On Fri, Sep 8, 2023 at 1:49 AM Takayuki 'January June' Suwa <jjsuwa_sys3...@yahoo.co.jp> wrote: > > An idiomatic implementation of boolean evaluation of whether a register is > zero or not in Xtensa is to assign 0 and 1 to the temporary and destination, > and then issue the MOV[EQ/NE]Z machine instruction > (See 8.3.2 Instruction Idioms, Xtensa ISA refman., p.599): > > ;; A2 = (A3 != 0) ? 1 : 0; > movi.n a9, 1 > movi.n a2, 0 > movnez a2, a9, a3 ;; if (A3 != 0) A2 = A9; > > As you can see in the above idiom, if the source and destination are the > same register, a move instruction from the source to another temporary > register must be prepended: > > ;; A2 = (A2 == 0) ? 1 : 0; > mov.n a10, a2 > movi.n a9, 1 > movi.n a2, 0 > moveqz a2, a9, a10 ;; if (A10 == 0) A2 = A9; > > Fortunately, we can reduce the number of instructions and temporary > registers with a few tweaks: > > ;; A2 = (A3 != 0) ? 1 : 0; > movi.n a2, 1 > moveqz a2, a3, a3 ;; if (A3 == 0) A2 = A3; > > ;; A2 = (A2 != 0) ? 1 : 0; > movi.n a9, 1 > movnez a2, a9, a2 ;; if (A2 != 0) A2 = A9; > > ;; A2 = (A3 == 0) ? 1 : 0; > movi.n a2, -1 > moveqz a2, a3, a3 ;; if (A3 == 0) A2 = A3; > addi.n a2, a2, 1 > > ;; A2 = (A2 == 0) ? 1 : 0; > movi.n a9, -1 > movnez a2, a9, a2 ;; if (A2 != 0) A2 = A9; > addi.n a2, a2, 1 > > Additionally, if TARGET_NSA is configured, the fact that it returns 32 iff > the source of the NSAU machine instruction is 0, otherwise less than, can be > used in boolean evaluation of EQ comparison. > > ;; A2 = (A3 == 0) ? 1 : 0; > nsau a2, a3 ;; Source and destination can be the same register > srli a2, a2, 5 > > Furthermore, this patch also saves one instruction when determining whether > the ANDing with mask values in which 1s are lined up from the upper or lower > bit end (for example, 0xFFE00000 or 0x003FFFFF) is 0 or not. > > gcc/ChangeLog: > > * config/xtensa/xtensa.cc (xtensa_expand_scc): > Revert the changes from the last patch, as the work in the RTL > expansion pass is too far to determine the physical registers. > * config/xtensa/xtensa.md (*eqne_INT_MIN): Ditto. > (eq_zero_NSA, eqne_zero, *eqne_zero_masked_bits): New patterns. > --- > gcc/config/xtensa/xtensa.cc | 35 +---------- > gcc/config/xtensa/xtensa.md | 112 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 113 insertions(+), 34 deletions(-)
Regtested for target=xtensa-linux-uclibc, no new regressions. Committed to master. -- Thanks. -- Max
