https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114966
--- Comment #5 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
I saw pass_eras optimize BIT_FIELD_REF of big memory into load from small
memory
Created a replacement for D.161366 offset: 0, size: 64: SR.20D.170101
Created a replacement for D.161366 offset: 64, size: 64: SR.21D.170102
Created a replacement for D.161366 offset: 128, size: 64: SR.22D.170103
Created a replacement for D.161547 offset: 0, size: 256: SR.23D.170104
_8 = BIT_FIELD_REF <MEM[(const struct _SimdWrapper
*)&D.159286].D.158970._M_data, 64, 0>;
_9 = BIT_FIELD_REF <MEM[(const struct _SimdWrapper
*)&D.159286].D.158970._M_data, 64, 64>;
_10 = BIT_FIELD_REF <MEM[(const struct _SimdWrapper
*)&D.159286].D.158970._M_data, 64, 128>;
_11 = {0, _8, _9, _10};
to
SR.20_3 = MEM <const long unsigned int> [(struct simd *)&data];
SR.21_13 = MEM <const long unsigned int> [(struct simd *)&data + 8B];
SR.22_14 = MEM <const long unsigned int> [(struct simd *)&data + 16B];
_7 = SR.20_3;
_8 = SR.21_13;
_9 = SR.22_14;
_10 = {0, _7, _8, _9};
So I guess for the later GCC somehow can't be sure the whole 256-bit memory is
valid and fail to optimize it with vec_perm_expr?
