[gcc r14-8821] AArch64: aarch64_class_max_nregs mishandles 64-bit structure modes [PR112577]

[gcc r14-8821] AArch64: aarch64_class_max_nregs mishandles 64-bit structure modes [PR112577]

[Tejas Belagod]

https://gcc.gnu.org/g:ca04e7a2e1b08ed02e22e2656ba6032099195856

commit r14-8821-gca04e7a2e1b08ed02e22e2656ba6032099195856
Author: Tejas Belagod <tejas.belagod@arm.com>
Date:   Thu Jan 11 12:37:06 2024 +0530

    AArch64: aarch64_class_max_nregs mishandles 64-bit structure modes [PR112577]
    
    The target hook aarch64_class_max_nregs returns the incorrect result for 64-bit
    structure modes like V31DImode or V41DFmode etc.  The calculation of the nregs
    is based on the size of AdvSIMD vector register for 64-bit modes which ought to
    be UNITS_PER_VREG / 2.  This patch fixes the register size.
    
    gcc/ChangeLog:
    
            PR target/112577
            * config/aarch64/aarch64.cc (aarch64_class_max_nregs): Handle 64-bit
            vector structure modes correctly.

Diff:
---
 gcc/config/aarch64/aarch64.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 4556b8dd5045..872393a82312 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -12961,6 +12961,8 @@ aarch64_class_max_nregs (reg_class_t regclass, machine_mode mode)
 	  && constant_multiple_p (GET_MODE_SIZE (mode),
 				  aarch64_vl_bytes (mode, vec_flags), &nregs))
 	return nregs;
+      if (vec_flags == (VEC_ADVSIMD | VEC_STRUCT | VEC_PARTIAL))
+	return GET_MODE_SIZE (mode).to_constant () / 8;
       return (vec_flags & VEC_ADVSIMD
 	      ? CEIL (lowest_size, UNITS_PER_VREG)
 	      : CEIL (lowest_size, UNITS_PER_WORD));