[llvm] [Exegesis][RISCV] Add initial RVV support (PR #128767)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> LLVM Buildbot has detected a new failure on builder `clang-s390x-linux` running on `systemz-1` while building `llvm` at step 5 "ninja check 1".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/42/builds/3471
> 
> Here is the relevant piece of the build log for the reference
> ```
> Step 5 (ninja check 1) failure: stage 1 checked (failure)
> ******************** TEST 'LLVM :: tools/llvm-exegesis/RISCV/rvv/filter.test' FAILED ********************
> Exit Code: 2
> 
> Command Output (stderr):
> --
> RUN: at line 1: /home/uweigand/sandbox/buildbot/clang-s390x-linux/stage1/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK     --riscv-filter-config='vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=100 | /home/uweigand/sandbox/buildbot/clang-s390x-linux/stage1/bin/FileCheck /home/uweigand/sandbox/buildbot/clang-s390x-linux/llvm/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
> + /home/uweigand/sandbox/buildbot/clang-s390x-linux/stage1/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK '--riscv-filter-config=vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=100
> + /home/uweigand/sandbox/buildbot/clang-s390x-linux/stage1/bin/FileCheck /home/uweigand/sandbox/buildbot/clang-s390x-linux/llvm/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
> PseudoVNCLIPU_WX_M1_MASK: Failed to produce any snippet via: instruction has tied variables, avoiding Read-After-Write issue, picking random def and use registers not aliasing each other, for uses, one unique register for each position
> FileCheck error: '<stdin>' is empty.
> FileCheck command line:  /home/uweigand/sandbox/buildbot/clang-s390x-linux/stage1/bin/FileCheck /home/uweigand/sandbox/buildbot/clang-s390x-linux/llvm/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
> 
> --
> 
> ********************
> ```

Mitigated by 23c41bf1d599fddb4c5ee5eee7a30b5fdaa7f1be

https://github.com/llvm/llvm-project/pull/128767