On Tue, Jan 9, 2024 at 11:19 AM Uros Bizjak <ubiz...@gmail.com> wrote: > > On Tue, Jan 9, 2024 at 11:06 AM Richard Biener <rguent...@suse.de> wrote: > > > > On Tue, 9 Jan 2024, Uros Bizjak wrote: > > > > > On Tue, Jan 9, 2024 at 10:44?AM Richard Biener <rguent...@suse.de> wrote: > > > > > > > > On Tue, 9 Jan 2024, Uros Bizjak wrote: > > > > > > > > > On Tue, Jan 9, 2024 at 9:58?AM Richard Biener <rguent...@suse.de> > > > > > wrote: > > > > > > > > > > > > On Mon, 8 Jan 2024, Uros Bizjak wrote: > > > > > > > > > > > > > On Mon, Jan 8, 2024 at 5:57?PM Andrew Pinski <pins...@gmail.com> > > > > > > > wrote: > > > > > > > > > > > > > > > > On Mon, Jan 8, 2024 at 6:44?AM Uros Bizjak <ubiz...@gmail.com> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > Instead of converting XOR or PLUS of two values, ANDed with > > > > > > > > > two constants that > > > > > > > > > have no bits in common, to IOR expression, convert IOR or XOR > > > > > > > > > of said two > > > > > > > > > ANDed values to PLUS expression. > > > > > > > > > > > > > > > > I think this only helps targets which have leal like > > > > > > > > instruction. Also > > > > > > > > I think it is the same issue as I recorded as PR 111763 . I > > > > > > > > suspect > > > > > > > > BIT_IOR is more of a Canonical form for GIMPLE while we should > > > > > > > > handle > > > > > > > > this in expand to decide if we want to use PLUS or IOR. > > > > > > > > > > > > > > For the pr108477.c testcase, expand pass expands: > > > > > > > > > > > > > > r_3 = a_2(D) & 1; > > > > > > > p_5 = b_4(D) & 4294967292; > > > > > > > _1 = r_3 | p_5; > > > > > > > _6 = _1 + 2; > > > > > > > return _6; > > > > > > > > > > > > > > The transformation ( | -> + ) is valid only when CST1 & CST2 == > > > > > > > 0, so > > > > > > > we need to determine values of constants. Is this information > > > > > > > available in the expand pass? > > > > > > > > > > > > If there's single-uses then TER makes this info available. > > > > > > > > > > > > > IMO, the transformation from (ra | rb | cst) to (ra + rb + cst) > > > > > > > as in > > > > > > > the shown testcase would be beneficial when constructing control > > > > > > > register values (see e.g. mesa-3d). We can use LEA instead of > > > > > > > OR+ADD > > > > > > > sequence in this case. > > > > > > > > > > > > The other possibility is to expose LEA as optab and making GIMPLE > > > > > > instruction selection generate a direct internal function for that > > > > > > (that would be the "better" way). There is LEA-like &TARGET_MEM_REF > > > > > > but that has constraints on the addends mode (ptr_mode) which might > > > > > > not fit what the target can do? Otherwise that would be an existing > > > > > > way to do this computation as well. > > > > > > > > > > I think there is no need for a new optab. If we can determine at > > > > > expand time that ANDed values are fed to the IOR/XOR expressions, then > > > > > we can check the constants and emit PLUS RTX instead. RTL combine pass > > > > > will then create LEA instruction from separate PLUS instructions. > > > > > > > > > > So, we can emit: > > > > > > > > > > op0 = and (a, CST1) > > > > > op1 = and (b, CST2) > > > > > op2 = plus (op0, op1) > > > > > > > > > > RTX sequence for (a & CST1) | (b & CST2) when CST1 & CST2 == 0 > > > > > > > > > > and > > > > > > > > > > op0 = and (a, CST1) > > > > > op1 = plus (op0, CST2) > > > > > > > > > > RTX sequence for (a & CST1) | CST2 when CST1 & CST2 == 0 > > > > > > > > > > The above transformation is valid for IOR and XOR. > > > > > > > > > > x86 can't combine IOR/XOR in any meaningful way, but can combine the > > > > > sequence of PLUS (together with MULT) RTXes to LEA. > > > > > > > > Btw, this looks like a three-insn combination even with IOR so a > > > > pattern for this case would work as well? > > > > > > IIUC the question: x86 does not have three-input IOR, but we want to > > > emulate it with LEA (three-input PLUS, but one of the arguments has to > > > be constant). > > > > But couldn't you have a define_insn matching LEA but with IOR instead > > of PLUS (and with the appropriate constraints?). Maybe it could > > also be combine trying PLUS instead of IOR if that's possible > > (looking at the constants). > > we would have to include masking ANDs in the define_insn and add > additional conditions regarding mask constants in the insn constraint. > > So, this define_insn would look something like: > > (ior (ior (and (op1, CST1), and (op2, CST2)), CST3)) > > with (CST1 & CST2 & CST3) == 0 condition. > > and combinations with PLUS / MULT RTXes including all the variants > with two arguments.
Oh, and then we would have to split masking ANDs out of the above instruction. We can't clobber the inputs, so this should be made with a temporary registers before reload... Uros.
