MIPS: Support '%w' token in inline asm template for MSA (llvm#91920)

MSA registers share the FPRs as its bottom half. So that we can use MSA
instructions to work with normal float/double:
   double a, b, c;
   asm volatile ("fmadd.d %w0, %w1, %w2" : "+f"(a) : "f"(b), "f"(c));

GCC has support it for quite long time.

Author: wzssyqa

llvm/lib/Target/Mips/MCTargetDesc/MipsBaseInfo.h

@@ -135,6 +135,15 @@ namespace MipsII {
     OPERAND_LAST_MIPS_MEM_IMM = OPERAND_MEM_SIMM9
   };
 }
+
+inline static MCRegister getMSARegFromFReg(MCRegister Reg) {
+  if (Reg >= Mips::F0 && Reg <= Mips::F31)
+    return Reg - Mips::F0 + Mips::W0;
+  else if (Reg >= Mips::D0_64 && Reg <= Mips::D31_64)
+    return Reg - Mips::D0_64 + Mips::W0;
+  else
+    return Mips::NoRegister;
+}
 }
 
 #endif

llvm/lib/Target/Mips/MipsAsmPrinter.cpp

@@ -565,12 +565,15 @@ bool MipsAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
       }
       break;
     }
-    case 'w':
-      // Print MSA registers for the 'f' constraint
-      // In LLVM, the 'w' modifier doesn't need to do anything.
-      // We can just call printOperand as normal.
+    case 'w': {
+      MCRegister w = getMSARegFromFReg(MO.getReg());
+      if (w != Mips::NoRegister) {
+        O << '$' << MipsInstPrinter::getRegisterName(w);
+        return false;
+      }
       break;
     }
+    }
   }
 
   printOperand(MI, OpNum, O);

llvm/test/CodeGen/Mips/msa/inline-asm.ll

@@ -32,3 +32,19 @@ entry:
   store <4 x i32> %1, ptr @v4i32_r
   ret void
 }
+
+define dso_local double @test4(double noundef %a, double noundef %b, double noundef %c) {
+entry:
+  ; CHECK-LABEL: test4:
+  %0 = tail call double asm sideeffect "fmadd.d ${0:w}, ${1:w}, ${2:w}", "=f,f,f,0,~{$1}"(double %b, double %c, double %a)
+  ; CHECK: fmadd.d $w{{([0-9]|[1-3][0-9])}}, $w{{([0-9]|[1-3][0-9])}}, $w{{([0-9]|[1-3][0-9])}}
+  ret double %0
+}
+
+define dso_local float @test5(float noundef %a, float noundef %b, float noundef %c) {
+entry:
+  ; CHECK-LABEL: test5:
+  %0 = tail call float asm sideeffect "fmadd.w ${0:w}, ${1:w}, ${2:w}", "=f,f,f,0,~{$1}"(float %b, float %c, float %a)
+  ; CHECK: fmadd.w $w{{([0-9]|[1-3][0-9])}}, $w{{([0-9]|[1-3][0-9])}}, $w{{([0-9]|[1-3][0-9])}}
+  ret float %0
+}