Andrew Pinski <quic_apin...@quicinc.com> writes: > Late_combine exposed this latent bug in split_live_ranges_for_shrink_wrap. > What it did was copy-prop regno 151 from regno 119 from: > ``` > (insn 2 264 3 2 (set (reg/f:DI 119 [ thisD.3697 ]) > (reg:DI 151)) "/app/example.cpp":19:13 70 {*movdi_aarch64} > (expr_list:REG_DEAD (reg:DI 151) > (nil))) > ``` > > into these insns: > ``` > (debug_insn 147 146 148 5 (var_location:DI thisD.3727 (reg/f:DI 119 [ > thisD.3697 ])) "/app/example.cpp":21:5 -1 > (nil)) > .... > (insn 167 166 168 7 (set (reg:DI 1 x1) > (reg/f:DI 119 [ thisD.3697 ])) "/app/example.cpp":14:21 70 > {*movdi_aarch64} > (nil)) > ``` > > Both are valid things to do. The problem is split_live_ranges_for_shrink_wrap > looks at the > uses of reg 151 and with and without debugging reg 151 have a different usage > in different BBs. > The function is trying to find a splitting point for reg 151 and they are > different. In the end > this causes register allocation difference. > The fix is for split_live_ranges_for_shrink_wrap to ignore uses that were in > debug insns. > > Bootstrappped and tested on x86_64-linux-gnu with no regressions. > > PR rtl-optimization/116179 > > gcc/ChangeLog: > > * ira.cc (split_live_ranges_for_shrink_wrap): For the uses loop, > only look at non-debug insns. > > gcc/testsuite/ChangeLog: > > * g++.dg/torture/pr116179-1.C: New test. > > Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com> > --- > gcc/ira.cc | 4 +++- > gcc/testsuite/g++.dg/torture/pr116179-1.C | 26 +++++++++++++++++++++++ > 2 files changed, 29 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/g++.dg/torture/pr116179-1.C > > diff --git a/gcc/ira.cc b/gcc/ira.cc > index 5642aea3caa..5a04231f7bd 100644 > --- a/gcc/ira.cc > +++ b/gcc/ira.cc > @@ -5144,7 +5144,9 @@ split_live_ranges_for_shrink_wrap (void) > use = DF_REF_NEXT_REG (use)) > { > int ubbi = DF_REF_BB (use)->index; > - if (bitmap_bit_p (reachable, ubbi)) > + /* Only non debug insn should not be taken into account. */
Nit: maybe /* Only non-debug insns should be ignored. */ to remove the double negative or /* Don't ignore non-debug insns. */. (Not sure if I've confused myself with the negatives there) > + if (NONDEBUG_INSN_P (DF_REF_INSN (use)) > + && bitmap_bit_p (reachable, ubbi)) > bitmap_set_bit (need_new, ubbi); > } > last_interesting_insn = insn; > [...] thanks, sam