https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114801
--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Christophe Lyon from comment #12) > (In reply to Jakub Jelinek from comment #11) > > So, tried this under the debugger. All VALID_MVE_PRED_MODE modes have the > > same size, 2 bytes, so I'd go with > > else if (VALID_MVE_PRED_MODE (mode)) > > { > > /* unsigned short arguments to functions get promoted to int, undo > > that. */ > > if (GET_MODE_SIZE (x) != GET_MODE_SIZE (HImode)) > > x = gen_lowpart (HImode, x); > > if (GET_MODE (x) != mode) > > { > > /* Nested SUBREGs are invalid. */ > > if (SUBREG_P (x)) > > x = force_reg (GET_MODE (x), x); > > x = lowpart_subreg (mode, x, > > GET_MODE (x) == VOIDmode ? HImode : GET_MODE > > (x)); > > This still crashes with mode == V*BI, because we reach > rtx_vector_builder::find_cached_value() where elt is not a supported > constant. Ah, I was testing just V16BImode and V8BImode, with V16BImode even just gen_lowpart on (const_int -13108 [0xffffffffffffcccc]) works and gives (const_vector:V16BI [ (const_int 0 [0]) repeated x2 (const_int 1 [0x1]) repeated x2 (const_int 0 [0]) repeated x2 (const_int 1 [0x1]) repeated x2 (const_int 0 [0]) repeated x2 (const_int 1 [0x1]) repeated x2 (const_int 0 [0]) repeated x2 (const_int 1 [0x1]) repeated x2 ]) while for V8BImode it gives (const_vector:V8BI [ (const_int 0 [0]) (const_int -1 [0xffffffffffffffff]) (const_int 0 [0]) (const_int -1 [0xffffffffffffffff]) (const_int 0 [0]) (const_int -1 [0xffffffffffffffff]) (const_int 0 [0]) (const_int -1 [0xffffffffffffffff]) ]) Now, the question is what these weird B2Imode and B4Imode modes are about. Are they really 2bit and 4bit booleans, with 0 being false, some value (1 or all ones?) true, everything else UB? Something else? The 0xcccc when it is 1 bit per element indeed is what the above V16BImode CONST_VECTOR is, the 0xcccc with 2 bits per element is 0 or -1 (but, shouldn't that be UB?), but with 0xcccc with 4 bits per element it is element 0xc, that doesn't feel right for a boolean in any case. native_decode_vector_rtx for the bool vectors does: unsigned int bit_index = first_byte * BITS_PER_UNIT + i * elt_bits; unsigned int byte_index = bit_index / BITS_PER_UNIT; unsigned int lsb = bit_index % BITS_PER_UNIT; unsigned int value = bytes[byte_index] >> lsb; builder.quick_push (gen_int_mode (value, GET_MODE_INNER (mode))); and kind of expects that gen_int_mode canonicalizes it to some boolean value (apparently it can handle both all ones and 1 as true, but not other values). 93 if (elt == const1_rtx) 94 return CONST1_RTX (m_mode); 95 else if (elt == constm1_rtx) 96 return CONSTM1_RTX (m_mode); 97 else if (elt == const0_rtx) 98 return CONST0_RTX (m_mode); 99 else 100 gcc_unreachable (); Guess you can get similar ICE for V8BImode if some 2 bit pair is 2 (3 and 1 are considered true, one of them -1, another 1) and 0 is false; and for V4BImode obviously far more invalid values. If the CPU somehow canonicalizes, say any non-zero 2-bit pair (or 4-bit pair) is considered true (or say decide just based on most significant or least significant bit), then perhaps you need to do that canonicalization by hand.