[VE] Support register aliases in llvm-mc

[kaz7]

Summary

Support register aliases in MC layer to compile existing assembly
files with clang and integrated assembler.

llvm/lib/Target/VE/VERegisterInfo.td

 // Generic floating point registers - 32 bits wide
 //   NOTE: Mark SF#I as alias of SW#I temporary to avoid register allocation
 //         problem.
 foreach I = 0-63 in
   def SF#I : VEReg<I, "sf"#I, [], ["s"#I], [!cast<VEReg>("SW"#I)]>,
                    DwarfRegNum<[I]>;
 
 // Generic integer registers - 64 bits wide
-let SubRegIndices = [sub_i32, sub_f32], CoveredBySubRegs = 1 in
-foreach I = 0-63 in
+let SubRegIndices = [sub_i32, sub_f32], CoveredBySubRegs = 1 in {
+  // Several registers have specific names, so add them to one of aliases.
+  def SX8 : VEReg<8, "s8", [SW8, SF8], ["s8", "sl"]>, DwarfRegNum<[8]>;
+  def SX9 : VEReg<9, "s9", [SW9, SF9], ["s9", "fp"]>, DwarfRegNum<[9]>;
+  def SX10 : VEReg<10, "s10", [SW10, SF10], ["s10", "lr"]>, DwarfRegNum<[10]>;
+  def SX11 : VEReg<11, "s11", [SW11, SF11], ["s11", "sp"]>, DwarfRegNum<[11]>;
+  def SX14 : VEReg<14, "s14", [SW14, SF14], ["s14", "tp"]>, DwarfRegNum<[14]>;
+  def SX15 : VEReg<15, "s15", [SW15, SF15], ["s15", "got"]>, DwarfRegNum<[15]>;
+  def SX16 : VEReg<16, "s16", [SW16, SF16], ["s16", "plt"]>, DwarfRegNum<[16]>;
+
+  // Other generic registers.
+  foreach I = { 0-7, 12-13, 17-63 } in
     def SX#I : VEReg<I, "s"#I, [!cast<VEReg>("SW"#I), !cast<VEReg>("SF"#I)],
                      ["s"#I]>, DwarfRegNum<[I]>;
+}
 
 // Aliases of the S* registers used to hold 128-bit for values (long doubles).
 // Following foreach represents something like:
 //   def Q0 : VEReg<0, "q0", [SX0, SX1], ["s0"]>;
 //   def Q1 : VEReg<2, "q2", [SX2, SX3], ["s2"]>;
 //   ...
 let SubRegIndices = [sub_even, sub_odd], CoveredBySubRegs = 1 in
 foreach I = 0-31 in

llvm/test/MC/VE/register.s

+# RUN: llvm-mc -triple=ve %s -o - | FileCheck %s
+# RUN: llvm-mc -triple=ve -filetype=obj < %s | llvm-objdump -d - \
+# RUN:     | FileCheck %s --check-prefixes=CHECK-INST
+
+### Test registers with specific names like "%sp"
+
+        subu.l %fp, %sp, %s0
+        brge.l.t %sp, %sl, 1f
+        ld %s63, 0x18(,%tp)
+1:
+        or %got, 0, %plt
+        b.l (,%lr)
+
+
+# CHECK:        subu.l %s9, %s11, %s0
+# CHECK-NEXT:   brge.l.t %s11, %s8, .Ltmp0
+# CHECK-NEXT:   ld %s63, 24(, %s14)
+# CHECK-NEXT: .Ltmp0:
+# CHECK-NEXT:   or %s15, 0, %s16
+# CHECK-NEXT:   b.l (, %s10)
+
+# CHECK-INST:        subu.l %s9, %s11, %s0
+# CHECK-INST-NEXT:   brge.l.t %s11, %s8, 16
+# CHECK-INST-NEXT:   ld %s63, 24(, %s14)
+# CHECK-INST-NEXT:   or %s15, 0, %s16
+# CHECK-INST-NEXT:   b.l (, %s10)