[mips] Allow $AT to be used as a register name

[stanislav.ocovaj]

Summary

This patch allows $AT to be used as a register name in assembly files. Currently only $at is recognized as a valid register name.

[sdardis]

Nit inlined.

Also you should extend test/MC/Mips/mips64-register-names-{n32-n64,o32}.s .

LGTM with those nits addressed.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

5109–5110

.Cases("at", "AT", 1) instead.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

getSourceManager().PrintMessage(Range.Start, SourceMgr::DK_Warning, Msg,
                                   ShowColors);
 }
 
 int MipsAsmParser::matchCPURegisterName(StringRef Name) {
   int CC;
 
   CC = StringSwitch<unsigned>(Name)
            .Case("zero", 0)
-           .Case("at", 1)
+           .Cases("at", "AT", 1)
            .Case("a0", 4)
            .Case("a1", 5)
            .Case("a2", 6)
            .Case("a3", 7)
            .Case("v0", 2)
            .Case("v1", 3)
            .Case("s0", 16)
            .Case("s1", 17)
            .Case("s2", 18)

test/MC/Mips/mips-register-names-o32.s

 # RUN: llvm-mc %s -triple=mips-unknown-freebsd -show-encoding | FileCheck %s
 
 # Check that the register names are mapped to their correct numbers for o32
 # Second byte of addiu with $zero at rt contains the number of the source
 # register.
 
 .set noat
 addiu $zero, $zero, 0 # CHECK: encoding: [0x24,0x00,0x00,0x00]
 addiu $at, $zero, 0   # CHECK: encoding: [0x24,0x01,0x00,0x00]
+addiu $AT, $zero, 0   # CHECK: encoding: [0x24,0x01,0x00,0x00]
 addiu $v0, $zero, 0   # CHECK: encoding: [0x24,0x02,0x00,0x00]
 addiu $v1, $zero, 0   # CHECK: encoding: [0x24,0x03,0x00,0x00]
 addiu $a0, $zero, 0   # CHECK: encoding: [0x24,0x04,0x00,0x00]
 addiu $a1, $zero, 0   # CHECK: encoding: [0x24,0x05,0x00,0x00]
 addiu $a2, $zero, 0   # CHECK: encoding: [0x24,0x06,0x00,0x00]
 addiu $a3, $zero, 0   # CHECK: encoding: [0x24,0x07,0x00,0x00]
 addiu $t0, $zero, 0   # CHECK: encoding: [0x24,0x08,0x00,0x00]
 addiu $t1, $zero, 0   # CHECK: encoding: [0x24,0x09,0x00,0x00]

test/MC/Mips/mips64-register-names-o32.s

 # RUN: llvm-mc %s -triple=mips64-unknown-freebsd -show-encoding \
 # RUN:     -target-abi o32 | FileCheck %s
 
 # Check that the register names are mapped to their correct numbers for o32
 # Second byte of addiu with $zero at rt contains the number of the source
 # register.
 
 .set noat
 addiu $zero, $zero, 0 # CHECK: encoding: [0x24,0x00,0x00,0x00]
 addiu $at, $zero, 0   # CHECK: encoding: [0x24,0x01,0x00,0x00]
+addiu $AT, $zero, 0   # CHECK: encoding: [0x24,0x01,0x00,0x00]
 addiu $v0, $zero, 0   # CHECK: encoding: [0x24,0x02,0x00,0x00]
 addiu $v1, $zero, 0   # CHECK: encoding: [0x24,0x03,0x00,0x00]
 addiu $a0, $zero, 0   # CHECK: encoding: [0x24,0x04,0x00,0x00]
 addiu $a1, $zero, 0   # CHECK: encoding: [0x24,0x05,0x00,0x00]
 addiu $a2, $zero, 0   # CHECK: encoding: [0x24,0x06,0x00,0x00]
 addiu $a3, $zero, 0   # CHECK: encoding: [0x24,0x07,0x00,0x00]
 addiu $t0, $zero, 0   # CHECK: encoding: [0x24,0x08,0x00,0x00]
 addiu $t1, $zero, 0   # CHECK: encoding: [0x24,0x09,0x00,0x00]