[x86][ms-inline-asm] use of "jmp short" in asm is not supported

[• zizhar]

Summary

The following patch is for compatability with Microsoft.
Microsoft ignores the keyword "short" when used after a jmp, for example:

__asm {
    jmp short label
  label:
}

Currently llvm fails on this code.
In order to be Microsoft compatible, we should allow the previous example.

A test for that patch will be added in another ticket, since it's located in clang's codegen tests. Link will be added shortly.

Edit: link to test: https://reviews.llvm.org/D24958

[rnk]

lgtm

lib/Target/X86/AsmParser/X86AsmParser.cpp

2142

I wish we had an explicit "short jump" assembly instruction, though. :( Anyway, for now we should do this for compatibility.

[rnk]

Actually, there are some minor style issues, but otherwise this is OK.

lib/Target/X86/AsmParser/X86AsmParser.cpp

2136

Follow the LLVM naming convention, "NextTok"

2139

format

2145

formatting

[• zizhar]

fixed :>

[rnk]

lgtm, sorry for the delay, vacation strikes

lib/Target/X86/AsmParser/X86AsmParser.cpp

   InstInfo = &Info;
   StringRef PatchedName = Name;
 
+  if (Name == "jmp" && isParsingIntelSyntax() && isParsingInlineAsm()) {
+    StringRef NextTok = Parser.getTok().getString();
+    if (NextTok == "short") {
+      SMLoc NameEndLoc =
+          NameLoc.getFromPointer(NameLoc.getPointer() + Name.size());
+      // Eat the short keyword
+      Parser.Lex();
+      // MS ignores the short keyword, it determines the jmp type based
+      // on the distance of the label
+      InstInfo->AsmRewrites->emplace_back(AOK_Skip, NameEndLoc,
+                                          NextTok.size() + 1);
+    }
+  }
+
   // FIXME: Hack to recognize setneb as setne.
   if (PatchedName.startswith("set") && PatchedName.endswith("b") &&
       PatchedName != "setb" && PatchedName != "setnb")