[asm] Correctly handle special names in variants

[thakis]

Summary

There's really no reason why anyone should use these special names in a variant.
I noticed this while reading the code: all other writes to OS are guarded by
this conditional, and the behavior with the check seems more correct, so
let's add the check.

[hans]

I'm not familiar with this code, so apologies for the silly question, but how does this change make a difference for the new test case?

[thakis]

Without the patch, the output of the new line was bar 1 x1 since the ${:uid} in the second variant was printed despite it not being the active variant.

[hans]

Thanks! lgtm

llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp

case '$': {
       // PrintSpecial.
       if (HasCurlyBraces && *LastEmitted == ':') {
         ++LastEmitted;
         const char *StrStart = LastEmitted;
         const char *StrEnd = strchr(StrStart, '}');
         if (!StrEnd)
           report_fatal_error("Unterminated ${:foo} operand in inline asm"
                              " string: '" + Twine(AsmStr) + "'");
-
+        if (CurVariant == -1 || CurVariant == AsmPrinterVariant) {
           std::string Val(StrStart, StrEnd);
           AP->PrintSpecial(MI, OS, Val.c_str());
+        }
         LastEmitted = StrEnd+1;
         break;
       }
 
       const char *IDStart = LastEmitted;
       const char *IDEnd = IDStart;
       while (isDigit(*IDEnd))
         ++IDEnd;

llvm/test/CodeGen/Generic/inline-asm-special-strings.ll

-; RUN: llc -no-integrated-as < %s | grep "foo 0 0"
+; RUN: llc -no-integrated-as < %s | FileCheck %s
 
 define void @bar() nounwind {
-  tail call void asm sideeffect "foo ${:uid} ${:uid}", ""() nounwind
-  ret void
+  ; CHECK: foo 0 0{{$}}
+  tail call void asm sideeffect "foo ${:uid} ${:uid}", ""() nounwind
+  ; CHECK: bar 1 x{{$}}
+  tail call void asm sideeffect "bar $(${:uid} x$| ${:uid} x$)", ""() nounwind
+  ret void
 }