[mips] Tolerate the use of the %z inline asm operand modifier with no…

…n-immediates.

Summary:
Currently, we give an error if %z is used with non-immediates, instead of continuing as if the %z isn't there.

For example, you use the %z operand modifier along with the "Jr" constraints ("r" makes the operand a register, and "J" makes it an immediate, but only if its value is 0). 
In this case, you want the compiler to print "$0" if the inline asm input operand turns out to be an immediate zero and you want it to print the register containing the operand, if it's not.

We give an error in the latter case, and we shouldn't (GCC also doesn't).

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D6023

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221453 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MipsAsmPrinter.cpp

@@ -473,14 +473,12 @@ bool MipsAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
       return false;
     case 'z': {
       // $0 if zero, regular printing otherwise
-      if (MO.getType() != MachineOperand::MO_Immediate)
-        return true;
-      int64_t Val = MO.getImm();
-      if (Val)
-        O << Val;
-      else
+      if (MO.getType() == MachineOperand::MO_Immediate && MO.getImm() == 0) {
         O << "$0";
-      return false;
+        return false;
+      }
+      // If not, call printOperand as normal.
+      break;
     }
     case 'D': // Second part of a double word register operand
     case 'L': // Low order register of a double word register operand

test/CodeGen/Mips/inlineasm-operand-code.ll

@@ -65,6 +65,33 @@ entry:
 ;CHECK_LITTLE_32:    addiu ${{[0-9]+}},${{[0-9]+}},$0
 ;CHECK_LITTLE_32:    #NO_APP
   tail call i32 asm sideeffect "addiu $0,$1,${2:z}", "=r,r,I"(i32 7, i32 0) nounwind
+
+; z with non-zero and the "r"(register) and "J"(integer zero) constraints
+;CHECK_LITTLE_32:    #APP
+;CHECK_LITTLE_32:    mtc0 ${{[1-9][0-9]?}}, ${{[0-9]+}}
+;CHECK_LITTLE_32:    #NO_APP
+  call void asm sideeffect "mtc0 ${0:z}, $$12", "Jr"(i32 7) nounwind
+
+; z with zero and the "r"(register) and "J"(integer zero) constraints
+;CHECK_LITTLE_32:    #APP
+;CHECK_LITTLE_32:    mtc0 $0, ${{[0-9]+}}
+;CHECK_LITTLE_32:    #NO_APP
+  call void asm sideeffect "mtc0 ${0:z}, $$12", "Jr"(i32 0) nounwind
+
+; z with non-zero and just the "r"(register) constraint
+;CHECK_LITTLE_32:    #APP
+;CHECK_LITTLE_32:    mtc0 ${{[1-9][0-9]?}}, ${{[0-9]+}}
+;CHECK_LITTLE_32:    #NO_APP
+  call void asm sideeffect "mtc0 ${0:z}, $$12", "r"(i32 7) nounwind
+
+; z with zero and just the "r"(register) constraint
+; FIXME: Check for $0, instead of other registers.
+;        We should be using $0 directly in this case, not real registers.
+;        When the materialization of 0 gets fixed, this test will fail.
+;CHECK_LITTLE_32:    #APP
+;CHECK_LITTLE_32:    mtc0 ${{[1-9][0-9]?}}, ${{[0-9]+}}
+;CHECK_LITTLE_32:    #NO_APP
+  call void asm sideeffect "mtc0 ${0:z}, $$12", "r"(i32 0) nounwind
   ret i32 0
 }