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llvm-project/llvm/lib/MC/MCExpr.cpp
Fangrui Song 36978fadb8 [MC] Add UseAtForSpecifier 
Some ELF targets don't use @ for relocation specifiers.
We should not report `error: invalid variant` when @ is used.

Attempt to make expr@specifier parsing less hacky.
2025-04-01 00:06:05 -07:00

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//===- MCExpr.cpp - Assembly Level Expression Implementation --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCExpr.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
using namespace llvm;
#define DEBUG_TYPE "mcexpr"
namespace {
namespace stats {
STATISTIC(MCExprEvaluate, "Number of MCExpr evaluations");
} // end namespace stats
} // end anonymous namespace
static int getPrecedence(MCBinaryExpr::Opcode Op) {
switch (Op) {
case MCBinaryExpr::Add:
case MCBinaryExpr::Sub:
return 1;
default:
return 0;
}
}
// VariantKind printing and formatting utilize MAI. operator<< (dump and some
// target code) specifies MAI as nullptr and should be avoided when MAI is
// needed.
void MCExpr::print(raw_ostream &OS, const MCAsmInfo *MAI,
int SurroundingPrec) const {
constexpr int MaxPrec = 9;
switch (getKind()) {
case MCExpr::Target:
return cast<MCTargetExpr>(this)->printImpl(OS, MAI);
case MCExpr::Constant: {
auto Value = cast<MCConstantExpr>(*this).getValue();
auto PrintInHex = cast<MCConstantExpr>(*this).useHexFormat();
auto SizeInBytes = cast<MCConstantExpr>(*this).getSizeInBytes();
if (Value < 0 && MAI && !MAI->supportsSignedData())
PrintInHex = true;
if (PrintInHex)
switch (SizeInBytes) {
default:
OS << "0x" << Twine::utohexstr(Value);
break;
case 1:
OS << format("0x%02" PRIx64, Value);
break;
case 2:
OS << format("0x%04" PRIx64, Value);
break;
case 4:
OS << format("0x%08" PRIx64, Value);
break;
case 8:
OS << format("0x%016" PRIx64, Value);
break;
}
else
OS << Value;
return;
}
case MCExpr::SymbolRef: {
const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*this);
const MCSymbol &Sym = SRE.getSymbol();
Sym.print(OS, MAI);
const MCSymbolRefExpr::VariantKind Kind = SRE.getKind();
if (Kind != MCSymbolRefExpr::VK_None) {
if (!MAI) // should only be used by dump()
OS << "@<variant " << Kind << '>';
else if (MAI->useParensForSpecifier()) // ARM
OS << '(' << MAI->getSpecifierName(Kind) << ')';
else
OS << '@' << MAI->getSpecifierName(Kind);
}
return;
}
case MCExpr::Unary: {
const MCUnaryExpr &UE = cast<MCUnaryExpr>(*this);
switch (UE.getOpcode()) {
case MCUnaryExpr::LNot: OS << '!'; break;
case MCUnaryExpr::Minus: OS << '-'; break;
case MCUnaryExpr::Not: OS << '~'; break;
case MCUnaryExpr::Plus: OS << '+'; break;
}
UE.getSubExpr()->print(OS, MAI, MaxPrec);
return;
}
case MCExpr::Binary: {
const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
// We want to avoid redundant parentheses for relocatable expressions like
// a-b+c.
//
// Print '(' if the current operator has lower precedence than the
// surrounding operator, or if the surrounding operator's precedence is
// unknown (set to HighPrecedence).
int Prec = getPrecedence(BE.getOpcode());
bool Paren = Prec < SurroundingPrec;
if (Paren)
OS << '(';
// Many operators' precedence is different from C. Set the precedence to
// HighPrecedence for unknown operators.
int SubPrec = Prec ? Prec : MaxPrec;
BE.getLHS()->print(OS, MAI, SubPrec);
switch (BE.getOpcode()) {
case MCBinaryExpr::Add:
// Print "X-42" instead of "X+-42".
