[MC] Do not consider .ifdef/.ifndef as a use

[scott.linder]

Summary

GAS seems to allow this, and I can't think of a reason why these directives should be considered uses.

[scott.linder]

Rebase and ping

[scott.linder]

Ping

[kristina]

LGTM if GAS does allow multiple uses of .set to change the value. One nit on the test, can you add a case where you don't have an .if directive like:

.set foo, 5
# CHECK: .byte 5
.byte foo

I think it would make sense to have that at the bottom even if there is already a test for it, just to verify that plain .set semantics are still correct when preceded by several .if/.else directives.

[scott.linder]

Rebase and extend tests

[scott.linder]

Ping

[kristina]

LGTM.

lib/MC/MCParser/AsmParser.cpp

bool AsmParser::parseDirectiveIfdef(SMLoc DirectiveLoc, bool expect_defined) {
   } else {
     if (check(parseIdentifier(Name), "expected identifier after '.ifdef'") ||
         parseToken(AsmToken::EndOfStatement, "unexpected token in '.ifdef'"))
       return true;
 
     MCSymbol *Sym = getContext().lookupSymbol(Name);
 
     if (expect_defined)
-      TheCondState.CondMet = (Sym && !Sym->isUndefined());
+      TheCondState.CondMet = (Sym && !Sym->isUndefined(false));
     else
-      TheCondState.CondMet = (!Sym || Sym->isUndefined());
+      TheCondState.CondMet = (!Sym || Sym->isUndefined(false));
     TheCondState.Ignore = !TheCondState.CondMet;
   }
 
   return false;
 }
 
 /// parseDirectiveElseIf
 /// ::= .elseif expression

test/MC/AsmParser/ifdef.s

 
 # CHECK-NOT: .byte 0
 # CHECK: .byte 1
 .ifdef undefined
   .byte 0
 .else
   .byte 1
 .endif
+
+# .ifdef directive does not count as a use, so ensure redefinition is permitted
+.set var, 1
+.ifdef var
+  .set var, 2
+.else
+  .set var, 3
+.endif
+# CHECK: .byte 2
+.byte var
+
+.set var, 4
+# CHECK: .byte 4
+.byte var

test/MC/AsmParser/ifndef.s

 
 # CHECK: .byte 1
 # CHECK-NOT: byte 0
 .ifndef undefined
   .byte 1
 .else
   .byte 0
 .endif
+
+# .ifndef directive does not count as a use, so ensure redefinition is permitted
+.set var, 1
+.ifndef var
+  .set var, 2
+.else
+  .set var, 3
+.endif
+# CHECK: .byte 3
+.byte var
+
+.set var, 4
+# CHECK: .byte 4
+.byte var