| Message ID | CAMqJFCpZqU=7Hf0q6vL-pLExZXdk8r+m5Wfwit5-Nu2L2WDN8w@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Nov 08, 2013 at 05:11:39PM +0000, Joern Rennecke wrote: > On 8 November 2013 15:50, Steven Bosscher <stevenb.gcc@gmail.com> wrote: > > Even with the gimple opts disabled, a const-const comparison would > > normally be folded by the RTL expanders. > > Well, in this spirit, attached is another way to address the RTL side > of the problem. > As mention in the PR, the tree side of the problem started showing up > in r204194. > 2013-11-08 Joern Rennecke <joern.rennecke@embecosm.com> > > PR middle-end/59049 > * expmed.c (emit_store_flag): Fail for const-const comparison. LGTM (I'd just write return NULL_RTX; instead of return 0;). > --- expmed.c (revision 204568) > +++ expmed.c (working copy) > @@ -5401,6 +5401,13 @@ emit_store_flag (rtx target, enum rtx_co > rtx subtarget; > rtx tem, last, trueval; > > + /* If we compare constants, we shouldn't use a store-flag operation, > + but a constant load. We can get there via the vanilla route that > + usually generates a compare-branch sequence, but will in this case > + fold the comparison to a constant, and thus elide the branch. */ > + if (CONSTANT_P (op0) && CONSTANT_P (op1)) > + return 0; > + > tem = emit_store_flag_1 (target, code, op0, op1, mode, unsignedp, normalizep, > target_mode); > if (tem) Jakub
Index: expmed.c =================================================================== --- expmed.c (revision 204568) +++ expmed.c (working copy) @@ -5401,6 +5401,13 @@ emit_store_flag (rtx target, enum rtx_co rtx subtarget; rtx tem, last, trueval; + /* If we compare constants, we shouldn't use a store-flag operation, + but a constant load. We can get there via the vanilla route that + usually generates a compare-branch sequence, but will in this case + fold the comparison to a constant, and thus elide the branch. */ + if (CONSTANT_P (op0) && CONSTANT_P (op1)) + return 0; + tem = emit_store_flag_1 (target, code, op0, op1, mode, unsignedp, normalizep, target_mode); if (tem)