if (const MCConstantExpr *RHSC = dyn_cast<MCConstantExpr>(BE.getRHS())) {
if (RHSC->getValue() < 0) {
OS << RHSC->getValue();
if (Paren)
OS << ')';
return;
}
}
OS << '+';
break;
case MCBinaryExpr::AShr: OS << ">>"; break;
case MCBinaryExpr::And: OS << '&'; break;
case MCBinaryExpr::Div: OS << '/'; break;
case MCBinaryExpr::EQ: OS << "=="; break;
case MCBinaryExpr::GT: OS << '>'; break;
case MCBinaryExpr::GTE: OS << ">="; break;
case MCBinaryExpr::LAnd: OS << "&&"; break;
case MCBinaryExpr::LOr: OS << "||"; break;
case MCBinaryExpr::LShr: OS << ">>"; break;
case MCBinaryExpr::LT: OS << '<'; break;
case MCBinaryExpr::LTE: OS << "<="; break;
case MCBinaryExpr::Mod: OS << '%'; break;
case MCBinaryExpr::Mul: OS << '*'; break;
case MCBinaryExpr::NE: OS << "!="; break;
case MCBinaryExpr::Or: OS << '|'; break;
case MCBinaryExpr::OrNot: OS << '!'; break;
case MCBinaryExpr::Shl: OS << "<<"; break;
case MCBinaryExpr::Sub: OS << '-'; break;
case MCBinaryExpr::Xor: OS << '^'; break;
}
BE.getRHS()->print(OS, MAI, SubPrec + 1);
if (Paren)
OS << ')';
return;
}
}
llvm_unreachable("Invalid expression kind!");
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void MCExpr::dump() const {
dbgs() << *this;
dbgs() << '\n';
}
#endif
bool MCExpr::isSymbolUsedInExpression(const MCSymbol *Sym) const {
switch (getKind()) {
case MCExpr::Binary: {
const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(this);
return BE->getLHS()->isSymbolUsedInExpression(Sym) ||
BE->getRHS()->isSymbolUsedInExpression(Sym);
}
case MCExpr::Target: {
const MCTargetExpr *TE = static_cast<const MCTargetExpr *>(this);
return TE->isSymbolUsedInExpression(Sym);
}
case MCExpr::Constant:
return false;
case MCExpr::SymbolRef: {
const MCSymbol &S = static_cast<const MCSymbolRefExpr *>(this)->getSymbol();
if (S.isVariable() && !S.isWeakExternal())
return S.getVariableValue()->isSymbolUsedInExpression(Sym);
return &S == Sym;
}
case MCExpr::Unary: {
const MCExpr *SubExpr =
static_cast<const MCUnaryExpr *>(this)->getSubExpr();
return SubExpr->isSymbolUsedInExpression(Sym);
}
}
llvm_unreachable("Unknown expr kind!");
}
/* *** */
const MCBinaryExpr *MCBinaryExpr::create(Opcode Opc, const MCExpr *LHS,
const MCExpr *RHS, MCContext &Ctx,
SMLoc Loc) {
return new (Ctx) MCBinaryExpr(Opc, LHS, RHS, Loc);
}
const MCUnaryExpr *MCUnaryExpr::create(Opcode Opc, const MCExpr *Expr,
MCContext &Ctx, SMLoc Loc) {
return new (Ctx) MCUnaryExpr(Opc, Expr, Loc);
}
const MCConstantExpr *MCConstantExpr::create(int64_t Value, MCContext &Ctx,
bool PrintInHex,
unsigned SizeInBytes) {
return new (Ctx) MCConstantExpr(Value, PrintInHex, SizeInBytes);
}
/* *** */
MCSymbolRefExpr::MCSymbolRefExpr(const MCSymbol *Symbol, VariantKind Kind,
const MCAsmInfo *MAI, SMLoc Loc)
: MCExpr(MCExpr::SymbolRef, Loc,
encodeSubclassData(Kind, MAI->hasSubsectionsViaSymbols())),
Symbol(Symbol) {
assert(Symbol);
}
const MCSymbolRefExpr *MCSymbolRefExpr::create(const MCSymbol *Sym,
VariantKind Kind,
MCContext &Ctx, SMLoc Loc) {
return new (Ctx) MCSymbolRefExpr(Sym, Kind, Ctx.getAsmInfo(), Loc);
}
/* *** */
void MCTargetExpr::anchor() {}
/* *** */
bool MCExpr::evaluateAsAbsolute(int64_t &Res) const {
return evaluateAsAbsolute(Res, nullptr, nullptr, false);
}
bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm,
const SectionAddrMap &Addrs) const {
// Setting InSet causes us to absolutize differences across sections and that
// is what the MachO writer uses Addrs for.
return evaluateAsAbsolute(Res, &Asm, &Addrs, true);
}
bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const {
return evaluateAsAbsolute(Res, &Asm, nullptr, false);
}
bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm) const {
return evaluateAsAbsolute(Res, Asm, nullptr, false);
}
bool MCExpr::evaluateKnownAbsolute(int64_t &Res, const MCAssembler &Asm) const {
return evaluateAsAbsolute(Res, &Asm, nullptr, true);
}
bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
const SectionAddrMap *Addrs, bool InSet) const {
MCValue Value;
// Fast path constants.
