[Sparc] Accept %0 through %31 as registers in assembly code.

[dougk]

Summary

This syntax appears in actual code in the wild, and is valid according to gnu as.

[jyknight]

I'm not sure this is actually a good idea. The asm file in question seems
to me probably to have just been a typo. (Says %0 in one place, instead of
%g0 or 0.)

Unless there's more widespread usage of this, I think it might be better to
treat that "%0" usage as a bug, and just fix it, rather than adding support
for this confusing register-naming variant in llvm.

Solaris 'as' also doesn't accept that syntax.
$ echo "mov %0, %g1" > /tmp/test.s
$ as -o /tmp/test.o /tmp/test.s
as: "/tmp/test.s", line 1: error: statement syntax

lib/Target/Sparc/AsmParser/SparcAsmParser.cpp

       return true;
     }
   }
+  // For compatibility with other assemblers, %0 through %31 refer to integer
+  // registers without subdividing them into globals,locals,outs,ins.
+  // Strictly speaking, the valid spellings exclude alternative ways of
+  // writing the decimal integers, but the lexer doesn't know that.
+  if (Tok.is(AsmToken::Integer)) {
+    intVal = Tok.getIntVal();
+    // The size() check rejects "%001", "%0b1", "%0x1" as putative spellings.
+    if (intVal >= 0 && intVal < 32 && Tok.getString().size()<= 2) {
+        RegNo = IntRegs[intVal];
+        RegKind = SparcOperand::rk_IntReg;
+        return true;
+    }
+  }
   return false;
 }
 

test/MC/Sparc/sparc-alu-instructions.s

 
         ! CHECK:  tsubcctv %g2, %g1, %g3          ! encoding: [0x87,0x18,0x80,0x01]
         tsubcctv %g2, %g1, %g3
+
+        ! "%0" is a synonym for "%g0" and so on
+        ! CHECK:   mov   %g0, %i7                 ! encoding: [0xbe,0x10,0x00,0x00]
+        mov %0, %31