[Bug target/116150] New: RISC-V: Differences between GCC/LLVM

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116150

            Bug ID: 116150
           Summary: RISC-V: Differences between GCC/LLVM
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at rivosinc dot com
  Target Milestone: ---

A byproduct of my first sweep through the ISA strings with a random generator.
Extensions were seeded with -print-supported-exts from a few days ago. Ignored
profiles, experimental extensions, and extension versions. This isn't
guaranteed to be a complete list.

ilp32e 'd' extension handling:
https://inbox.sourceware.org/gcc-patches/20240730213254.199844-1-patrick@rivosinc.com/T/#u

Implied extensions:
LLVM zabha does not imply zaamo, gcc does: https://godbolt.org/z/nd6jz1vbc
LLVM all zvk* throw this error: "'zvk*' requires 'v' or 'zve*' extension to
also be specified" on GCC v is implied: https://godbolt.org/z/Pb9KWr9Y8

Unsupported (LLVM-only exts):
shcounterenw
shgatpa
shtvala
shvsatpa
shvstvala
shvstvecd
smcdeleg
smcsrind
ssccfg
ssccptr
sscounterenw
sscsrind
ssstrict
sstvala
sstvecd
ssu64xl
svade
svadu
svbare
xcvbitmanip
xcvmem
xsfvfnrclipxfqf
xsfvfwmaccqqq
xsfvqmaccdod
xsfvqmaccqoq
xsifivecdiscarddlone
xsifivecflushdlone
xtheadvdot
xwchc
zama16b
zcmop
zimop

Supported by GCC, unsupported by LLVM:
xtheadfmv
xtheadint
xtheadvector