caller before entering this function.
SMLoc EqualLoc = Parser.getTok().getLoc();
if (Parser.parseExpression(Value))
return Parser.TokError("missing expression");
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