if (const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(this)) {
Res = CE->getValue();
return true;
}
bool IsRelocatable = evaluateAsRelocatableImpl(Value, Asm, Addrs, InSet);
Res = Value.getConstant();
// Value with RefKind (e.g. %hi(0xdeadbeef) in MIPS) is not considered
// absolute (the value is unknown at parse time), even if it might be resolved
// by evaluateFixup.
return IsRelocatable && Value.isAbsolute() && Value.getRefKind() == 0;
}
/// Helper method for \see EvaluateSymbolAdd().
static void AttemptToFoldSymbolOffsetDifference(
const MCAssembler *Asm, const SectionAddrMap *Addrs, bool InSet,
const MCSymbolRefExpr *&A, const MCSymbolRefExpr *&B, int64_t &Addend) {
if (!A || !B)
return;
const MCSymbol &SA = A->getSymbol();
const MCSymbol &SB = B->getSymbol();
if (SA.isUndefined() || SB.isUndefined())
return;
if (!Asm->getWriter().isSymbolRefDifferenceFullyResolved(*Asm, A, B, InSet))
return;
auto FinalizeFolding = [&]() {
// Pointers to Thumb symbols need to have their low-bit set to allow
// for interworking.
if (Asm->isThumbFunc(&SA))
Addend |= 1;
// Clear the symbol expr pointers to indicate we have folded these
// operands.
A = B = nullptr;
};
const MCFragment *FA = SA.getFragment();
const MCFragment *FB = SB.getFragment();
const MCSection &SecA = *FA->getParent();
const MCSection &SecB = *FB->getParent();
if ((&SecA != &SecB) && !Addrs)
return;
// When layout is available, we can generally compute the difference using the
// getSymbolOffset path, which also avoids the possible slow fragment walk.
// However, linker relaxation may cause incorrect fold of A-B if A and B are
// separated by a linker-relaxable instruction. If the section contains
// instructions and InSet is false (not expressions in directive like
// .size/.fill), disable the fast path.
bool Layout = Asm->hasLayout();
if (Layout && (InSet || !SecA.hasInstructions() ||
!Asm->getBackend().allowLinkerRelaxation())) {
// If both symbols are in the same fragment, return the difference of their
// offsets. canGetFragmentOffset(FA) may be false.
if (FA == FB && !SA.isVariable() && !SB.isVariable()) {
Addend += SA.getOffset() - SB.getOffset();
return FinalizeFolding();
}
// Eagerly evaluate when layout is finalized.
Addend += Asm->getSymbolOffset(A->getSymbol()) -
Asm->getSymbolOffset(B->getSymbol());
if (Addrs && (&SecA != &SecB))
Addend += (Addrs->lookup(&SecA) - Addrs->lookup(&SecB));
FinalizeFolding();
} else {
// When layout is not finalized, our ability to resolve differences between
// symbols is limited to specific cases where the fragments between two
// symbols (including the fragments the symbols are defined in) are
// fixed-size fragments so the difference can be calculated. For example,
// this is important when the Subtarget is changed and a new MCDataFragment
// is created in the case of foo: instr; .arch_extension ext; instr .if . -
// foo.
if (SA.isVariable() || SB.isVariable())
return;
// Try to find a constant displacement from FA to FB, add the displacement
// between the offset in FA of SA and the offset in FB of SB.
bool Reverse = false;
if (FA == FB)
Reverse = SA.getOffset() < SB.getOffset();
else
Reverse = FA->getLayoutOrder() < FB->getLayoutOrder();
uint64_t SAOffset = SA.getOffset(), SBOffset = SB.getOffset();
int64_t Displacement = SA.getOffset() - SB.getOffset();
if (Reverse) {
std::swap(FA, FB);
std::swap(SAOffset, SBOffset);
Displacement *= -1;
}
// Track whether B is before a relaxable instruction and whether A is after
// a relaxable instruction. If SA and SB are separated by a linker-relaxable
// instruction, the difference cannot be resolved as it may be changed by
// the linker.
bool BBeforeRelax = false, AAfterRelax = false;
for (auto FI = FB; FI; FI = FI->getNext()) {
auto DF = dyn_cast<MCDataFragment>(FI);
if (DF && DF->isLinkerRelaxable()) {
if (&*FI != FB || SBOffset != DF->getContents().size())
BBeforeRelax = true;
if (&*FI != FA || SAOffset == DF->getContents().size())
AAfterRelax = true;
if (BBeforeRelax && AAfterRelax)
return;
}
if (&*FI == FA) {
// If FA and FB belong to the same subsection, the loop will find FA and
// we can resolve the difference.
