| Issue |
127237
|
| Summary |
[AArch64] LLVM 20 regression when generating NEON instructions for ARMv9-A with SVE disabled
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
ptosi
|
Hi,
we have noticed a regression between Clang v19.0.1 and Clang v20.0.0 when compiling code targeting NEON for ARMv9-A with SVE disabled.
The following:
```
#include <arm_neon.h>
uint16x8_t vec_fma(uint16x8_t a, uint16x8_t b, uint16_t c)
{
return vmlaq_n_u16(a, b, c);
}
```
compiles with
```
clang -target aarch64-linux-gnu -march=armv9.2-a -O2 -Xclang -target-feature -Xclang -sve -c "neon.c"
```
to
```
0000000000000000 <vec_fma>:
0: 4e020c02 dup v2.8h, w0
4: 4e619440 mla v0.8h, v2.8h, v1.8h
8: d65f03c0 ret
```
with (Android build)
```
Android (12833971, +pgo, +bolt, +lto, +mlgo, based on r536225) clang version 19.0.1 (https://android.googlesource.com/toolchain/llvm-project b3a530ec6537146650e42be89f1089e9a3588460)
```
However, the same invocation fails:
```
neon.c:4:9: error: always_inline function 'vmlaq_n_u16' requires target feature 'sve', but would be inlined into function 'vec_fma' that is compiled without support for 'sve'
4 | return vmlaq_n_u16(a, b, c);
| ^
```
with
```
Android (13016439, +pgo, +bolt, +lto, +mlgo, based on r547379) clang version 20.0.0 (https://android.googlesource.com/toolchain/llvm-project b718bcaf8c198c82f3021447d943401e3ab5bd54)
```
instead of generating the NEON instructions, as expected.
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