https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116778
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Denis Chertykov <den...@gcc.gnu.org>: https://gcc.gnu.org/g:279b3c71702de150eade19635bdbd26ba440b8eb commit r15-6008-g279b3c71702de150eade19635bdbd26ba440b8eb Author: Denis Chertykov <cherty...@gmail.com> Date: Sat Dec 7 13:47:04 2024 +0400 The fix for PR116778: Brief: The bug appears in LRA after rematerialization pass while creating live ranges. File lra.cc: ************************************************************* /* Now we know what pseudos should be spilled. Try to rematerialize them first. */ if (lra_remat ()) { /* We need full live info -- see the comment above. */ lra_create_live_ranges (lra_reg_spill_p, true); ************************************************************* Wrong call `lra_create_live_ranges (lra_reg_spill_p, true)' It have to be `lra_create_live_ranges (true, true)'. The explanation: ********************************** int main (void) { if (a.u33 * a.u33 != 0) ------^^^^^^^^^^^^^ goto abrt; if (a.u33 * a.u40 * a.u33 != 0) ********************************** The bug appears here. Part of the expression `a.u33 * a.u33' Before LRA: ************************************************************* (insn 13 11 15 2 (set (reg:QI 184 [ _1+3 ]) (mem/c:QI (const:HI (plus:HI (symbol_ref:HI ("a") [flags 0x2] <var_decl 0x7c866435d000 a>) (const_int 3 [0x3]))) [1 a+3 S1 A8])) "bf.c":11:8 86 {movqi_insn_split} (nil)) (insn 15 13 16 2 (set (reg:QI 64 [ a+4 ]) (mem/c:QI (const:HI (plus:HI (symbol_ref:HI ("a") [flags 0x2] <var_decl 0x7c866435d000 a>) (const_int 4 [0x4]))) [1 a+4 S1 A8])) "bf.c":11:8 86 {movqi_insn_split} (nil)) (insn 16 15 20 2 (set (reg:QI 185 [ _1+4 ]) (zero_extract:QI (reg:QI 64 [ a+4 ]) (const_int 1 [0x1]) (const_int 0 [0]))) "bf.c":11:8 985 {*extzvqi_split} (nil)) ************************************************************* After LRA: ************************************************************* (insn 587 11 13 2 (set (reg:QI 24 r24 [368]) (mem/c:QI (const:HI (plus:HI (symbol_ref:HI ("a") [flags 0x2] <var_decl 0x7c866435d000 a>) (const_int 3 [0x3]))) [1 a+3 S1 A8])) "bf.c":11:8 86 {movqi_insn_split} (nil)) (insn 13 587 15 2 (set (mem/c:QI (plus:HI (reg/f:HI 28 r28) (const_int 1 [0x1])) [4 %sfp+1 S1 A8]) (reg:QI 24 r24 [368])) "bf.c":11:8 86 {movqi_insn_split} (nil)) (insn 15 13 16 2 (set (reg:QI 6 r6 [orig:64 a+4 ] [64]) (mem/c:QI (const:HI (plus:HI (symbol_ref:HI ("a") [flags 0x2] <var_decl 0x7c866435d000 a>) (const_int 4 [0x4]))) [1 a+4 S1 A8])) "bf.c":11:8 86 {movqi_insn_split} (nil)) (insn 16 15 572 2 (set (reg:QI 24 r24 [orig:185 _1+4 ] [185]) (zero_extract:QI (reg:QI 6 r6 [orig:64 a+4 ] [64]) (const_int 1 [0x1]) (const_int 0 [0]))) "bf.c":11:8 985 {*extzvqi_split} (nil)) (insn 572 16 20 2 (set (mem/c:QI (plus:HI (reg/f:HI 28 r28) (const_int 1 [0x1])) [4 %sfp+1 S1 A8]) (reg:QI 24 r24 [orig:185 _1+4 ] [185])) "bf.c":11:8 86 {movqi_insn_split} (nil)) ************************************************************* Insn 13 and insn 572 use sfp+1 as a spill slot, but in IRA pass it was a two different pseudos r184 and r185. Insns 13 use sfp+1 as a spill slot for r184 Insns 572 use the same slot for r185. It's wrong. Here we have a rematerialization. Fragment from bf.c.317r.reload: ************************************************************************************** ******** Rematerialization #1: ******** df_worklist_dataflow_doublequeue: n_basic_blocks 14 n_edges 18 count 14 ( 1) df_worklist_dataflow_doublequeue: n_basic_blocks 14 n_edges 18 count 14 ( 1) Cands: 0 (nop=0, remat_regno=185, reload_regno=359): (insn 16 15 572 2 (set (reg:QI 359 [orig:185 _1+4 ] [185]) (zero_extract:QI (reg:QI 64 [ a+4 ]) (const_int 1 [0x1]) (const_int 0 [0]))) "bf.c":11:8 985 {*extzvqi_split} (nil)) ************************************************************************************** [...] ************************************************************************************** Ranges after the compression: r185: [0..1] Frame pointer can not be eliminated anymore Spilling non-eliminable hard regs: 28 29 Spilling r113(28) Spilling r184(29) Spilling r208(29) Spilling r209(28) Slot 0 regnos (width = 0): 185 209 208 184 113 ************************************************************************************** The bug is here: `r185: [0..1]' wrong live range after compression. r185 and r184 can't have the same spill slot ! Rematerialization in bf.c.317r.reload looks like: ************************************************************* 24: r14:QI=r185:QI Inserting rematerialization insn before: 581: r14:QI=zero_extract(r64:QI,0x1,0) deleting insn with uid = 24. Considering alt=0 of insn 16: (0) =r (1) rYil (2) n overall=0,losers=0,rld_nregs=0 32: r22:QI=r185:QI Inserting rematerialization insn before: 582: r22:QI=zero_extract(r64:QI,0x1,0) deleting insn with uid = 32. ************************************************************* It's happened because: Fragment from lra.c (lra): ************************************************************************* if (! live_p) { /* We need full live info for spilling pseudos into registers instead of memory. */ lra_create_live_ranges (lra_reg_spill_p, true); live_p = true; } /* We should check necessity for spilling here as the above live range pass can remove spilled pseudos. */ if (! lra_need_for_spills_p ()) break; /* Now we know what pseudos should be spilled. Try to rematerialize them first. */ if (lra_remat ()) { /* We need full live info -- see the comment above. */ lra_create_live_ranges (lra_reg_spill_p, true); ----------------------------------^^^^^^^^^^^^^^^ live_p = true; ************************************************************************* The bug is here. Rematerialization sometimes can be like spilling pseudos into registers. 582: r22:QI=zero_extract(r64:QI,0x1,0) So, here we need a live ranges for all pseudos. PS: the patch will not affect any target with usable definition of TARGET_SPILL_CLASS hook. PR target/116778 gcc/ * lra-lives.cc (complete_info_p): Clarification of the comment. * lra.cc (lra): Create a full live info after rematerialization.
