GCC modified for the FreeChainXenon project
35f4e95265
This patch completes the ARC back-end's transition to using pre-reload
splitters for SImode shifts and rotates on targets without a barrel
shifter. The core part is that the shift_si3 define_insn is no longer
needed, as shifts and rotates that don't require a loop are split
before reload, and then because shift_si3_loop is the only caller
of output_shift, both can be significantly cleaned up and simplified.
The output_shift function (Claudiu's "the elephant in the room") is
renamed output_shift_loop, which handles just the four instruction
zero-overhead loop implementations.
Aside from the clean-ups, the user visible changes are much improved
implementations of SImode shifts and rotates on affected targets.
For the function:
unsigned int rotr_1 (unsigned int x) { return (x >> 1) | (x << 31); }
GCC with -O2 -mcpu=em would previously generate:
rotr_1: lsr_s r2,r0
bmsk_s r0,r0,0
ror r0,r0
j_s.d [blink]
or_s r0,r0,r2
with this patch, we now generate:
j_s.d [blink]
ror r0,r0
For the function:
unsigned int rotr_31 (unsigned int x) { return (x >> 31) | (x << 1); }
GCC with -O2 -mcpu=em would previously generate:
rotr_31:
mov_s r2,r0 ;4
asl_s r0,r0
add.f 0,r2,r2
rlc r2,0
j_s.d [blink]
or_s r0,r0,r2
with this patch we now generate an add.f followed by an adc:
rotr_31:
add.f r0,r0,r0
j_s.d [blink]
add.cs r0,r0,1
Shifts by constants requiring a loop have been improved for even counts
by performing two operations in each iteration:
int shl10(int x) { return x >> 10; }
Previously looked like:
shl10: mov.f lp_count, 10
lpnz 2f
asr r0,r0
nop
2: # end single insn loop
j_s [blink]
And now becomes:
shl10:
mov lp_count,5
lp 2f
asr r0,r0
asr r0,r0
2: # end single insn loop
j_s [blink]
So emulating ARC's SWAP on architectures that don't have it:
unsigned int rotr_16 (unsigned int x) { return (x >> 16) | (x << 16); }
previously required 10 instructions and ~70 cycles:
rotr_16:
mov_s r2,r0 ;4
mov.f lp_count, 16
lpnz 2f
add r0,r0,r0
nop
2: # end single insn loop
mov.f lp_count, 16
lpnz 2f
lsr r2,r2
nop
2: # end single insn loop
j_s.d [blink]
or_s r0,r0,r2
now becomes just 4 instructions and ~18 cycles:
rotr_16:
mov lp_count,8
lp 2f
ror r0,r0
ror r0,r0
2: # end single insn loop
j_s [blink]
2023-10-24 Roger Sayle <roger@nextmovesoftware.com>
Claudiu Zissulescu <claziss@gmail.com>
gcc/ChangeLog
* config/arc/arc-protos.h (output_shift): Rename to...
(output_shift_loop): Tweak API to take an explicit rtx_code.
(arc_split_ashl): Prototype new function here.
(arc_split_ashr): Likewise.
(arc_split_lshr): Likewise.
(arc_split_rotl): Likewise.
(arc_split_rotr): Likewise.
* config/arc/arc.cc (output_shift): Delete local prototype. Rename.
(output_shift_loop): New function replacing output_shift to output
a zero overheap loop for SImode shifts and rotates on ARC targets
without barrel shifter (i.e. no hardware support for these insns).
(arc_split_ashl): New helper function to split *ashlsi3_nobs.
(arc_split_ashr): New helper function to split *ashrsi3_nobs.
(arc_split_lshr): New helper function to split *lshrsi3_nobs.
(arc_split_rotl): New helper function to split *rotlsi3_nobs.
(arc_split_rotr): New helper function to split *rotrsi3_nobs.
(arc_print_operand): Correct whitespace.
(arc_rtx_costs): Likewise.
(hwloop_optimize): Likewise.
* config/arc/arc.md (ANY_SHIFT_ROTATE): New define_code_iterator.
(define_code_attr insn): New code attribute to map to pattern name.
(<ANY_SHIFT_ROTATE>si3): New expander unifying previous ashlsi3,
ashrsi3 and lshrsi3 define_expands. Adds rotlsi3 and rotrsi3.
(*<ANY_SHIFT_ROTATE>si3_nobs): New define_insn_and_split that
unifies the previous *ashlsi3_nobs, *ashrsi3_nobs and *lshrsi3_nobs.
We now call arc_split_<insn> in arc.cc to implement each split.
(shift_si3): Delete define_insn, all shifts/rotates are now split.
(shift_si3_loop): Rename to...
(<insn>si3_loop): define_insn to handle loop implementations of
SImode shifts and rotates, calling ouput_shift_loop for template.
(rotrsi3): Rename to...
(*rotrsi3_insn): define_insn for TARGET_BARREL_SHIFTER's ror.
(*rotlsi3): New define_insn_and_split to transform left rotates
into right rotates before reload.
(rotlsi3_cnt1): New define_insn_and_split to implement a left
rotate by one bit using an add.f followed by an adc.
* config/arc/predicates.md (shiftr4_operator): Delete.
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