[X86][InlineAsm][Ms Compatibility]Prefer variable name over a register when the two collides

[coby]

Summary

On MS-style, the following snippet:

int eax;
__asm mov eax, ebx

should yield loading of ebx, into the location pointed by the variable eax

This patch sees to it.

Currently, a reg-to-reg move would have been invoked.

Test: D34740

[rnk]

I reverted this in rL308926 because it broke sanitizer-windows: http://lab.llvm.org:8011/builders/sanitizer-windows/builds/14535

With this patch, clang would reject this code:

namespace cl { }
void f() {
  __asm {
    mov al, cl
  }
}

[coby]

In D34739#819343, @rnk wrote:

I reverted this in rL308926 because it broke sanitizer-windows: http://lab.llvm.org:8011/builders/sanitizer-windows/builds/14535

With this patch, clang would reject this code:

namespace cl { }
void f() {
  __asm {
    mov al, cl
  }
}

blimey
my bad
will refine it and re-upload
thanks

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

bool X86AsmParser::ParseRegister(unsigned &RegNo,
   // without the prefix, unprefixed registers can occur in cfi directives.
   if (!isParsingIntelSyntax() && PercentTok.is(AsmToken::Percent))
     Parser.Lex(); // Eat percent token.
 
   const AsmToken &Tok = Parser.getTok();
   EndLoc = Tok.getEndLoc();
 
   if (Tok.isNot(AsmToken::Identifier)) {
-    if (isParsingIntelSyntax()) return true;
+    if (isParsingIntelSyntax())
+      return true;
     return Error(StartLoc, "invalid register name",
                  SMRange(StartLoc, EndLoc));
   }
 
   RegNo = MatchRegisterName(Tok.getString());
 
   // If the match failed, try the register name as lowercase.
   if (RegNo == 0)
     RegNo = MatchRegisterName(Tok.getString().lower());
 
+  // In MS inline-asm we allow variables to be named as registers, and
+  // give them precedence over actual registers
+  // However - we require the match to be case sensitive
+  if (isParsingInlineAsm() && isParsingIntelSyntax() && RegNo) {
+    StringRef LineBuf(Tok.getIdentifier().data());
+    InlineAsmIdentifierInfo Info;
+    if (SemaCallback->LookupInlineAsmIdentifier(LineBuf, Info, false))
+      return true;
+  }
+
   // 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