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From: Siddhesh Poyarekar <siddhesh@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-6568] tree-optimization/104009: Conservative underflow estimate in object size Date: Fri, 14 Jan 2022 08:11:04 +0000 (GMT) [thread overview] Message-ID: <20220114081104.978383858404@sourceware.org> (raw) https://gcc.gnu.org/g:17df585a3a6a852c71883cc2ff40e111a6875149 commit r12-6568-g17df585a3a6a852c71883cc2ff40e111a6875149 Author: Siddhesh Poyarekar <siddhesh@gotplt.org> Date: Fri Jan 14 08:56:15 2022 +0530 tree-optimization/104009: Conservative underflow estimate in object size Restrict negative offset computation only to dynamic object sizes, where size expressions are accurate and not a maximum/minimum estimate and in cases where negative offsets definitely mean an underflow, e.g. in MEM_REF of the whole object with negative ofset in addr_object_size. This ends up missing some cases where __builtin_object_size could have come up with more precise results, so tests have been adjusted to reflect that. gcc/ChangeLog: PR tree-optimization/104009 * tree-object-size.c (compute_builtin_object_size): Bail out on negative offset. (plus_stmt_object_size): Return maximum of wholesize and minimum of 0 for negative offset. gcc/testsuite/ChangeLog: PR tree-optimization/104009 * gcc.dg/builtin-object-size-1.c (test10): New test. * gcc.dg/builtin-object-size-3.c (test10): Likewise. (test9): Expect zero size for negative offsets. * gcc.dg/builtin-object-size-4.c (test8): Likewise. * gcc.dg/builtin-object-size-5.c (test7): Drop test for __builtin_object_size. Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org> Diff: --- gcc/testsuite/gcc.dg/builtin-object-size-1.c | 27 ++++++++++++++++++++++ gcc/testsuite/gcc.dg/builtin-object-size-3.c | 34 ++++++++++++++++++++++++---- gcc/testsuite/gcc.dg/builtin-object-size-4.c | 6 ++--- gcc/testsuite/gcc.dg/builtin-object-size-5.c | 2 ++ gcc/tree-object-size.c | 15 ++++++++++-- 5 files changed, 75 insertions(+), 9 deletions(-) diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-1.c b/gcc/testsuite/gcc.dg/builtin-object-size-1.c index 161f426ec0b..b772e2da9b9 100644 --- a/gcc/testsuite/gcc.dg/builtin-object-size-1.c +++ b/gcc/testsuite/gcc.dg/builtin-object-size-1.c @@ -603,6 +603,32 @@ test9 (unsigned cond) #endif } +void +__attribute__ ((noinline)) +test10 (void) +{ + static char buf[255]; + unsigned int i, len = sizeof (buf); + char *p = buf; + + for (i = 0 ; i < sizeof (buf) ; i++) + { + if (len < 2) + { +#ifdef __builtin_object_size + if (__builtin_object_size (p - 3, 0) != sizeof (buf) - i + 3) + abort (); +#else + if (__builtin_object_size (p - 3, 0) != sizeof (buf)) + abort (); +#endif + break; + } + p++; + len--; + } +} + int main (void) { @@ -617,5 +643,6 @@ main (void) test7 (); test8 (); test9 (1); + test10 (); exit (0); } diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-3.c b/gcc/testsuite/gcc.dg/builtin-object-size-3.c index db31171a8bd..44a99189776 100644 --- a/gcc/testsuite/gcc.dg/builtin-object-size-3.c +++ b/gcc/testsuite/gcc.dg/builtin-object-size-3.c @@ -581,7 +581,7 @@ test9 (unsigned cond) if (__builtin_object_size (&p[-4], 2) != (cond ? 6 : 10)) abort (); #else - if (__builtin_object_size (&p[-4], 2) != 6) + if (__builtin_object_size (&p[-4], 2) != 0) abort (); #endif @@ -592,7 +592,7 @@ test9 (unsigned cond) if (__builtin_object_size (p, 2) != ((cond ? 