| Message ID | 20101228210918.GR16156@tyan-ft48-01.lab.bos.redhat.com |
|---|---|
| State | New |
| Headers | show |
On Dec 28, 2010, at 4:09 PM, Jakub Jelinek wrote: > On Tue, Dec 28, 2010 at 04:03:28PM -0500, Paul Koning wrote: >> >> On Dec 28, 2010, at 3:41 PM, Richard Guenther wrote: >> >>> On Tue, Dec 28, 2010 at 8:27 PM, Paul Koning <paul_koning@dell.com> wrote: >>>> I ran into an oddity with one of the testcases. >>>> >>>> The one that scans the tree dump (gcc.dg/pr46909.c) fails for pdp11 because the tree dump file says it's checking for != 6 (which should be != 4). But the generated code is correct. >>>> >>>> Also curious is that the tree dump looks very different from the tree dump generated by the same rev compiler (give or take a few hours) on linux-x86. Any idea what's going on here? >>> >>> dependent on BRANCH_COST &&s and ||s will be lowered to control flow >>> or and/ors. You don't provide source to make the point about the >>> !=6 vs !=4 issue. >> >> The program being compiled is gcc/testsuite/gcc.dg/pr46909.c. BRANCH_COST is constant 0 on the pdp11 target. > > If ifcombine optimizes the testcase into != 6 instead of != 4, then > you are looking at what was happening before the fix. That's what I thought too. But I'm definitely using the fixed compiler. It's freshly built from a sandbox updated today, and in any case the generated code shows the correct check (a compare with 4, not a compare with 6). I went back and did some more checking. It turns out that, on pdp11, it makes no difference whether the fix is in or not; it generates correct code either way, and it produces the tree dump file that I mentioned (which looks drastically different from the linux-x86 treedump). I just did another fresh configure/build to make sure I didn't have a mixed-up build -- no, it was clean. paul
--- pr46909.c.070t.ifcombine 2010-12-28 22:06:31.000000000 +0100 +++ pr46909.c.070t.ifcombine 2010-12-28 22:06:40.000000000 +0100 @@ -1,7 +1,7 @@ ;; Function foo (foo) -optimizing two comparisons to x_2(D) != 6 +optimizing two comparisons to x_2(D) != 4 Merging blocks 2 and 3 foo (unsigned int x) { @@ -20,7 +20,7 @@ foo (unsigned int x) D.2691_6 = x_2(D) == 2; D.2692_7 = x_2(D) == 6; D.2693_8 = D.2691_6 | D.2692_7; - if (x_2(D) != 6) + if (x_2(D) != 4) goto <bb 4>; else goto <bb 3>;