Addend += Reverse ? -Displacement : Displacement;
FinalizeFolding();
return;
}
int64_t Num;
unsigned Count;
if (DF) {
Displacement += DF->getContents().size();
} else if (auto *AF = dyn_cast<MCAlignFragment>(FI);
AF && Layout && AF->hasEmitNops() &&
!Asm->getBackend().shouldInsertExtraNopBytesForCodeAlign(
*AF, Count)) {
Displacement += Asm->computeFragmentSize(*AF);
} else if (auto *FF = dyn_cast<MCFillFragment>(FI);
FF && FF->getNumValues().evaluateAsAbsolute(Num)) {
Displacement += Num * FF->getValueSize();
} else {
return;
}
}
}
}
/// Evaluate the result of an add between (conceptually) two MCValues.
///
/// This routine conceptually attempts to construct an MCValue:
/// Result = (Result_A - Result_B + Result_Cst)
/// from two MCValue's LHS and RHS where
/// Result = LHS + RHS
/// and
/// Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
///
/// This routine attempts to aggressively fold the operands such that the result
/// is representable in an MCValue, but may not always succeed.
///
/// \returns True on success, false if the result is not representable in an
/// MCValue.
/// NOTE: It is really important to have both the Asm and Layout arguments.
/// They might look redundant, but this function can be used before layout
/// is done (see the object streamer for example) and having the Asm argument
/// lets us avoid relaxations early.
static bool evaluateSymbolicAdd(const MCAssembler *Asm,
const SectionAddrMap *Addrs, bool InSet,
const MCValue &LHS, const MCValue &RHS,
MCValue &Res) {
// FIXME: This routine (and other evaluation parts) are *incredibly* sloppy
// about dealing with modifiers. This will ultimately bite us, one day.
const MCSymbolRefExpr *LHS_A = LHS.getSymA();
const MCSymbolRefExpr *LHS_B = LHS.getSymB();
int64_t LHS_Cst = LHS.getConstant();
const MCSymbolRefExpr *RHS_A = RHS.getSymA();
const MCSymbolRefExpr *RHS_B = RHS.getSymB();
int64_t RHS_Cst = RHS.getConstant();
if (LHS.getRefKind() != RHS.getRefKind())
return false;
// Fold the result constant immediately.
int64_t Result_Cst = LHS_Cst + RHS_Cst;
// If we have a layout, we can fold resolved differences.
if (Asm) {
// First, fold out any differences which are fully resolved. By
// reassociating terms in
// Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
// we have the four possible differences:
// (LHS_A - LHS_B),
// (LHS_A - RHS_B),
// (RHS_A - LHS_B),
// (RHS_A - RHS_B).
// Since we are attempting to be as aggressive as possible about folding, we
// attempt to evaluate each possible alternative.
AttemptToFoldSymbolOffsetDifference(Asm, Addrs, InSet, LHS_A, LHS_B,
Result_Cst);
AttemptToFoldSymbolOffsetDifference(Asm, Addrs, InSet, LHS_A, RHS_B,
Result_Cst);
AttemptToFoldSymbolOffsetDifference(Asm, Addrs, InSet, RHS_A, LHS_B,
Result_Cst);
AttemptToFoldSymbolOffsetDifference(Asm, Addrs, InSet, RHS_A, RHS_B,
Result_Cst);
}
// We can't represent the addition or subtraction of two symbols.
if ((LHS_A && RHS_A) || (LHS_B && RHS_B))
return false;
// At this point, we have at most one additive symbol and one subtractive
// symbol -- find them.
