[X86][Asm] Allow negative immediate to appear before bracketed expression

[coby]

Summary

Currently, only non-negative immediate is allowed prior to a brac expression (memory reference).
MASM / GAS does not have any problem cope with the left side of the real line, so we should be able to as well.

Test: D36230

[rnk]

lgtm, huh, no idea why that was there...

[efriedma]

Needs testcase.

lib/Target/X86/AsmParser/X86AsmParser.cpp

1943

It looks like this is implicitly truncating Imm from int64_t to int?

[efriedma]

Oh, didn't spot the reference to D36230 for the testcase. It would still be nice to add a testcase to the LLVM repo, though (using "llvm-mc -x86-asm-syntax=intel").

[coby]

lib/Target/X86/AsmParser/X86AsmParser.cpp

1943

Indeed. thx :)

[coby]

commited as rL310528

include/llvm/MC/MCParser/MCTargetAsmParser.h

const char AsmRewritePrecedence [] = {
   5, // AOK_EndOfStatement
   2  // AOK_Skip
 };
 
 struct AsmRewrite {
   AsmRewriteKind Kind;
   SMLoc Loc;
   unsigned Len;
-  unsigned Val;
+  int Val;
   StringRef Label;
 
 public:
-  AsmRewrite(AsmRewriteKind kind, SMLoc loc, unsigned len = 0, unsigned val = 0)
+  AsmRewrite(AsmRewriteKind kind, SMLoc loc, unsigned len = 0, int val = 0)
     : Kind(kind), Loc(loc), Len(len), Val(val) {}
   AsmRewrite(AsmRewriteKind kind, SMLoc loc, unsigned len, StringRef label)
     : Kind(kind), Loc(loc), Len(len), Val(0), Label(label) {}
 };
 
 struct ParseInstructionInfo {
   SmallVectorImpl<AsmRewrite> *AsmRewrites = nullptr;
 

lib/Target/X86/AsmParser/X86AsmParser.cpp

std::unique_ptr<X86Operand> X86AsmParser::ParseIntelOperand() {
   if (StartTok.isNot(AsmToken::Identifier) &&
       StartTok.isNot(AsmToken::String) && isParsingInlineAsm()) {
     unsigned Len = Tok.getLoc().getPointer() - Start.getPointer();
     if (StartTok.getString().size() == Len)
       // Just add a prefix if this wasn't a complex immediate expression.
       InstInfo->AsmRewrites->emplace_back(AOK_ImmPrefix, Start);
     else
       // Otherwise, rewrite the complex expression as a single immediate.
       InstInfo->AsmRewrites->emplace_back(AOK_Imm, Start, Len, Imm);
   }
 
   if (getLexer().isNot(AsmToken::LBrac)) {
     // If a directional label (ie. 1f or 2b) was parsed above from
     // ParseIntelExpression() then SM.getSym() was set to a pointer to
     // to the MCExpr with the directional local symbol and this is a
     // memory operand not an immediate operand.
     if (isSymbol) {
       if (isParsingInlineAsm())
         return CreateMemForInlineAsm(/*SegReg=*/0, SM.getSym(), /*BaseReg=*/0,
                                      /*IndexReg=*/0,
                                      /*Scale=*/1, Start, End, Size,
                                      SM.getSymName(), SM.getIdentifierInfo());
       return X86Operand::CreateMem(getPointerWidth(), SM.getSym(), Start, End,
                                    Size);
     }
 
     const MCExpr *ImmExpr = MCConstantExpr::create(Imm, getContext());
     return X86Operand::CreateImm(ImmExpr, Start, End);
   }
 
-  // Only positive immediates are valid.
-  if (Imm < 0)
-    return ErrorOperand(Start, "expected a positive immediate displacement "
-                               "before bracketed expr.");
-
   return ParseIntelBracExpression(/*SegReg=*/0, Start, Imm, isSymbol, Size);
 }
 
 std::unique_ptr<X86Operand> X86AsmParser::ParseATTOperand() {
   MCAsmParser &Parser = getParser();
   switch (getLexer().getKind()) {
   default:
     // Parse a memory operand with no segment register.