From 623c6fddd605f8f225142d714440320e4ef54d84 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Wed, 15 Jan 2020 01:28:43 +0100 Subject: [PATCH] tree-optimization: Fix tree dse of strncpy PR93249 As the testcase shows, tail trimming of strncpy in tree-ssa-dse.c is fine, we just copy or clear fewer bytes in the destination, but unlike memcpy/memset etc., head trimming is problematic in certain cases. If we can prove that there are no zero bytes among initial head_trim bytes, it is ok to trim it, if we can prove there is at least one zero byte among initial head_trim bytes, we could (not implemented in the patch) turn the strncpy into memset 0, but otherwise we need to avoid the head trimming, because the presence or absence of NUL byte there changes the behavior for subsequent bytes, whether further bytes from src are copied or if further bytes are cleared. 2020-01-15 Jakub Jelinek PR tree-optimization/93249 * tree-ssa-dse.c: Include builtins.h and gimple-fold.h. (maybe_trim_memstar_call): Move head_trim and tail_trim vars to function body scope, reindent. For BUILTIN_IN_STRNCPY*, don't perform head trim unless we can prove there are no '\0' chars from the source among the first head_trim chars. * gcc.c-torture/execute/pr93249.c: New test. --- gcc/ChangeLog | 9 ++ gcc/testsuite/ChangeLog | 5 + gcc/testsuite/gcc.c-torture/execute/pr93249.c | 40 +++++++ gcc/tree-ssa-dse.c | 109 +++++++++++------- 4 files changed, 123 insertions(+), 40 deletions(-) create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr93249.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 73170037f0d..8f4382030b9 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,12 @@ +2020-01-15 Jakub Jelinek + + PR tree-optimization/93249 + * tree-ssa-dse.c: Include builtins.h and gimple-fold.h. + (maybe_trim_memstar_call): Move head_trim and tail_trim vars to + function body scope, reindent. For BUILTIN_IN_STRNCPY*, don't + perform head trim unless we can prove there are no '\0' chars + from the source among the first head_trim chars. + 2020-01-14 David Malcolm * Makefile.in (ANALYZER_OBJS): Add analyzer/function-set.o. diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 8013bdbc2eb..77d573fed28 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2020-01-15 Jakub Jelinek + + PR tree-optimization/93249 + * gcc.c-torture/execute/pr93249.c: New test. + 2020-01-14 David Malcolm * gcc.dg/analyzer/signal-5.c: New test. diff --git a/gcc/testsuite/gcc.c-torture/execute/pr93249.c b/gcc/testsuite/gcc.c-torture/execute/pr93249.c new file mode 100644 index 00000000000..2c9a6b4dee0 --- /dev/null +++ b/gcc/testsuite/gcc.c-torture/execute/pr93249.c @@ -0,0 +1,40 @@ +/* PR tree-optimization/93249 */ + +char a[2], b[4], c[6]; + +void +foo (void) +{ + char d[2] = { 0x00, 0x11 }; + __builtin_strncpy (&b[2], d, 2); + __builtin_strncpy (&b[1], a, 2); + if (b[0] || b[1] || b[2] || b[3]) + __builtin_abort (); +} + +void +bar (void) +{ + __builtin_strncpy (&b[2], "\0\x11", 2); + __builtin_strncpy (&b[1], a, 2); + if (b[0] || b[1] || b[2] || b[3]) + __builtin_abort (); +} + +void +baz (void) +{ + __builtin_strncpy (&c[2], "\x11\x11\0\x11", 4); + __builtin_strncpy (&c[1], a, 2); + if (c[0] || c[1] || c[2] || c[3] != 0x11 || c[4] || c[5]) + __builtin_abort (); +} + +int +main () +{ + foo (); + bar (); + baz (); + return 0; +} diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c index b0120d4e74d..cb64d6fe83a 100644 --- a/gcc/tree-ssa-dse.c +++ b/gcc/tree-ssa-dse.c @@ -36,6 +36,8 @@ along with GCC; see the file COPYING3. If not see #include "alias.h" #include "tree-ssa-loop.h" #include "tree-ssa-dse.h" +#include "builtins.h" +#include "gimple-fold.h" /* This file implements dead store elimination. @@ -456,56 +458,83 @@ increment_start_addr (gimple *stmt, tree *where, int increment) static void maybe_trim_memstar_call (ao_ref *ref, sbitmap live, gimple *stmt) { + int head_trim, tail_trim; switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt))) { + case BUILT_IN_STRNCPY: + case BUILT_IN_STRNCPY_CHK: + compute_trims (ref, live, &head_trim, &tail_trim, stmt); + if (head_trim) + { + /* Head trimming of strncpy is only possible if we can + prove all bytes we would trim are non-zero (or we could + turn the strncpy into memset if there must be zero + among the head trimmed bytes). If we don't know anything + about those bytes, the presence or absence of '\0' bytes + in there will affect whether it acts for the non-trimmed + bytes as memset or memcpy/strncpy. */ + c_strlen_data lendata = { }; + int orig_head_trim = head_trim; + tree srcstr = gimple_call_arg (stmt, 1); + if (!get_range_strlen (srcstr, &lendata, /*eltsize=*/1) + || !tree_fits_uhwi_p (lendata.minlen)) + head_trim = 0; + else if (tree_to_uhwi (lendata.minlen) < (unsigned) head_trim) + { + head_trim = tree_to_uhwi (lendata.minlen); + if ((orig_head_trim & (UNITS_PER_WORD - 1)) == 0) + head_trim &= ~(UNITS_PER_WORD - 1); + } + if (orig_head_trim != head_trim + && dump_file + && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + " Adjusting strncpy trimming to (head = %d," + " tail = %d)\n", head_trim, tail_trim); + } + goto do_memcpy; + case BUILT_IN_MEMCPY: case BUILT_IN_MEMMOVE: - case BUILT_IN_STRNCPY: case BUILT_IN_MEMCPY_CHK: case BUILT_IN_MEMMOVE_CHK: - case BUILT_IN_STRNCPY_CHK: - { - int head_trim, tail_trim; - compute_trims (ref, live, &head_trim, &tail_trim, stmt); - - /* Tail trimming is easy, we can just reduce the count. */ - if (tail_trim) - decrement_count (stmt, tail_trim); - - /* Head trimming requires adjusting all the arguments. */ - if (head_trim) - { - tree *dst = gimple_call_arg_ptr (stmt, 0); - increment_start_addr (stmt, dst, head_trim); - tree *src = gimple_call_arg_ptr (stmt, 1); - increment_start_addr (stmt, src, head_trim); - decrement_count (stmt, head_trim); - } - break; - } + compute_trims (ref, live, &head_trim, &tail_trim, stmt); + + do_memcpy: + /* Tail trimming is easy, we can just reduce the count. */ + if (tail_trim) + decrement_count (stmt, tail_trim); + + /* Head trimming requires adjusting all the arguments. */ + if (head_trim) + { + tree *dst = gimple_call_arg_ptr (stmt, 0); + increment_start_addr (stmt, dst, head_trim); + tree *src = gimple_call_arg_ptr (stmt, 1); + increment_start_addr (stmt, src, head_trim); + decrement_count (stmt, head_trim); + } + break; case BUILT_IN_MEMSET: case BUILT_IN_MEMSET_CHK: - { - int head_trim, tail_trim; - compute_trims (ref, live, &head_trim, &tail_trim, stmt); - - /* Tail trimming is easy, we can just reduce the count. */ - if (tail_trim) - decrement_count (stmt, tail_trim); - - /* Head trimming requires adjusting all the arguments. */ - if (head_trim) - { - tree *dst = gimple_call_arg_ptr (stmt, 0); - increment_start_addr (stmt, dst, head_trim); - decrement_count (stmt, head_trim); - } - break; - } + compute_trims (ref, live, &head_trim, &tail_trim, stmt); + + /* Tail trimming is easy, we can just reduce the count. */ + if (tail_trim) + decrement_count (stmt, tail_trim); + + /* Head trimming requires adjusting all the arguments. */ + if (head_trim) + { + tree *dst = gimple_call_arg_ptr (stmt, 0); + increment_start_addr (stmt, dst, head_trim); + decrement_count (stmt, head_trim); + } + break; - default: - break; + default: + break; } } -- 2.30.2