const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A;
const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B;
Res = MCValue::get(A, B, Result_Cst);
return true;
}
bool MCExpr::evaluateAsRelocatable(MCValue &Res, const MCAssembler *Asm) const {
return evaluateAsRelocatableImpl(Res, Asm, nullptr, false);
}
bool MCExpr::evaluateAsValue(MCValue &Res, const MCAssembler &Asm) const {
return evaluateAsRelocatableImpl(Res, &Asm, nullptr, true);
}
static bool canExpand(const MCSymbol &Sym, bool InSet) {
if (Sym.isWeakExternal())
return false;
const MCExpr *Expr = Sym.getVariableValue();
const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
if (Inner) {
if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
return false;
}
if (InSet)
return true;
return !Sym.isInSection();
}
bool MCExpr::evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
const SectionAddrMap *Addrs,
bool InSet) const {
++stats::MCExprEvaluate;
switch (getKind()) {
case Target:
return cast<MCTargetExpr>(this)->evaluateAsRelocatableImpl(Res, Asm);
case Constant:
Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
return true;
case SymbolRef: {
const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
const MCSymbol &Sym = SRE->getSymbol();
const auto Kind = SRE->getKind();
bool Layout = Asm && Asm->hasLayout();
// Evaluate recursively if this is a variable.
if (Sym.isVariable() && (Kind == MCSymbolRefExpr::VK_None || Layout) &&
canExpand(Sym, InSet)) {
bool IsMachO = SRE->hasSubsectionsViaSymbols();
if (Sym.getVariableValue()->evaluateAsRelocatableImpl(Res, Asm, Addrs,
InSet || IsMachO)) {
if (Kind != MCSymbolRefExpr::VK_None) {
if (Res.isAbsolute()) {
Res = MCValue::get(SRE, nullptr, 0);
return true;
}
// If the reference has a variant kind, we can only handle expressions
// which evaluate exactly to a single unadorned symbol. Attach the
// original VariantKind to SymA of the result.
if (Res.getRefKind() != MCSymbolRefExpr::VK_None || !Res.getSymA() ||
Res.getSubSym() || Res.getConstant())
return false;
Res =
MCValue::get(MCSymbolRefExpr::create(&Res.getSymA()->getSymbol(),
Kind, Asm->getContext()),
Res.getSymB(), Res.getConstant(), Res.getRefKind());
}
if (!IsMachO)
return true;
const MCSymbolRefExpr *A = Res.getSymA();
auto *B = Res.getSubSym();
// FIXME: This is small hack. Given
// a = b + 4
// .long a
// the OS X assembler will completely drop the 4. We should probably
// include it in the relocation or produce an error if that is not
// possible.
// Allow constant expressions.
if (!A && !B)
return true;
// Allows aliases with zero offset.
if (Res.getConstant() == 0 && (!A || !B))
return true;
}
}
Res = MCValue::get(SRE, nullptr, 0);
return true;
}
case Unary: {
const MCUnaryExpr *AUE = cast<MCUnaryExpr>(this);
MCValue Value;
if (!AUE->getSubExpr()->evaluateAsRelocatableImpl(Value, Asm, Addrs, InSet))
return false;
switch (AUE->getOpcode()) {
case MCUnaryExpr::LNot:
if (!Value.isAbsolute())
return false;
Res = MCValue::get(!Value.getConstant());
break;
case MCUnaryExpr::Minus:
/// -(a - b + const) ==> (b - a - const)
if (Value.getSymA() && !Value.getSubSym())
return false;
// The cast avoids undefined behavior if the constant is INT64_MIN.
Res = MCValue::get(Value.getSymB(), Value.getSymA(),
-(uint64_t)Value.getConstant());
break;
case MCUnaryExpr::Not:
if (!Value.isAbsolute())
return false;
Res = MCValue::get(~Value.getConstant());
break;
case MCUnaryExpr::Plus:
Res = Value;
break;
}
return true;
}
case Binary: {
const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
MCValue LHSValue, RHSValue;
if (!ABE->getLHS()->evaluateAsRelocatableImpl(LHSValue, Asm, Addrs,
InSet) ||
!ABE->getRHS()->evaluateAsRelocatableImpl(RHSValue, Asm, Addrs,
InSet)) {
// Check if both are Target Expressions, see if we can compare them.
if (const MCTargetExpr *L = dyn_cast<MCTargetExpr>(ABE->getLHS())) {
if (const MCTargetExpr *R = dyn_cast<MCTargetExpr>(ABE->getRHS())) {
switch (ABE->getOpcode()) {
case MCBinaryExpr::EQ:
Res = MCValue::get(L->isEqualTo(R) ? -1 : 0);
return true;
case MCBinaryExpr::NE:
Res = MCValue::get(L->isEqualTo(R) ? 0 : -1);
return true;
default:
break;
}
}
}
return false;
}
// We only support a few operations on non-constant expressions, handle
// those first.
if (!LHSValue.isAbsolute() || !RHSValue.isAbsolute()) {
switch (ABE->getOpcode()) {
default:
return false;
case MCBinaryExpr::Sub:
// Negate RHS and add.
// The cast avoids undefined behavior if the constant is INT64_MIN.
return evaluateSymbolicAdd(
Asm, Addrs, InSet, LHSValue,
MCValue::get(RHSValue.getSymB(), RHSValue.getSymA(),
-(uint64_t)RHSValue.getConstant(),
RHSValue.getRefKind()),
Res);
case MCBinaryExpr::Add:
return evaluateSymbolicAdd(Asm, Addrs, InSet, LHSValue, RHSValue, Res);
}
}
// FIXME: We need target hooks for the evaluation. It may be limited in
// width, and gas defines the result of comparisons differently from
// Apple as.
int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
int64_t Result = 0;
auto Op = ABE->getOpcode();
switch (Op) {
case MCBinaryExpr::AShr: Result = LHS >> RHS; break;
case MCBinaryExpr::Add: Result = LHS + RHS; break;
case MCBinaryExpr::And: Result = LHS & RHS; break;
case MCBinaryExpr::Div:
case MCBinaryExpr::Mod:
// Handle division by zero. gas just emits a warning and keeps going,
// we try to be stricter.
// FIXME: Currently the caller of this function has no way to understand
// we're bailing out because of 'division by zero'. Therefore, it will
// emit a 'expected relocatable expression' error. It would be nice to
// change this code to emit a better diagnostic.
if (RHS == 0)
return false;
if (ABE->getOpcode() == MCBinaryExpr::Div)
Result = LHS / RHS;
else
Result = LHS % RHS;
break;
case MCBinaryExpr::EQ: Result = LHS == RHS; break;
case MCBinaryExpr::GT: Result = LHS > RHS; break;
case MCBinaryExpr::GTE: Result = LHS >= RHS; break;
case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
case MCBinaryExpr::LOr: Result = LHS || RHS; break;
case MCBinaryExpr::LShr: Result = uint64_t(LHS) >> uint64_t(RHS); break;
case MCBinaryExpr::LT: Result = LHS < RHS; break;
case MCBinaryExpr::LTE: Result = LHS <= RHS; break;
case MCBinaryExpr::Mul: Result = LHS * RHS; break;
case MCBinaryExpr::NE: Result = LHS != RHS; break;
case MCBinaryExpr::Or: Result = LHS | RHS; break;
case MCBinaryExpr::OrNot: Result = LHS | ~RHS; break;
case MCBinaryExpr::Shl: Result = uint64_t(LHS) << uint64_t(RHS); break;
case MCBinaryExpr::Sub: Result = LHS - RHS; break;
case MCBinaryExpr::Xor: Result = LHS ^ RHS; break;
}
switch (Op) {
default:
Res = MCValue::get(Result);
break;
case MCBinaryExpr::EQ:
case MCBinaryExpr::GT:
case MCBinaryExpr::GTE:
case MCBinaryExpr::LT:
case MCBinaryExpr::LTE:
case MCBinaryExpr::NE:
// A comparison operator returns a -1 if true and 0 if false.
Res = MCValue::get(Result ? -1 : 0);
break;
}
return true;
}
}
llvm_unreachable("Invalid assembly expression kind!");
}
MCFragment *MCExpr::findAssociatedFragment() const {
switch (getKind()) {
case Target:
// We never look through target specific expressions.
return cast<MCTargetExpr>(this)->findAssociatedFragment();
case Constant:
return MCSymbol::AbsolutePseudoFragment;
case SymbolRef: {
const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
const MCSymbol &Sym = SRE->getSymbol();
return Sym.getFragment();
}
case Unary:
return cast<MCUnaryExpr>(this)->getSubExpr()->findAssociatedFragment();
case Binary: {
const MCBinaryExpr *BE = cast<MCBinaryExpr>(this);
MCFragment *LHS_F = BE->getLHS()->findAssociatedFragment();
MCFragment *RHS_F = BE->getRHS()->findAssociatedFragment();
// If either is absolute, return the other.
if (LHS_F == MCSymbol::AbsolutePseudoFragment)
return RHS_F;
if (RHS_F == MCSymbol::AbsolutePseudoFragment)
return LHS_F;
// Not always correct, but probably the best we can do without more context.
if (BE->getOpcode() == MCBinaryExpr::Sub)
return MCSymbol::AbsolutePseudoFragment;
// Otherwise, return the first non-null fragment.
return LHS_F ? LHS_F : RHS_F;
}
}
llvm_unreachable("Invalid assembly expression kind!");
}
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