On Thu, Sep 25, 2014 at 7:26 PM, Jeff Law <l...@redhat.com> wrote: > On 09/24/14 13:39, Uros Bizjak wrote: >> >> Hello! >> >> The failure was caused by barrier detection code, which failed to >> detect barrier after call insn was to be split when >> NOTE_CALL_ARG_LOCATION was present. This problem caused >> -fcompare-debug failure. >> >> Digging a bit deeped, and as hinted in the PR, the handling of >> barriers in try_split seems to be broken. The code is emitting extra >> barrier for non-debug compiles, but it "forgots" to remove the >> existing one, leading to duplicated barriers. The barrier is not >> detected at all for debug build. >> >> I have removed special handling of barriers here (also, the comment in >> removed code was not helpful at all), and this solved -fcompare-debug >> failure. >> >> The patch was also bootstrapped and regression tested on >> x86_64-linux-gnu {,-m32} which in -m32 mode splits x87 FP jump insns, >> and there were no regressions. However, I am not too familiar with >> rtl-optimization part and I am not confident that this code surgery is >> fully correct, so this is the reason for RFC status of the patch. >> >> 2014-09-24 Uros Bizjak <ubiz...@gmail.com> >> >> PR rtl-optimization/63348 >> * emit-rtl.c (try_split): Do not emit extra barrier. > > Good grief, the code you're removing pre-dates any version control we have. > ie, it's in the first revision of emit-rtl.c from 1992. Egad. > > It's going to be a hell of a time figuring out why that code exists in the > first place. I don't like removing code if we don't know why the code > exists... Any reason you picked that route rather than looking forward > through the NOTEs to see if they're followed by a suitable BARRIER?
I have tried with alternative patch that just skipped the NOTE: --cut here-- Index: emit-rtl.c =================================================================== --- emit-rtl.c (revision 215606) +++ emit-rtl.c (working copy) @@ -3622,6 +3622,10 @@ try_split (rtx pat, rtx uncast_trial, int last) int njumps = 0; rtx call_insn = NULL_RTX; + if (after && NOTE_P (after) + && NOTE_KIND (after) == NOTE_INSN_CALL_ARG_LOCATION) + after = NEXT_INSN (after); + /* We're not good at redistributing frame information. */ if (RTX_FRAME_RELATED_P (trial)) return trial; --cut here-- and resulted in: (call_insn 184 190 185 (parallel [ (call (mem:SI (reg:SI 25 $25 [217]) [0 S4 A32]) (const_int 16 [0x10])) (clobber (reg:SI 31 $31)) (clobber (reg:SI 28 $28)) ]) pr43670.c:29 595 {call_split} (expr_list:REG_NORETURN (const_int 0 [0]) (nil)) (expr_list (use (reg:SI 79 $fakec)) (expr_list (use (reg:SI 28 $28)) (nil)))) (barrier 185 184 175) (note 175 185 130 (expr_list:REG_DEP_TRUE (concat:SI (pc) (unspec:SI [ (reg:SI 28 $28) (const:SI (unspec:SI [ (symbol_ref:SI ("abort") [flags 0x41] <function_decl 0x7fe1e3af2e58 abort>) ] 227)) (reg:SI 79 $fakec) ] UNSPEC_LOAD_CALL)) (nil)) NOTE_INSN_CALL_ARG_LOCATION) (barrier 130 175 174) I have noticed that the barrier is always there, since without -g, we have: (call_insn 76 82 77 (parallel [ (call (mem:SI (reg:SI 25 $25 [217]) [0 S4 A32]) (const_int 16 [0x10])) (clobber (reg:SI 31 $31)) (clobber (reg:SI 28 $28)) ]) pr43670.c:29 595 {call_split} (expr_list:REG_NORETURN (const_int 0 [0]) (nil)) (expr_list (use (reg:SI 79 $fakec)) (expr_list (use (reg:SI 28 $28)) (nil)))) (barrier 77 76 37) (barrier 37 77 40) and considering the fact that the code didn't process barriers correctly with -g, I simply removed the emission. The - probably stalled - comment was not helpful at all. Uros.