[RISCV] Add FallbackRegAltNameIndex to ABIRegAltName.

Remove now redundant fake ABI names from vector registers.

This also fixes a crash that occurs if you use fflags as an instruction
operand in the assembly and use -debug. It's not a valid register
for any instruction since this wouldn't be common. It doesn't have
an ABI name so it crashes the register printing in the debug output.

Author: topperc

llvm/lib/Target/RISCV/RISCVRegisterInfo.td

@@ -45,6 +45,7 @@ class RISCVReg64<RISCVReg32 subreg>
   let SubRegIndices = [sub_32];
 }
 
+let FallbackRegAltNameIndex = NoRegAltName in
 def ABIRegAltName : RegAltNameIndex;
 
 def sub_vrm4_0 : SubRegIndex<256>;
@@ -415,51 +416,46 @@ class VRegList<list<dag> LIn, int start, int nf, int lmul, bit isV0> {
 }
 
 // Vector registers
-let RegAltNameIndices = [ABIRegAltName] in {
-  foreach Index = 0-31 in {
-    def V#Index : RISCVReg<Index, "v"#Index, ["v"#Index]>, DwarfRegNum<[!add(Index, 96)]>;
-  }
+foreach Index = 0-31 in {
+  def V#Index : RISCVReg<Index, "v"#Index>, DwarfRegNum<[!add(Index, 96)]>;
+}
 
-  foreach Index = [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22,
-                   24, 26, 28, 30] in {
-    def V#Index#M2 : RISCVRegWithSubRegs<Index, "v"#Index,
-                       [!cast<Register>("V"#Index),
-                        !cast<Register>("V"#!add(Index, 1))],
-                       ["v"#Index]>,
-                     DwarfRegAlias<!cast<Register>("V"#Index)> {
-      let SubRegIndices = [sub_vrm1_0, sub_vrm1_1];
-    }
+foreach Index = [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22,
+                 24, 26, 28, 30] in {
+  def V#Index#M2 : RISCVRegWithSubRegs<Index, "v"#Index,
+                     [!cast<Register>("V"#Index),
+                      !cast<Register>("V"#!add(Index, 1))]>,
+                   DwarfRegAlias<!cast<Register>("V"#Index)> {
+    let SubRegIndices = [sub_vrm1_0, sub_vrm1_1];
   }
+}
 
-  foreach Index = [0, 4, 8, 12, 16, 20, 24, 28] in {
-    def V#Index#M4 : RISCVRegWithSubRegs<Index, "v"#Index,
-                       [!cast<Register>("V"#Index#"M2"),
-                        !cast<Register>("V"#!add(Index, 2)#"M2")],
-                       ["v"#Index]>,
-                     DwarfRegAlias<!cast<Register>("V"#Index)> {
-      let SubRegIndices = [sub_vrm2_0, sub_vrm2_1];
-    }
+foreach Index = [0, 4, 8, 12, 16, 20, 24, 28] in {
+  def V#Index#M4 : RISCVRegWithSubRegs<Index, "v"#Index,
+                     [!cast<Register>("V"#Index#"M2"),
+                      !cast<Register>("V"#!add(Index, 2)#"M2")]>,
+                   DwarfRegAlias<!cast<Register>("V"#Index)> {
+    let SubRegIndices = [sub_vrm2_0, sub_vrm2_1];
   }
+}
 
-  foreach Index = [0, 8, 16, 24] in {
-    def V#Index#M8 : RISCVRegWithSubRegs<Index, "v"#Index,
-                       [!cast<Register>("V"#Index#"M4"),
-                        !cast<Register>("V"#!add(Index, 4)#"M4")],
-                       ["v"#Index]>,
-                     DwarfRegAlias<!cast<Register>("V"#Index)> {
-      let SubRegIndices = [sub_vrm4_0, sub_vrm4_1];
-    }
+foreach Index = [0, 8, 16, 24] in {
+  def V#Index#M8 : RISCVRegWithSubRegs<Index, "v"#Index,
+                     [!cast<Register>("V"#Index#"M4"),
+                      !cast<Register>("V"#!add(Index, 4)#"M4")]>,
+                   DwarfRegAlias<!cast<Register>("V"#Index)> {
+    let SubRegIndices = [sub_vrm4_0, sub_vrm4_1];
   }
-
-  def VTYPE  : RISCVReg<0, "vtype", ["vtype"]>;
-  def VL     : RISCVReg<0, "vl", ["vl"]>;
-  def VXSAT  : RISCVReg<0, "vxsat", ["vxsat"]>;
-  def VXRM   : RISCVReg<0, "vxrm", ["vxrm"]>;
-  let isConstant = true in
-  def VLENB  : RISCVReg<0, "vlenb", ["vlenb"]>,
-               DwarfRegNum<[!add(4096, SysRegVLENB.Encoding)]>;
 }
 
+def VTYPE  : RISCVReg<0, "vtype">;
+def VL     : RISCVReg<0, "vl">;
+def VXSAT  : RISCVReg<0, "vxsat">;
+def VXRM   : RISCVReg<0, "vxrm">;
+let isConstant = true in
+def VLENB  : RISCVReg<0, "vlenb">,
+             DwarfRegNum<[!add(4096, SysRegVLENB.Encoding)]>;
+
 def VCSR : RegisterClass<"RISCV", [XLenVT], 32,
                           (add VTYPE, VL, VLENB)> {
   let RegInfos = XLenRI;