Submitter | Alexandre Oliva |
---|---|

Date | Jan. 16, 2013, 4:29 a.m. |

Message ID | <orlibt6995.fsf_-_@livre.localdomain> |

Download | mbox | patch |

Permalink | /patch/212387/ |

State | New |

Headers | show |

## Comments

On Wed, Jan 16, 2013 at 5:29 AM, Alexandre Oliva <aoliva@redhat.com> wrote: >> On 01/15/2013 08:24 AM, Aldy Hernandez wrote: >>> Ok, it's really an alias.c bug, but it is Alpha, and aoliva has already >>> provided an unreviewed patch... > >>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55547 > >> The patch in #C4 is ok. > > Thanks, I'm checking it in (first patch below), but reviewing the logic > that uses negative sizes, I found a number of places that should use the > absolute value, and others in which being conservative about negative > sizes is unnecessary (e.g., when dealing with CONST_INT addresses). > That was implemented and regstrapped on x86_64-linux-gnu. Uros, would > you give the second patch a spin on alpha to make sure it doesn't > regress? Ok to install it? Thanks, I started a bootstrap/regtest run. If everything goes as expected, the results will be available in ~10h from now... Uros.

On Wed, Jan 16, 2013 at 8:33 AM, Uros Bizjak <ubizjak@gmail.com> wrote: >>> On 01/15/2013 08:24 AM, Aldy Hernandez wrote: >>>> Ok, it's really an alias.c bug, but it is Alpha, and aoliva has already >>>> provided an unreviewed patch... >> >>>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55547 >> >>> The patch in #C4 is ok. >> >> Thanks, I'm checking it in (first patch below), but reviewing the logic >> that uses negative sizes, I found a number of places that should use the >> absolute value, and others in which being conservative about negative >> sizes is unnecessary (e.g., when dealing with CONST_INT addresses). >> That was implemented and regstrapped on x86_64-linux-gnu. Uros, would >> you give the second patch a spin on alpha to make sure it doesn't >> regress? Ok to install it? > > Thanks, I started a bootstrap/regtest run. If everything goes as > expected, the results will be available in ~10h from now... The results looks good [1], no regressions with patch. [1] http://gcc.gnu.org/ml/gcc-testresults/2013-01/msg01706.html Uros.

On 01/15/2013 08:29 PM, Alexandre Oliva wrote: > if (rtx_equal_for_memref_p (x, y)) > { > - if (xsize <= 0 || ysize <= 0) > + if (xsize == 0 || ysize == 0) > return 1; > - if (c >= 0 && xsize > c) > + if (c >= 0 && abs (xsize) - c > 0) > return 1; > - if (c < 0 && ysize+c > 0) > + if (c < 0 && abs (ysize) + c > 0) > return 1; > return 0; > } > @@ -2063,7 +2063,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) > y0 = canon_rtx (XEXP (y, 0)); > if (rtx_equal_for_memref_p (x0, y0)) > return (xsize == 0 || ysize == 0 > - || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); > + || (c >= 0 && abs (xsize) - c > 0) > + || (c < 0 && abs (ysize) + c > 0)); > > /* Can't properly adjust our sizes. */ > if (!CONST_INT_P (x1)) > @@ -2119,8 +2120,9 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) > if (CONST_INT_P (x) && CONST_INT_P (y)) > { > c += (INTVAL (y) - INTVAL (x)); > - return (xsize <= 0 || ysize <= 0 > - || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); > + return (xsize == 0 || ysize == 0 > + || (c >= 0 && abs (xsize) - c > 0) > + || (c < 0 && abs (ysize) + c > 0)); > } I notice that these expressions (including the first hunk that uses ifs) are now all the same. It would seem extremely prudent to pull this out to a function so that they stay the same. That said, I question the change of <= to == 0. If negative, we don't know how much overlap there is as far as I can see. > > if (GET_CODE (x) == CONST) > @@ -2139,7 +2141,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) > if (CONSTANT_P (y)) > return (xsize <= 0 || ysize <= 0 > || (rtx_equal_for_memref_p (x, y) > - && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)))); > + && ((c >= 0 && abs (xsize) - c > 0) > + || (c < 0 && abs (ysize) + c > 0)))); This hunk is not needed, as we begin by eliminating <= 0. So the abs is certain to do nothing. r~

