| Message ID | 530F8BC9.1020505@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Thu, Feb 27, 2014 at 11:02 AM, Jeff Law <law@redhat.com> wrote: > > As discussed in 49847, a few years ago GCC was changed to add EH edges for > exceptions that might arise from a floating point comparison. That change > made it possible for a cc0-setter and cc0-user to end up in different > blocks, separated by a NOTE. > > After discussing reverting the change, duplicating the cc0-setter and a > couple other ideas, eventually Richi and myself settled on relaxing the long > standing restrictions on the relative locations of the cc0 setter and cc0 > user. > > We agreed to update the documentation and fault in fixes due to low priority > of cc0 targets (and doubly so since this really only affects cc0 targets > with used with non-call-exceptions). > > This patch updates the documentation and fixes the only known failure due to > this change in cse.c with a patch from Mikael. > > Tested with a cross compiler. I'll probably fire off a m68k bootstrap for > good measure, but it'll be several days before that completes. > > Installed on the trunk. > > Jeff > > diff --git a/gcc/ChangeLog b/gcc/ChangeLog > index 8a78716..a20cee3 100644 > --- a/gcc/ChangeLog > +++ b/gcc/ChangeLog > @@ -1,3 +1,12 @@ > +2014-02-27 Mikael Pettersson <mikpe@it.uu.se> > + Jeff Law <law@redhat.com> > + > + PR rtl-optimization/49847 > + * cse.c (fold_rtx) Handle case where cc0 setter and cc0 user > + are in different blocks. > + * doc/tm.texi (Condition Code Status): Update documention for > + relative locations of cc0-setter and cc0-user. > + This breaks bootstrap: You should edit ../../src-trunk/gcc/doc/tm.texi.in rather than ../../src-trunk/gcc/doc/tm.texi . make[6]: *** [s-tm-texi] Error 1 make[6]: *** Waiting for unfinished jobs....
On 02/27/14 12:50, H.J. Lu wrote: > On Thu, Feb 27, 2014 at 11:02 AM, Jeff Law <law@redhat.com> wrote: >> >> As discussed in 49847, a few years ago GCC was changed to add EH edges for >> exceptions that might arise from a floating point comparison. That change >> made it possible for a cc0-setter and cc0-user to end up in different >> blocks, separated by a NOTE. >> >> After discussing reverting the change, duplicating the cc0-setter and a >> couple other ideas, eventually Richi and myself settled on relaxing the long >> standing restrictions on the relative locations of the cc0 setter and cc0 >> user. >> >> We agreed to update the documentation and fault in fixes due to low priority >> of cc0 targets (and doubly so since this really only affects cc0 targets >> with used with non-call-exceptions). >> >> This patch updates the documentation and fixes the only known failure due to >> this change in cse.c with a patch from Mikael. >> >> Tested with a cross compiler. I'll probably fire off a m68k bootstrap for >> good measure, but it'll be several days before that completes. >> >> Installed on the trunk. >> >> Jeff >> >> diff --git a/gcc/ChangeLog b/gcc/ChangeLog >> index 8a78716..a20cee3 100644 >> --- a/gcc/ChangeLog >> +++ b/gcc/ChangeLog >> @@ -1,3 +1,12 @@ >> +2014-02-27 Mikael Pettersson <mikpe@it.uu.se> >> + Jeff Law <law@redhat.com> >> + >> + PR rtl-optimization/49847 >> + * cse.c (fold_rtx) Handle case where cc0 setter and cc0 user >> + are in different blocks. >> + * doc/tm.texi (Condition Code Status): Update documention for >> + relative locations of cc0-setter and cc0-user. >> + > > This breaks bootstrap: > > You should edit ../../src-trunk/gcc/doc/tm.texi.in rather than > ../../src-trunk/gcc/doc/tm.texi . > make[6]: *** [s-tm-texi] Error 1 > make[6]: *** Waiting for unfinished jobs.... Nuts. Sorry. Thanks for fixing it. jeff
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 8a78716..a20cee3 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,12 @@ +2014-02-27 Mikael Pettersson <mikpe@it.uu.se> + Jeff Law <law@redhat.com> + + PR rtl-optimization/49847 + * cse.c (fold_rtx) Handle case where cc0 setter and cc0 user + are in different blocks. + * doc/tm.texi (Condition Code Status): Update documention for + relative locations of cc0-setter and cc0-user. + 2014-02-27 Vladimir Makarov <vmakarov@redhat.com> PR target/59222 diff --git a/gcc/cse.c b/gcc/cse.c index cffa553..dba85f1 100644 --- a/gcc/cse.c +++ b/gcc/cse.c @@ -3199,9 +3199,27 @@ fold_rtx (rtx x, rtx insn) #ifdef HAVE_cc0 case CC0: - folded_arg = prev_insn_cc0; - mode_arg = prev_insn_cc0_mode; - const_arg = equiv_constant (folded_arg); + /* The cc0-user and cc0-setter may be in different blocks if + the cc0-setter potentially traps. In that case PREV_INSN_CC0 + will have been cleared as we exited the block with the + setter. + + While we could potentially track cc0 in this case, it just + doesn't seem to be worth it given that cc0 targets are not + terribly common or important these days and trapping math + is rarely used. The combination of those two conditions + necessary to trip this situation is exceedingly rare in the + real world. */ + if (!prev_insn_cc0) + { + const_arg = NULL_RTX; + } + else + { + folded_arg = prev_insn_cc0; + mode_arg = prev_insn_cc0_mode; + const_arg = equiv_constant (folded_arg); + } break; #endif diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index f204936..f7024a7 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -5900,8 +5900,13 @@ most instructions do not affect it. The latter category includes most RISC machines. The implicit clobbering poses a strong restriction on the placement of -the definition and use of the condition code, which need to be in adjacent -insns for machines using @code{(cc0)}. This can prevent important +the definition and use of the condition code. In the past the definition +and use were always adjacent. However, recent changes to support trapping +arithmatic may result in the definition and user being in different blocks. +Thus, there may be a @code{NOTE_INSN_BASIC_BLOCK} between them. Additionally, +the definition may be the source of exception handling edges. + +These restrictions can prevent important optimizations on some machines. For example, on the IBM RS/6000, there is a delay for taken branches unless the condition code register is set three instructions earlier than the conditional branch. The instruction diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 128a5f7..be4cb12 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,9 @@ +2014-02-27 Mikael Pettersson <mikpe@it.uu.se> + Jeff Law <law@redhat.com> + + PR rtl-optimization/49847 + * g++.dg/pr49847.C: New test. + 2014-02-27 Marek Polacek <polacek@redhat.com> PR middle-end/59223 diff --git a/gcc/testsuite/g++.dg/pr49847.C b/gcc/testsuite/g++.dg/pr49847.C new file mode 100644 index 0000000..b047713 --- /dev/null +++ b/gcc/testsuite/g++.dg/pr49847.C @@ -0,0 +1,7 @@ +/* { dg-do compile } */ +/* { dg-options "-O -fnon-call-exceptions" } */ +int f (float g) +{ + try { return g >= 0; } + catch (...) {} +}