https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113613
Alex Coplan <acoplan at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |rsandifo at gcc dot gnu.org Summary|[14 Regression] Missing |[14 Regression] Missing |ldp/stp optimization |ldp/stp optimization since |sometimes |r14-6290-g9f0f7d802482a8 --- Comment #4 from Alex Coplan <acoplan at gcc dot gnu.org> --- Interestingly we started to miss this with the introduction of aarch64 early RA i.e. r14-6290-g9f0f7d802482a8958d6cdc72f1fe0c8549db2182. My ldp/stp pattern rewrite was: r14-6604-gd7ee988c491cde43d04fe25f2b3dbad9d85ded45 so we started to miss this before any of my ldp/stp patches. Looking at what happens with the ldp/stp pass, I can see that in sched1 we've already allocated hard regs to the vector load destinations: 3: NOTE_INSN_BASIC_BLOCK 2 2: NOTE_INSN_FUNCTION_BEG 13: NOTE_INSN_DELETED 5: debug begin stmt marker 6: r107:DI=high(`*.LANCHOR0') 7: r106:DI=r107:DI+low(`*.LANCHOR0') REG_EQUAL `*.LANCHOR0' 14: v31:V2SF=[r107:DI+low(`*.LANCHOR0')] 15: v30:V2SF=[r106:DI+0x20] 16: v30:V2SF=v31:V2SF+v30:V2SF REG_DEAD v31:V2SF 27: v31:V2SF=[r106:DI+0x8] 17: [r107:DI+low(`*.LANCHOR0')]=v30:V2SF REG_DEAD r107:DI REG_DEAD v30:V2SF 18: debug begin stmt marker 28: v30:V2SF=[r106:DI+0x28] 29: v30:V2SF=v31:V2SF+v30:V2SF REG_DEAD v31:V2SF 30: [r106:DI+0x8]=v30:V2SF REG_DEAD r106:DI REG_DEAD v30:V2SF 33: NOTE_INSN_DELETED and then there's nothing that the early ldp/stp pass can do because the would-be load pair candidates already use the same (hard) transfer register due to early RA: merge_pairs [L=1], cand vecs (14) x (27) analyzing pair (load=1): (14,27) punting on ldp due to reg conflcits (14,27) merge_pairs [L=1], cand vecs (15) x (28) analyzing pair (load=1): (15,28) punting on ldp due to reg conflcits (15,28) merge_pairs [L=0], cand vecs (17) x (30) analyzing pair (load=0): (17,30) pair (17,30): rejecting base 106 due to dataflow hazards (28,29) can't form pair (17,30) due to dataflow hazards starting the processing of deferred insns ending the processing of deferred insns CCing Richard S for an opinion.