The following patch introduces {add,sub}c5_optab and pattern recognizes
various forms of add with carry and subtract with carry/borrow, see
pr79173-{1,2,3,4,5,6}.c tests on what is matched.
Primarily forms with 2 __builtin_add_overflow or __builtin_sub_overflow
calls per limb (with just one for the least significant one), for
add with carry even when it is hand written in C (for subtraction
reassoc seems to change it too much so that the pattern recognition
doesn't work). __builtin_{add,sub}_overflow are standardized in C23
under ckd_{add,sub} names, so it isn't any longer a GNU only extension.
Note, clang has for these (IMHO badly designed)
__builtin_{add,sub}c{b,s,,l,ll} builtins which don't add/subtract just
a single bit of carry, but basically add 3 unsigned values or
subtract 2 unsigned values from one, and result in carry out of 0, 1, or 2
because of that. If we wanted to introduce those for clang compatibility,
we could and lower them early to just two __builtin_{add,sub}_overflow
calls and let the pattern matching in this patch recognize it later.
I've added expanders for this on ix86 and in addition to that
added various peephole2s (in preparation patches for this patch) to make
sure we get nice (and small) code for the common cases. I think there are
other PRs which request that e.g. for the _{addcarry,subborrow}_u{32,64}
intrinsics, which the patch also improves.
Would be nice if support for these optabs was added to many other targets,
arm/aarch64 and powerpc* certainly have such instructions, I'd expect
in fact that most targets do.
The _BitInt support I'm working on will also need this to emit reasonable
code.
2023-06-15 Jakub Jelinek <jakub@redhat.com>
PR middle-end/79173
* internal-fn.def (UADDC, USUBC): New internal functions.
* internal-fn.cc (expand_UADDC, expand_USUBC): New functions.
(commutative_ternary_fn_p): Return true also for IFN_UADDC.
* optabs.def (uaddc5_optab, usubc5_optab): New optabs.
* tree-ssa-math-opts.cc (uaddc_cast, uaddc_ne0, uaddc_is_cplxpart,
match_uaddc_usubc): New functions.
(math_opts_dom_walker::after_dom_children): Call match_uaddc_usubc
for PLUS_EXPR, MINUS_EXPR, BIT_IOR_EXPR and BIT_XOR_EXPR unless
other optimizations have been successful for those.
* gimple-fold.cc (gimple_fold_call): Handle IFN_UADDC and IFN_USUBC.
* fold-const-call.cc (fold_const_call): Likewise.
* gimple-range-fold.cc (adjust_imagpart_expr): Likewise.
* tree-ssa-dce.cc (eliminate_unnecessary_stmts): Likewise.
* doc/md.texi (uaddc<mode>5, usubc<mode>5): Document new named
patterns.
* config/i386/i386.md (uaddc<mode>5, usubc<mode>5): New
define_expand patterns.
(*setcc_qi_addqi3_cconly_overflow_1_<mode>, *setccc): Split
into NOTE_INSN_DELETED note rather than nop instruction.
(*setcc_qi_negqi_ccc_1_<mode>, *setcc_qi_negqi_ccc_2_<mode>):
Likewise.
* gcc.target/i386/pr79173-1.c: New test.
* gcc.target/i386/pr79173-2.c: New test.
* gcc.target/i386/pr79173-3.c: New test.
* gcc.target/i386/pr79173-4.c: New test.
* gcc.target/i386/pr79173-5.c: New test.
* gcc.target/i386/pr79173-6.c: New test.
* gcc.target/i386/pr79173-7.c: New test.
* gcc.target/i386/pr79173-8.c: New test.
* gcc.target/i386/pr79173-9.c: New test.
* gcc.target/i386/pr79173-10.c: New test.
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