[llvm] [RISCV] Remove unneeded zext.h instructions (PR #225960)

[via llvm-commits]

github-actions[bot] wrote:

test-suite diff from ea9f4c16ec59a210753b6e5dd23e6b0ee0a8542c...8030bb61fae4f7cecfb4415af7e81a49e94a03cf: https://github.com/llvm/llvm-project/actions/runs/35982639798/artifacts/10813078791

Statistics: https://github.com/llvm/llvm-project/actions/runs/35982639798/artifacts/10812759951

## riscv64-linux-gnu `-march=rva23u64 -O3`
| ('Program', '')    |   ('size..text', 'base') |   ('size..text', 'head') |   ('size..text', 'diff') |
|:-------------------|-------------------------:|-------------------------:|-------------------------:|
| ClamAV/clamscan    |                   379530 |                   379552 |              5.79664e-05 |
| JM/ldecod/ldecod   |                   230934 |                   230940 |              2.59814e-05 |
| Geomean difference |                      nan |                      nan |             -4.70475e-05 |
## aarch64-linux-gnu `-march=armv9-a -O3`
| ('Program', '')                             |   ('size..text', 'base') |   ('size..text', 'head') |   ('size..text', 'diff') |
|:--------------------------------------------|-------------------------:|-------------------------:|-------------------------:|
| Applications/ClamAV/clamscan                |                   488708 |                   488932 |              0.000458351 |
| Benchmarks/mafft/pairlocalalign             |                   361664 |                   361748 |              0.00023226  |
| Benchmarks...ataFlow-dbl/GlobalDataFlow-dbl |                    35292 |                    35296 |              0.00011334  |
| Benchmarks...ataFlow-flt/GlobalDataFlow-flt |                    39576 |                    39580 |              0.000101071 |
| Benchmarks...OE-ProxyApps-C/miniAMR/miniAMR |                    50776 |                    50780 |              7.87774e-05 |
| Geomean difference                          |                      nan |                      nan |              6.36377e-07 |
## x86_64-linux-gnu `-march=x86-64-v3 -O3`
| ('Program', '')    |   ('size..text', 'base') |   ('size..text', 'head') |   ('size..text', 'diff') |
|:-------------------|-------------------------:|-------------------------:|-------------------------:|
| Geomean difference |                      nan |                      nan |                        0 |


https://github.com/llvm/llvm-project/pull/225960