[RISCV] Add @earlyclobber to SiFive custom matrix multiply instruction. (#124060)

All of these have a constraint that vd and vs1 cannot overlap. Some of
them have an additional widening constraint for vs2. We should use
earlyclobber to protect this.

This is unlikely to be an issue in practice due to the instrinsic being
ternary so vd is also a source. The intrinsic has a different type for
this source than the other sources. You would have to do something crazy
to get the register allocator to overlap the registers.

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfoXSf.td

@@ -374,28 +374,28 @@ multiclass VPseudoVC_XVW<LMULInfo m, DAGOperand RS1Class,
   }
 }
 
-multiclass VPseudoSiFiveVMACC<string mx, VReg vd_type, VReg vs2_type,
-                              string Constraint = ""> {
+multiclass VPseudoSiFiveVMACC<string mx, VReg vd_type, VReg vs2_type> {
   def "Pseudo" # NAME # "_" # mx
-      : VPseudoTernaryNoMaskWithPolicy<vd_type, V_M1.vrclass, vs2_type, Constraint>;
+      : VPseudoTernaryNoMaskWithPolicy<vd_type, V_M1.vrclass, vs2_type,
+                                       "@earlyclobber $rd">;
 }
 
-multiclass VPseudoSiFiveVQMACCDOD<string Constraint = ""> {
+multiclass VPseudoSiFiveVQMACCDOD {
   foreach m = MxListVF8 in
     let VLMul = m.value in
-    defm NAME : VPseudoSiFiveVMACC<m.MX, m.vrclass, m.vrclass, Constraint>;
+    defm NAME : VPseudoSiFiveVMACC<m.MX, m.vrclass, m.vrclass>;
 }
 
-multiclass VPseudoSiFiveVQMACCQOQ<string Constraint = ""> {
+multiclass VPseudoSiFiveVQMACCQOQ {
   foreach m = [V_MF2, V_M1, V_M2, V_M4] in
     let VLMul = m.value in
-    defm NAME : VPseudoSiFiveVMACC<m.MX, m.wvrclass, m.vrclass, Constraint>;
+    defm NAME : VPseudoSiFiveVMACC<m.MX, m.wvrclass, m.vrclass>;
 }
 
-multiclass VPseudoSiFiveVFWMACC<string Constraint = ""> {
+multiclass VPseudoSiFiveVFWMACC {
   foreach m = MxListVF2 in
     let VLMul = m.value in
-    defm NAME : VPseudoSiFiveVMACC<m.MX, m.wvrclass, m.vrclass, Constraint>;
+    defm NAME : VPseudoSiFiveVMACC<m.MX, m.wvrclass, m.vrclass>;
 }
 
 multiclass VPseudoSiFiveVFNRCLIP<string Constraint = "@earlyclobber $rd"> {