| Message ID | alpine.DEB.2.02.1704290907370.10028@stedding.saclay.inria.fr |
|---|---|
| State | New |
| Headers | show |
On April 29, 2017 9:17:12 AM GMT+02:00, Marc Glisse <marc.glisse@inria.fr> wrote: >Hello, > >this patch seems rather trivial, once one knows that those functions >always write exactly n characters (they fill with 0 as needed at the >end). > >Bootstrap+regtest on powerpc64le-unknown-linux-gnu. OK. Richard. >2017-05-02 Marc Glisse <marc.glisse@inria.fr> > > PR tree-optimization/80487 >gcc/ > * tree-ssa-alias.c (stmt_kills_ref_p): Handle stpncpy and strncpy. > >gcc/testsuite/ > * gcc.dg/tree-ssa/strncpy-1.c: New file.
On 04/29/2017 01:17 AM, Marc Glisse wrote: > Hello, > > this patch seems rather trivial, once one knows that those functions > always write exactly n characters (they fill with 0 as needed at the end). Nice! Now it just needs to be made to work the other way around too, so the dead str{,n}cpy calls is eliminated: void sink (void*); void f (const char *s) { char a[256]; __builtin_strncpy (a, s, sizeof a); __builtin_memset (a, 0, sizeof a); sink (a); } I've opened bug 80576 for this small improvement. Martin
On Sun, 30 Apr 2017, Martin Sebor wrote: > On 04/29/2017 01:17 AM, Marc Glisse wrote: >> Hello, >> >> this patch seems rather trivial, once one knows that those functions >> always write exactly n characters (they fill with 0 as needed at the end). > > Nice! Now it just needs to be made to work the other way around > too, so the dead str{,n}cpy calls is eliminated: I think I've seen related patches on the list, Prathamesh Kulkarni seems to be working on it.
Index: gcc/testsuite/gcc.dg/tree-ssa/strncpy-1.c =================================================================== --- gcc/testsuite/gcc.dg/tree-ssa/strncpy-1.c (nonexistent) +++ gcc/testsuite/gcc.dg/tree-ssa/strncpy-1.c (working copy) @@ -0,0 +1,16 @@ +/* { dg-do compile } */ +/* { dg-options "-O -fdump-tree-optimized" } */ + +void sink (void*); + +void f (const char *s) +{ + char a[256]; + + __builtin_memset (a, 0, sizeof a); // redundant memset + __builtin_strncpy (a, s, sizeof a); + + sink (a); +} + +/* { dg-final { scan-tree-dump-not "memset" "optimized" } } */ Index: gcc/tree-ssa-alias.c =================================================================== --- gcc/tree-ssa-alias.c (revision 247405) +++ gcc/tree-ssa-alias.c (working copy) @@ -2531,20 +2531,22 @@ stmt_kills_ref_p (gimple *stmt, ao_ref * } case BUILT_IN_MEMCPY: case BUILT_IN_MEMPCPY: case BUILT_IN_MEMMOVE: case BUILT_IN_MEMSET: case BUILT_IN_MEMCPY_CHK: case BUILT_IN_MEMPCPY_CHK: case BUILT_IN_MEMMOVE_CHK: case BUILT_IN_MEMSET_CHK: + case BUILT_IN_STRNCPY: + case BUILT_IN_STPNCPY: { /* For a must-alias check we need to be able to constrain the access properly. */ if (ref->max_size == -1) return false; tree dest = gimple_call_arg (stmt, 0); tree len = gimple_call_arg (stmt, 2); if (!tree_fits_shwi_p (len)) return false; tree rbase = ref->base;