Fix conflict for referencing "flags" variable in X86 assembly syntax

[myatsina]

Summary

This asm instruction passes compilation:
mov eax, flags2

This asm instruction fails compilation:
mov eax, flags

When parsing the latter, the X86AsmParser “flags” should be matched to a memory location and not to the implicit EFLAGS register.

Test case uploaded in review:
http://reviews.llvm.org/D11513

[myatsina]

Test case is in the following review:

http://reviews.llvm.org/D11513

[rnk]

lib/Target/X86/AsmParser/X86AsmParser.cpp

808 ↗

(On Diff #30656)

I don't think you need the helper method in this case. I expect there will only ever be one caller, so you can just inline it.

922 ↗

(On Diff #30656)

I'm thinking:

// The "flags" register cannot be referenced directly. Treat it as an identifier instead.
if (isParsingInlineAsm() && RegNo == X86::EFLAGS)
  RegNo = 0;

[myatsina]

I've added "isParsingIntelSyntax" because we should not encounter this issue in att syntax (for att memory location has a $ sign - $flags)

lib/Target/X86/AsmParser/X86AsmParser.cpp

915 ↗

(On Diff #30825)

I've added "isParsingIntelSyntax" because we should not encounter this issue in att syntax (for att memory location has a $ sign - $flags)

[rnk]

lgtm

llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp

bool X86AsmParser::ParseRegister(unsigned &RegNo,
   }
 
   RegNo = MatchRegisterName(Tok.getString());
 
   // If the match failed, try the register name as lowercase.
   if (RegNo == 0)
     RegNo = MatchRegisterName(Tok.getString().lower());
 
+  // The "flags" register cannot be referenced directly.
+  // Treat it as an identifier instead.
+  if (isParsingInlineAsm() && isParsingIntelSyntax() && RegNo == X86::EFLAGS)
+    RegNo = 0;
+
   if (!is64BitMode()) {
     // FIXME: This should be done using Requires<Not64BitMode> and
     // Requires<In64BitMode> so "eiz" usage in 64-bit instructions can be also
     // checked.
     // FIXME: Check AH, CH, DH, BH cannot be used in an instruction requiring a
     // REX prefix.
     if (RegNo == X86::RIZ ||
         X86MCRegisterClasses[X86::GR64RegClassID].contains(RegNo) ||