[Mips] Add 'j' alias for r6 (llvm#196706)

Fix llvm#107460.

Author: yingopq

llvm/lib/Target/Mips/MipsInstrInfo.td

@@ -2727,7 +2727,9 @@ let AdditionalPredicates = [NotInMicroMips] in {
   def : MipsInstAlias<"bal $offset", (BGEZAL ZERO, brtarget:$offset), 1>,
         ISA_MIPS1_NOT_32R6_64R6;
 
-  def : MipsInstAlias<"j $rs", (JR GPR32Opnd:$rs), 0>, ISA_MIPS1;
+  def : MipsInstAlias<"j $rs", (JR GPR32Opnd:$rs), 0>, ISA_MIPS1_NOT_32R6_64R6;
+
+  def : MipsInstAlias<"j $rs", (JALR RA, GPR32Opnd:$rs), 0>, ISA_MIPS32R6;
 
   def : MipsInstAlias<"jalr $rs", (JALR RA, GPR32Opnd:$rs), 0>;
 

llvm/test/MC/Mips/j-alias-r6.s

@@ -0,0 +1,10 @@
+# RUN: llvm-mc -triple=mips-unknown-linux -show-inst -mcpu=mips32r5 %s \
+# RUN:   | FileCheck --check-prefix=R5 %s
+# RUN: llvm-mc -triple=mips-unknown-linux -show-inst -mcpu=mips32r6 %s \
+# RUN:   | FileCheck --check-prefix=R6 %s
+
+  .text
+  j $ra
+
+# R5:    jr $ra
+# R6:    jalr $ra