[RISCV] Don't persist invalid feature state on .option arch error

[jrtc27]

Summary

Otherwise subsequent .option arch, +foo directives (but not -, since
those have their own separate validation) fail the parseFeatureBits
check, leading to cascading errors.

[luismarques]

LGTM.

[MaskRay]

llvm/test/MC/RISCV/option-invalid.s

50

[jrtc27]

Use --implicit-check-not for a more general approach

[jrtc27]

llvm/test/MC/RISCV/option-invalid.s

50

Short comments don't normally get full stops?

[MaskRay]

llvm/test/MC/RISCV/option-invalid.s

50

In comments, a complete sentence gets a full stop. An incomplete one doesn't.
There may be cases where a short complete sentence doesn't get a full stop, but I think we don't encourage that:)

(
As a difference, diagnostic messages typically do not get full stops
https://llvm.org/docs/CodingStandards.html#error-and-warning-messages
)

[jrtc27]

llvm/test/MC/RISCV/option-invalid.s

50

Like many comments I view this more as a sentence fragment that happens to technically be a complete sentence. Adding a full stop changes the tone of the comment in a way that isn't appropriate IMO. I'm not fundamentally opposed to it, it just feels quite unnatural to do.

[MaskRay]

llvm/test/MC/RISCV/option-invalid.s

50

OK, I don't actually mind much about the comment style in the tests. It was just a suggestion. Feel free to land the patch as is:)

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

 //===-- RISCVAsmParser.cpp - Parse RISC-V assembly to MCInst instructions -===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
do {
               Loc,
               "Extension version number parsing not currently implemented");
         return Error(Loc, "unknown extension feature");
       }
 
       Args.emplace_back(Type, Ext->Key);
 
       if (Type == RISCVOptionArchArgType::Plus) {
+        FeatureBitset OldFeatureBits = STI->getFeatureBits();
+
         setFeatureBits(Ext->Value, Ext->Key);
         auto ParseResult = RISCVFeatures::parseFeatureBits(isRV64(), STI->getFeatureBits());
         if (!ParseResult) {
+          copySTI().setFeatureBits(OldFeatureBits);
+          setAvailableFeatures(ComputeAvailableFeatures(OldFeatureBits));
+
           std::string Buffer;
           raw_string_ostream OutputErrMsg(Buffer);
           handleAllErrors(ParseResult.takeError(), [&](llvm::StringError &ErrMsg) {
             OutputErrMsg << ErrMsg.getMessage();
           });
 
           return Error(Loc, OutputErrMsg.str());
         }

llvm/test/MC/RISCV/option-invalid.s

 .option arch, -f
 
 # CHECK: :[[#@LINE+1]]:16: error: Can't disable zicsr extension, f extension requires zicsr extension be enabled
 .option arch, -zicsr
 
 # CHECK: :[[#@LINE+1]]:20: error: 'f' and 'zfinx' extensions are incompatible
 .option arch, +f, +zfinx
 
+## Make sure the above error isn't sticky
+# CHECK-NOT: :[[#@LINE+1]]:
+.option arch, +f
+
 # CHECK: :[[#@LINE+1]]:13: error: expected newline
 .option rvc foo
 
 # CHECK: :[[#@LINE+1]]:12: warning: unknown option, expected 'push', 'pop', 'rvc', 'norvc', 'arch', 'relax' or 'norelax'
 .option bar
 
 # CHECK: :[[#@LINE+1]]:16: error: unknown extension feature
 .option arch, -i