[mips] [IAS] Allow .set assignments for already defined symbols.

[tomatabacu]

Summary

This is not possible when using the IAS for MIPS, but it is possible when using the IAS for other architectures and when using GAS for MIPS.

[dsanders]

Please add a test to check that something like:

  .set foo, a
  .set foo, b
a:
  nop
b:

results in foo being an alias for b.

With that test added it will LGTM.

[tomatabacu]

Added the requested test case.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

bool MipsAsmParser::parseSetAssignment() {
 
   if (getLexer().isNot(AsmToken::Comma))
     return reportParseError("unexpected token, expected comma");
   Lex(); // Eat comma
 
   if (Parser.parseExpression(Value))
     return reportParseError("expected valid expression after comma");
 
-  // Check if the Name already exists as a symbol.
-  MCSymbol *Sym = getContext().LookupSymbol(Name);
-  if (Sym)
-    return reportParseError("symbol already defined");
-  Sym = getContext().GetOrCreateSymbol(Name);
+  MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
   Sym->setVariableValue(Value);
 
   return false;
 }
 
 bool MipsAsmParser::parseSetMips0Directive() {
   MCAsmParser &Parser = getParser();
   Parser.Lex();

test/MC/Mips/set-defined-symbol.s

+# RUN: llvm-mc %s -arch=mips -mcpu=mips32 -filetype=obj -o - | \
+# RUN:   llvm-objdump -d -r -arch=mips - | FileCheck %s
+
+  .global foo
+  .weak bar
+  .set bar, b
+  .set foo, b
+  .set foo, a
+a:
+  nop
+# CHECK-NOT: a:
+# CHECK: foo:
+
+b:
+  nop
+# CHECK-NOT: b:
+# CHECK-NOT: foo:
+# CHECK: bar: