Thank you so much for the fast reply. Ok, it is true that I didn't think about it carefully. Can you help me with the following the issue?
For RVV (RISC-V 'V' Extension), we have full vector type 'vint8m1_t' (LMUL = 1) and fractional vector type 'vint8mf2_t' (LMUL = 1/2). Because in the ISA, we don't have whole register load/store for fractional vector. I reference the LLVM implementation and I adjust BITSIZE of fractional vector same as full vector (It will confuse GCC the bytesize of fractional vector and consider the spill size of a fractional vector is same as LMUL = 1) so that I can use whole register load/store directly during the register spilling. (Even though it will enlarge the spill size). According to the machine_mode definition, The machine_mode PRECISION is calculate by component size which is different from BITSIZE Now, here is the question. For array type: vint8mf2x4_t, if I want to access vint8mf2x4_t[2], because the PRECISION and BITSIZE are different. Because bitops is calculated by bitsize and compare to precision in the codes that the patch mentioned. It will make a out-of-bounds access to small array. Can you help me with this? This is important for the following RVV upstream support. Thanks. juzhe.zh...@rivai.ai From: Richard Biener Date: 2022-07-27 14:46 To: zhongjuzhe CC: gcc-patches; richard.earnshaw; jakub; kenner; jlaw; gnu; jason; davem; joseph; richard.sandiford; bernds_cb1; ian; wilson Subject: Re: [PATCH 1/1] Fix bit-position comparison On Wed, 27 Jul 2022, juzhe.zh...@rivai.ai wrote: > From: zhongjuzhe <juzhe.zh...@rivai.ai> > > gcc/ChangeLog: > > * expr.cc (expand_assignment): Change GET_MODE_PRECISION to > GET_MODE_BITSIZE > > --- > gcc/expr.cc | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/gcc/expr.cc b/gcc/expr.cc > index 80bb1b8a4c5..ac2b3c07df6 100644 > --- a/gcc/expr.cc > +++ b/gcc/expr.cc > @@ -5574,7 +5574,7 @@ expand_assignment (tree to, tree from, bool nontemporal) > code contains an out-of-bounds access to a small array. */ > if (!MEM_P (to_rtx) > && GET_MODE (to_rtx) != BLKmode > - && known_ge (bitpos, GET_MODE_PRECISION (GET_MODE (to_rtx)))) > + && known_ge (bitpos, GET_MODE_BITSIZE (GET_MODE (to_rtx)))) I think this has the chance to go wrong with regard to endianess. Consider to_rtx with 32bit mode size but 12bit mode precision. bitpos is relative to the start of to_rtx as if it were in memory and bitsize determines the contiguous region affected. But since we are actually storing into a non-memory endianess comes into play. So no, I don't think the patch is correct, it would be way more complicated to get the desired improvement. Richard. > { > expand_normal (from); > result = NULL; > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)