https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112415
--- Comment #47 from dave.anglin at bell dot net --- On 2023-11-13 4:33 a.m., manolis.tsamis at vrull dot eu wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112415 > > --- Comment #44 from Manolis Tsamis <manolis.tsamis at vrull dot eu> --- > (In reply to John David Anglin from comment #39) >> In the f-m-o pass, the following three insns that set call clobbered >> registers r20-r22 are pulled from loop: >> >> (insn 186 183 190 29 (set (reg/f:SI 22 %r22 [478]) >> (plus:SI (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127]) >> (const_int 388 [0x184]))) "../Python/compile.c":5964:9 120 >> {addsi3} >> (nil)) >> (insn 190 186 187 29 (set (reg/f:SI 21 %r21 [479]) >> (plus:SI (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127]) >> (const_int 392 [0x188]))) "../Python/compile.c":5964:9 120 >> {addsi3} >> (nil)) >> (insn 194 191 195 29 (set (reg/f:SI 20 %r20 [480]) >> (plus:SI (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127]) >> (const_int 396 [0x18c]))) "../Python/compile.c":5964:9 120 >> {addsi3} >> (nil)) >> >> They are used in the following insns before call to compiler_visit_expr1: >> >> (insn 242 238 258 32 (set (mem:SI (reg/f:SI 22 %r22 [478]) [4 MEM[(int >> *)prephit >> mp_37 + 388B]+0 S4 A32]) >> (reg:SI 23 %r23 [orig:173 vect__102.2442 ] [173])) >> "../Python/compile.c" >> :5968:22 42 {*pa.md:2193} >> (expr_list:REG_DEAD (reg:SI 23 %r23 [orig:173 vect__102.2442 ] [173]) >> (expr_list:REG_DEAD (reg/f:SI 22 %r22 [478]) >> (nil)))) >> (insn 258 242 246 32 (set (reg:SI 26 %r26) >> (reg/v/f:SI 5 %r5 [orig:198 c ] [198])) >> "../Python/compile.c":5969:15 42 {*pa.md:2193} >> (nil)) >> (insn 246 258 250 32 (set (mem:SI (reg/f:SI 21 %r21 [479]) [4 MEM[(int >> *)prephitmp_37 + 392B]+0 S4 A32]) >> (reg:SI 29 %r29 [orig:169 vect__102.2443 ] [169])) >> "../Python/compile.c":5968:22 42 {*pa.md:2193} >> (expr_list:REG_DEAD (reg:SI 29 %r29 [orig:169 vect__102.2443 ] [169]) >> (expr_list:REG_DEAD (reg/f:SI 21 %r21 [479]) >> (nil)))) >> (insn 250 246 254 32 (set (mem:SI (reg/f:SI 20 %r20 [480]) [4 MEM[(int >> *)prephitmp_37 + 396B]+0 S4 A32]) >> (reg:SI 31 %r31 [orig:145 vect__102.2444 ] [145])) >> "../Python/compile.c":5968:22 42 {*pa.md:2193} >> (expr_list:REG_DEAD (reg:SI 31 %r31 [orig:145 vect__102.2444 ] [145]) >> (expr_list:REG_DEAD (reg/f:SI 20 %r20 [480]) >> (nil)))) >> >> After the call, we have: >> >> (insn 1241 269 273 30 (set (reg/f:SI 22 %r22 [478]) >> (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127])) >> "../Python/compile.c":5970:20 -1 >> (nil)) >> (insn 273 1241 1242 30 (set (mem:SI (plus:SI (reg/f:SI 22 %r22 [478]) >> (const_int 388 [0x184])) [4 MEM[(int *)_107 + 388B]+0 S4 >> A32]) >> (reg:SI 14 %r14 [orig:167 vect_pretmp_36.2450 ] [167])) >> "../Python/compile.c":5970:20 42 {*pa.md:2193} >> (nil)) >> (insn 1242 273 277 30 (set (reg/f:SI 21 %r21 [479]) >> (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127])) >> "../Python/compile.c":5970:20 -1 >> (nil)) >> (insn 277 1242 1243 30 (set (mem:SI (plus:SI (reg/f:SI 21 %r21 [479]) >> (const_int 392 [0x188])) [4 MEM[(int *)_107 + 392B]+0 S4 >> A32]) >> (reg:SI 13 %r13 [orig:156 vect_pretmp_36.2451 ] [156])) >> "../Python/compile.c":5970:20 42 {*pa.md:2193} >> (nil)) >> (insn 1243 277 281 30 (set (reg/f:SI 20 %r20 [480]) >> (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127])) >> "../Python/compile.c":5970:20 -1 >> (nil)) >> (insn 281 1243 299 30 (set (mem:SI (plus:SI (reg/f:SI 20 %r20 [480]) >> (const_int 396 [0x18c])) [4 MEM[(int *)_107 + 396B]+0 S4 >> A32]) >> (reg:SI 12 %r12 [orig:134 vect_pretmp_36.2452 ] [134])) >> "../Python/compile.c":5970:20 42 {*pa.md:2193} >> (nil)) >> >> We have lost the offsets that were added initially to r20, r21 and r22. >> >> Previous ce3 pass had: >> >> (insn 272 269 273 30 (set (reg/f:SI 22 %r22 [478]) >> (plus:SI (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127]) >> (const_int 388 [0x184]))) "../Python/compile.c":5970:20 120 >> {addsi3} >> (nil)) >> (insn 273 272 276 30 (set (mem:SI (reg/f:SI 22 %r22 [478]) [4 MEM[(int >> *)_107 + 388B]+0 S4 A32]) >> (reg:SI 14 %r14 [orig:167 vect_pretmp_36.2450 ] [167])) >> "../Python/compile.c":5970:20 42 {*pa.md:2193} >> (nil)) >> (insn 276 273 277 30 (set (reg/f:SI 21 %r21 [479]) >> (plus:SI (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127]) >> (const_int 392 [0x188]))) "../Python/compile.c":5970:20 120 >> {addsi3} >> (nil)) >> (insn 277 276 280 30 (set (mem:SI (reg/f:SI 21 %r21 [479]) [4 MEM[(int >> *)_107 + 392B]+0 S4 A32]) >> (reg:SI 13 %r13 [orig:156 vect_pretmp_36.2451 ] [156])) >> "../Python/compile.c":5970:20 42 {*pa.md:2193} >> (nil)) >> (insn 280 277 281 30 (set (reg/f:SI 20 %r20 [480]) >> (plus:SI (reg/f:SI 19 %r19 [orig:127 prephitmp_37 ] [127]) >> (const_int 396 [0x18c]))) "../Python/compile.c":5970:20 120 >> {addsi3} >> (nil)) >> (insn 281 280 284 30 (set (mem:SI (reg/f:SI 20 %r20 [480]) [4 MEM[(int >> *)_107 + 396B]+0 S4 A32]) >> (reg:SI 12 %r12 [orig:134 vect_pretmp_36.2452 ] [134])) >> "../Python/compile.c":5970:20 42 {*pa.md:2193} >> (nil)) >> >> So, this is a f-m-o bug. > Hi Dave, > > I don't see an f-m-o bug here. The offsets aren't lost, they're just moved in > the corresponding memory loads/stores. If you look the stores in ce3 they > don't have offsets whereas after f-m-o they have. E.g. in ce3: (insn 273 272 > 276 30 (set (mem:SI (reg/f:SI 22 %r22 [478]) ...) but in f-m-o it is (insn 273 > 1241 1242 30 (set (mem:SI (plus:SI (reg/f:SI 22 %r22 [478]) (const_int 388 > [0x184]) ...). > > This is the way that f-m-o works. It can also be seen in the f-m-o dumps, > where > offsets changes to memory ops are reported as 'Memory offset changed' and > instructions which got their offset propagated (like insns 272, 276, 280) are > reported as 'Instruction folded': Hi Manolis, If you look at the f-m-o transformation applied to insn 272 and insn 273, you will see that "reg/f:SI 22 %r22 [478]" is not dead after these insns. The transformation changes the value of r22 which is wrong without changing all uses of the register and adjusting the other sets for the register. It only changed the use in insn 273 and not the uses earlier in the loop.
