On Mon, Nov 25, 2024 at 10:39 AM Jakub Jelinek <ja...@redhat.com> wrote: > > On Sun, Nov 24, 2024 at 10:02:22PM +0100, Uros Bizjak wrote: > > PR target/36503 > > > > gcc/ChangeLog: > > > > * config/i386/i386.md (*ashl<mode>3_negcnt): > > New define_insn_and_split pattern. > > (*ashl<mode>3_negcnt_1): Ditto. > > (*<insn><mode>3_negcnt): Ditto. > > (*<insn><mode>3_negcnt_1): Ditto. > > > > gcc/testsuite/ChangeLog: > > > > * gcc.target/i386/pr36503-1.c: New test. > > * gcc.target/i386/pr36503-2.c: New test. > > > +(define_insn_and_split "*ashl<mode>3_negcnt" > > + [(set (match_operand:SWI48 0 "nonimmediate_operand") > > + (ashift:SWI48 > > + (match_operand:SWI48 1 "nonimmediate_operand") > > + (subreg:QI > > + (minus > > + (match_operand 3 "const_int_operand") > > + (match_operand 2 "int248_register_operand" "c,r")) 0))) > > + (clobber (reg:CC FLAGS_REG))] > > + "ix86_binary_operator_ok (ASHIFT, <MODE>mode, operands) > > + && INTVAL (operands[3]) == <MODE_SIZE> * BITS_PER_UNIT > > Any reason for an exact comparison rather than > && (INTVAL (operands[3]) & (<MODE_SIZE> * BITS_PER_UNIT - 1)) == 0 > ? > I mean, we can optimize this way 1U << (32 - x) or > 1U << (1504 - x) or any other multiply of 32.
Count values outside of [0, bitwidth) are undefined in general. Also, during the bootstrap only values of 32 or 64 were found, so I thought to not complicate the condition too much FYI, the conversion triggers 504 times during the bootstrap, I somehow expected a lower number. > Similarly, we can optimize 1U << (32 + x) to 1U << x and > again do that for any other multiplies of 32. I don't think anybody uses the above idiom, it is valid only for certain targets (x86 and the ones that mask count argument), but undefined in general. Uros.