2 : 6) + cond)) abort (); #else - if (__builtin_object_size (p, 2) != 2) + if (__builtin_object_size (p, 2) != 0) abort (); #endif @@ -605,12 +605,37 @@ test9 (unsigned cond) != sizeof (y) - __builtin_offsetof (struct A, c) - 8 + cond) abort (); #else - if (__builtin_object_size (p, 2) - != sizeof (y) - __builtin_offsetof (struct A, c) - 8) + if (__builtin_object_size (p, 2) != 0) abort (); #endif } +void +__attribute__ ((noinline)) +test10 (void) +{ + static char buf[255]; + unsigned int i, len = sizeof (buf); + char *p = buf; + + for (i = 0 ; i < sizeof (buf) ; i++) + { + if (len < 2) + { +#ifdef __builtin_object_size + if (__builtin_object_size (p - 3, 2) != sizeof (buf) - i + 3) + abort (); +#else + if (__builtin_object_size (p - 3, 2) != 0) + abort (); +#endif + break; + } + p++; + len--; + } +} + int main (void) { @@ -625,5 +650,6 @@ main (void) test7 (); test8 (); test9 (1); + test10 (); exit (0); } diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-4.c b/gcc/testsuite/gcc.dg/builtin-object-size-4.c index f644890dd14..b9fddfed036 100644 --- a/gcc/testsuite/gcc.dg/builtin-object-size-4.c +++ b/gcc/testsuite/gcc.dg/builtin-object-size-4.c @@ -489,7 +489,7 @@ test8 (unsigned cond) if (__builtin_object_size (&p[-4], 3) != (cond ? 6 : 10)) abort (); #else - if (__builtin_object_size (&p[-4], 3) != 6) + if (__builtin_object_size (&p[-4], 3) != 0) abort (); #endif @@ -500,7 +500,7 @@ test8 (unsigned cond) if (__builtin_object_size (p, 3) != ((cond ? 2 : 6) + cond)) abort (); #else - if (__builtin_object_size (p, 3) != 2) + if (__builtin_object_size (p, 3) != 0) abort (); #endif @@ -512,7 +512,7 @@ test8 (unsigned cond) if (__builtin_object_size (p, 3) != sizeof (y.c) - 8 + cond) abort (); #else - if (__builtin_object_size (p, 3) != sizeof (y.c) - 8) + if (__builtin_object_size (p, 3) != 0) abort (); #endif } diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-5.c b/gcc/testsuite/gcc.dg/builtin-object-size-5.c index cb8f753b039..d1ad761cb69 100644 --- a/gcc/testsuite/gcc.dg/builtin-object-size-5.c +++ b/gcc/testsuite/gcc.dg/builtin-object-size-5.c @@ -89,6 +89,7 @@ test6 (void) abort (); } +#ifdef __builtin_object_size void test7 (void) { @@ -97,5 +98,6 @@ test7 (void) if (__builtin_object_size (p + 2, 0) != 0) abort (); } +#endif /* { dg-final { scan-assembler-not "abort" } } */ diff --git a/gcc/tree-object-size.c b/gcc/tree-object-size.c index 3a39e6f15bb..8be0df6ba40 100644 --- a/gcc/tree-object-size.c +++ b/gcc/tree-object-size.c @@ -1054,7 +1054,8 @@ compute_builtin_object_size (tree ptr, int object_size_type, ptr = gimple_assign_rhs1 (def); if (((object_size_type & OST_DYNAMIC) - || tree_fits_shwi_p (offset)) + || (tree_fits_shwi_p (offset) + && compare_tree_int (offset, offset_limit) <= 0)) && compute_builtin_object_size (ptr, object_size_type, psize)) { @@ -1346,8 +1347,18 @@ plus_stmt_object_size (struct object_size_info *osi, tree var, gimple *stmt) /* size_for_offset doesn't make sense for -1 size, but it does for size 0 since the wholesize could be non-zero and a negative offset could give a non-zero size. */ - if (!size_unknown_p (bytes, 0)) + if (size_unknown_p (bytes, 0)) + ; + else if ((object_size_type & OST_DYNAMIC) + || compare_tree_int (op1, offset_limit) <= 0) bytes = size_for_offset (bytes, op1, wholesize); + /* In the static case, with a negative offset, the best estimate for + minimum size is size_unknown but for maximum size, the wholesize is a + better estimate than size_unknown. */ + else if (object_size_type & OST_MINIMUM) + bytes = size_unknown (object_size_type); + else + bytes = wholesize; } else bytes = wholesize = size_unknown (object_size_type);
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