On Jan 16, 2013, Richard Henderson <rth@redhat.com> wrote: > I notice that these expressions (including the first hunk that uses > ifs) are now all the same. *nod* > It would seem extremely prudent to pull > this out to a function so that they stay the same. ack, will do. > That said, I question the change of <= to == 0. If negative, we don't > know how much overlap there is as far as I can see. Why not? Since the addresses are constants, and the negative sizes are just the adjusted sizes, negated to indicate they were conservatively lengthened by an alignment operation, we can determine that two references don't overlap if they're far enough from each other that, even with the alignment adjustment, they're still clearly non-overlapping. Say, if x is 0x0fff and y is 0x1234, both originally referenced with size 8 and x aligned to 0x20, it is obvious that the accesses won't overlap, in spite of the alignment on x. The test applied on constant addresses wouldn't realize that and would say they could overlap, because any alignment-adjusted size would be mistaken as “overlaps with anything”. >> if (GET_CODE (x) == CONST) >> @@ -2139,7 +2141,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) >> if (CONSTANT_P (y)) >> return (xsize <= 0 || ysize <= 0 >> || (rtx_equal_for_memref_p (x, y) >> - && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)))); >> + && ((c >= 0 && abs (xsize) - c > 0) >> + || (c < 0 && abs (ysize) + c > 0)))); > This hunk is not needed, as we begin by eliminating <= 0. So the abs > is certain to do nothing. The function I'll introduce to keep the expressions the same will have the abs and I'll use it here, but you're right that after testing for negative sizes they abses won't make much of a difference.

On 2013-01-16 18:40, Alexandre Oliva wrote: >> That said, I question the change of <= to == 0. If negative, we don't >> know how much overlap there is as far as I can see. > > Why not? Since the addresses are constants, and the negative sizes are > just the adjusted sizes, negated to indicate they were conservatively > lengthened by an alignment operation... Oh, right. >> This hunk is not needed, as we begin by eliminating <= 0. So the abs >> is certain to do nothing. > > The function I'll introduce to keep the expressions the same will have > the abs and I'll use it here, but you're right that after testing for > negative sizes they abses won't make much of a difference. Sure. r~

On Jan 16, 2013, Uros Bizjak <ubizjak@gmail.com> wrote: >> Thanks, I started a bootstrap/regtest run. If everything goes as >> expected, the results will be available in ~10h from now... > The results looks good [1], no regressions with patch. > [1] http://gcc.gnu.org/ml/gcc-testresults/2013-01/msg01706.html Thanks, the (cosmetically) revised patch is now in.

## Patch

Be conservative about negative sizes on symbols, use abs elsewhere From: Alexandre Oliva <aoliva@redhat.com> for gcc/ChangeLog PR rtl-optimization/55547 PR rtl-optimization/53827 PR debug/53671 PR debug/49888 * alias.c (memrefs_conflict_p): Use abs of sizes all over, retaining the conservative special case for symbolic constants. --- gcc/alias.c | 21 ++++++++++++--------- 1 files changed, 12 insertions(+), 9 deletions(-) diff --git a/gcc/alias.c b/gcc/alias.c index 9a386dd..d51ba09 100644 --- a/gcc/alias.c +++ b/gcc/alias.c @@ -1976,21 +1976,21 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) else if (GET_CODE (x) == LO_SUM) x = XEXP (x, 1); else - x = addr_side_effect_eval (x, xsize, 0); + x = addr_side_effect_eval (x, abs (xsize), 0); if (GET_CODE (y) == HIGH) y = XEXP (y, 0); else if (GET_CODE (y) == LO_SUM) y = XEXP (y, 1); else - y = addr_side_effect_eval (y, ysize, 0); + y = addr_side_effect_eval (y, abs (ysize), 0); if (rtx_equal_for_memref_p (x, y)) { - if (xsize <= 0 || ysize <= 0) + if (xsize == 0 || ysize == 0) return 1; - if (c >= 0 && xsize > c) + if (c >= 0 && abs (xsize) - c > 0) return 1; - if (c < 0 && ysize+c > 0) + if (c < 0 && abs (ysize) + c > 0) return 1; return 0; } @@ -2063,7 +2063,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) y0 = canon_rtx (XEXP (y, 0)); if (rtx_equal_for_memref_p (x0, y0)) return (xsize == 0 || ysize == 0 - || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); + || (c >= 0 && abs (xsize) - c > 0) + || (c < 0 && abs (ysize) + c > 0)); /* Can't properly adjust our sizes. */ if (!CONST_INT_P (x1)) @@ -2119,8 +2120,9 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) if (CONST_INT_P (x) && CONST_INT_P (y)) { c += (INTVAL (y) - INTVAL (x)); - return (xsize <= 0 || ysize <= 0 - || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); + return (xsize == 0 || ysize == 0 + || (c >= 0 && abs (xsize) - c > 0) + || (c < 0 && abs (ysize) + c > 0)); } if (GET_CODE (x) == CONST) @@ -2139,7 +2141,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c) if (CONSTANT_P (y)) return (xsize <= 0 || ysize <= 0 || (rtx_equal_for_memref_p (x, y) - && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)))); + && ((c >= 0 && abs (xsize) - c > 0) + || (c < 0 && abs (ysize) + c > 0)))); return -1; }