[X86][AsmParser][AVX512] Error appropriately when K0 is tried as a write-mask

[coby]

Summary

K0 isn't expected as a write-mask, so provide a detailed error here, instead of the more generic one (invalid op for insn)
Conforms with gas

[m_zuckerman]

lib/Target/X86/AsmParser/X86AsmParser.cpp

2092

Why do you use a new RegLoc?

[coby]

lib/Target/X86/AsmParser/X86AsmParser.cpp

2092

To acquire the start location of the register operand, so the location mark on ther error message will be correct

[m_zuckerman]

It sounds reasonable
LGTM

lib/Target/X86/AsmParser/X86AsmParser.cpp

if (getLexer().is(AsmToken::LCurly)) {
         // Reaching here means that parsing of the allegadly '{z}' mark yielded
         // no errors.
         // Query for the need of further parsing for a {%k<NUM>} mark
         if (!Z || getLexer().is(AsmToken::LCurly)) {
           SMLoc StartLoc = Z ? consumeToken() : consumedToken;
           // Parse an op-mask register mark ({%k<NUM>}), which is now to be
           // expected
           unsigned RegNo;
-          if (!ParseRegister(RegNo, StartLoc, StartLoc) &&
+          SMLoc RegLoc;
+          if (!ParseRegister(RegNo, RegLoc, StartLoc) &&
               X86MCRegisterClasses[X86::VK1RegClassID].contains(RegNo)) {
+            if (RegNo == X86::K0)
+              return Error(RegLoc, "Register k0 can't be used as write mask");
             if (!getLexer().is(AsmToken::RCurly))
               return Error(getLexer().getLoc(), "Expected } at this point");
             Operands.push_back(X86Operand::CreateToken("{", StartLoc));
             Operands.push_back(
                 X86Operand::CreateReg(RegNo, StartLoc, StartLoc));
             Operands.push_back(X86Operand::CreateToken("}", consumeToken()));
           } else
             return Error(getLexer().getLoc(),

test/MC/X86/avx512-err.s

-// RUN: not llvm-mc -triple x86_64-unknown-unknown -mcpu=knl -mattr=+avx512dq -mattr=+avx512f --show-encoding %s 2> %t.err
-// RUN: FileCheck --check-prefix=ERR < %t.err %s
+// RUN: not llvm-mc %s -triple x86_64-unknown-unknown -mcpu=knl -mattr=+avx512dq -mattr=+avx512f --show-encoding -o /dev/null 2>&1 | FileCheck --check-prefix=ERR %s
 
-// ERR: invalid operand for instruction
+// ERR: Register k0 can't be used as write mask
 vpcmpd $1, %zmm24, %zmm7, %k5{%k0}
 
 // ERR: Expected a {z} mark at this point
 vfmsub213ps %zmm8, %zmm8, %zmm8{%k2} {rn-sae}
 
 // ERR: Expected an op-mask register at this point
 vfmsub213ps %zmm8, %zmm8, %zmm8 {rn-sae}

test/MC/X86/intel-syntax-avx512-error.s

 // RUN: not llvm-mc %s -triple x86_64-unknown-unknown -mcpu=knl -mattr=+avx512f -x86-asm-syntax=intel -output-asm-variant=1 -o /dev/null 2>&1 | FileCheck %s
 
 // Validate that only OpMask/Zero mark may immediately follow destination
   vfmsub213ps zmm8{rn-sae} {k2}, zmm8, zmm8
 // CHECK: error: Expected an op-mask register at this point
   vfmsub213ps zmm8{k2} {rn-sae}, zmm8, zmm8
 // CHECK: error: Expected a {z} mark at this point
   vfmsub213ps zmm8{rn-sae}, zmm8, zmm8
 // CHECK: error: Expected an op-mask register at this point
+  vpcmpltd k5{k0}, zmm7, zmm24
+// CHECK: error: Register k0 can't be used as write mask
+