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

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-with-thin-lto-ubuntu` running on `as-worker-92` while building `llvm` at step 7 "test-stage1-compiler".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/127/builds/2556

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-stage1-compiler) failure: build (failure)
...
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:512: note: using ld64.lld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/ld64.lld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:512: note: using wasm-ld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/wasm-ld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/utils/lit/tests/lit.cfg:111: warning: Setting a timeout per test not supported. Requires the Python psutil module but it could not be found. Try installing it via pip or via your operating system's package manager.
 Some tests will be skipped and the --timeout command line argument will not work.
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:512: note: using ld.lld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/ld.lld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:512: note: using lld-link: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/lld-link
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:512: note: using ld64.lld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/ld64.lld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:512: note: using wasm-ld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/wasm-ld
-- Testing: 83875 tests, 72 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80..
FAIL: LLVM :: tools/llvm-exegesis/RISCV/rvv/reduction.test (74191 of 83875)
******************** TEST 'LLVM :: tools/llvm-exegesis/RISCV/rvv/reduction.test' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVWREDSUMU_VS_M8_E32 --min-instructions=100 |     /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/FileCheck /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/reduction.test
+ /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVWREDSUMU_VS_M8_E32 --min-instructions=100
+ /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/FileCheck /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/reduction.test
/home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/reduction.test:7:14: error: CHECK-NOT: excluded string found in input
# CHECK-NOT: V[[REG:[0-9]+]] V[[REG]] V{{[0-9]+}}M8 V[[REG]]
             ^
<stdin>:5:31: note: found here
 - 'PseudoVWREDSUMU_VS_M8_E32 V9 V9 V8M8 V9 i_0xffffffffffffffff i_0x5 i_0x0'
                              ^~~~~~~~~~~~~
<stdin>:5:32: note: captured var "REG"
 - 'PseudoVWREDSUMU_VS_M8_E32 V9 V9 V8M8 V9 i_0xffffffffffffffff i_0x5 i_0x0'
                               ^

Input file: <stdin>
Check file: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/reduction.test

-dump-input=help explains the following input dump.

Input was:
<<<<<<
         1: --- 
         2: mode: latency 
         3: key: 
         4:  instructions: 
         5:  - 'PseudoVWREDSUMU_VS_M8_E32 V9 V9 V8M8 V9 i_0xffffffffffffffff i_0x5 i_0x0' 
not:7'0                                   !~~~~~~~~~~~~                                    error: no match expected
not:7'1                                    !                                               captured var "REG"
         6:  config: 'vtype = {AVL: VLMAX, SEW: e32, Policy: tu/mu}' 
         7:  register_initial_values: 
         8:  - 'V9=0x0' 
         9:  - 'V8M8=0x0' 
        10: cpu_name: sifive-p670 
         .

```

</details>

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