In r278621 I accidentally removed a test that prevented an optimization from taking place when it wasn't supposed to, causing test failures in Jeff's mass rebuilds of downstream packages (e.g., snapd). In r278742 I committed the attached patch, restoring the test.
Martin
PR tree-optimization/92683 - strncmp incorrect result with equal substrings and non-const bound gcc/testsuite/ChangeLog: PR tree-optimization/92683 * gcc.dg/strcmpopt_8.c: New test. * gcc.dg/strcmpopt_9.c: New test. gcc/ChangeLog: PR tree-optimization/92683 * gimple-fold.c (gimple_fold_builtin_string_compare): Restore a test inadvertently removed in a previous change. Rename local variable for clarity. Index: gcc/gimple-fold.c =================================================================== --- gcc/gimple-fold.c (revision 278733) +++ gcc/gimple-fold.c (working copy) @@ -2346,15 +2346,16 @@ gimple_fold_builtin_string_compare (gimple_stmt_it tree str1 = gimple_call_arg (stmt, 0); tree str2 = gimple_call_arg (stmt, 1); tree lhs = gimple_call_lhs (stmt); - tree len = NULL_TREE; + + tree bound_node = NULL_TREE; unsigned HOST_WIDE_INT bound = HOST_WIDE_INT_M1U; /* Handle strncmp and strncasecmp functions. */ if (gimple_call_num_args (stmt) == 3) { - len = gimple_call_arg (stmt, 2); - if (tree_fits_uhwi_p (len)) - bound = tree_to_uhwi (len); + bound_node = gimple_call_arg (stmt, 2); + if (tree_fits_uhwi_p (bound_node)) + bound = tree_to_uhwi (bound_node); } /* If the LEN parameter is zero, return zero. */ @@ -2418,6 +2419,9 @@ gimple_fold_builtin_string_compare (gimple_stmt_it case BUILT_IN_STRNCMP: case BUILT_IN_STRNCMP_EQ: { + if (bound == HOST_WIDE_INT_M1U) + break; + /* Reduce the bound to be no more than the length of the shorter of the two strings, or the sizes of the unterminated arrays. */ Index: gcc/testsuite/gcc.dg/strcmpopt_8.c =================================================================== --- gcc/testsuite/gcc.dg/strcmpopt_8.c (nonexistent) +++ gcc/testsuite/gcc.dg/strcmpopt_8.c (working copy) @@ -0,0 +1,177 @@ +/* PR tree-optimization/92683 - strncmp incorrect result with equal substrings + and nonconst bound + { dg-do compile } + { dg-options "-O1 -Wall -fdump-tree-forwprop1" } */ + +#define SIZE_MAX __SIZE_MAX__ + +#define S123 "123" +#define S1234 "1234" + +typedef __SIZE_TYPE__ size_t; + +#ifndef ident +# define ident(n) n +#endif + +extern void failure_on_line (int); + +/* Verify that the test in 'if (EQL strncmp (S, T, N))' is folded. */ +#define T(eql, s, t, n) do { \ + max = ident (n); \ + if (!(eql __builtin_strncmp (s, t, max))) \ + failure_on_line (__LINE__); \ + } while (0) + +void test_literal (void) +{ + size_t max; + + T (0 ==, S123, S1234, 0); + T (0 ==, S123, S1234, 1); + T (0 ==, S123, S1234, 2); + T (0 ==, S123, S1234, 3); + T (0 >, S123, S1234, 4); + T (0 >, S123, S1234, 5); + T (0 >, S123, S1234, SIZE_MAX - 2); + T (0 >, S123, S1234, SIZE_MAX - 1); + T (0 >, S123, S1234, SIZE_MAX); + + T (0 ==, S123 + 1, S1234, 0); + T (0 <, S123 + 1, S1234, 1); + T (0 <, S123 + 1, S1234, 2); + T (0 <, S123 + 1, S1234, 3); + T (0 <, S123 + 1, S1234, 4); + T (0 <, S123 + 1, S1234, SIZE_MAX - 2); + T (0 <, S123 + 1, S1234, SIZE_MAX - 1); + T (0 <, S123 + 1, S1234, SIZE_MAX); + + T (0 ==, S123 + 1, S1234 + 1, 0); + T (0 ==, S123 + 1, S1234 + 1, 1); + T (0 ==, S123 + 1, S1234 + 1, 2); + T (0 >, S123 + 1, S1234 + 1, 3); + T (0 >, S123 + 1, S1234 + 1, SIZE_MAX - 1); + T (0 >, S123 + 1, S1234 + 1, SIZE_MAX); + + T (0 ==, S123 + 3, S1234 + 1, 0); + T (0 >, S123 + 3, S1234 + 1, 1); + T (0 >, S123 + 3, S1234 + 1, 2); + T (0 >, S123 + 3, S1234 + 1, 3); + T (0 >, S123 + 3, S1234 + 1, SIZE_MAX - 1); + T (0 >, S123 + 3, S1234 + 1, SIZE_MAX); + + int zero = 0; + + T (zero ==, S123, S1234, 0); + T (zero ==, S123, S1234, 1); + T (zero ==, S123, S1234, 2); + T (zero ==, S123, S1234, 3); + T (zero >, S123, S1234, 4); + T (zero >, S123, S1234, 5); + T (zero >, S123, S1234, SIZE_MAX - 2); + T (zero >, S123, S1234, SIZE_MAX - 1); + T (zero >, S123, S1234, SIZE_MAX); + + T (zero ==, S123 + 1, S1234, 0); + T (zero <, S123 + 1, S1234, 1); + T (zero <, S123 + 1, S1234, 2); + T (zero <, S123 + 1, S1234, 3); + T (zero <, S123 + 1, S1234, 4); + T (zero <, S123 + 1, S1234, SIZE_MAX - 2); + T (zero <, S123 + 1, S1234, SIZE_MAX - 1); + T (zero <, S123 + 1, S1234, SIZE_MAX); + + T (zero ==, S123 + 1, S1234 + 1, 0); + T (zero ==, S123 + 1, S1234 + 1, 1); + T (zero ==, S123 + 1, S1234 + 1, 2); + T (zero >, S123 + 1, S1234 + 1, 3); + T (zero >, S123 + 1, S1234 + 1, SIZE_MAX - 1); + T (zero >, S123 + 1, S1234 + 1, SIZE_MAX); + + T (zero ==, S123 + 3, S1234 + 1, 0); + T (zero >, S123 + 3, S1234 + 1, 1); + T (zero >, S123 + 3, S1234 + 1, 2); + T (zero >, S123 + 3, S1234 + 1, 3); + T (zero >, S123 + 3, S1234 + 1, SIZE_MAX - 1); + T (zero >, S123 + 3, S1234 + 1, SIZE_MAX); +} + +const char s123[] = S123; +const char s1234[] = S1234; + +void test_cst_array (void) +{ + size_t max; + + T (0 ==, s123, s1234, 0); + T (0 ==, s123, s1234, 1); + T (0 ==, s123, s1234, 2); + T (0 ==, s123, s1234, 3); + T (0 >, s123, s1234, 4); + T (0 >, s123, s1234, 5); + T (0 >, s123, s1234, SIZE_MAX - 2); + T (0 >, s123, s1234, SIZE_MAX - 1); + T (0 >, s123, s1234, SIZE_MAX); + + T (0 ==, s123 + 1, s1234, 0); + T (0 <, s123 + 1, s1234, 1); + T (0 <, s123 + 1, s1234, 2); + T (0 <, s123 + 1, s1234, 3); + T (0 <, s123 + 1, s1234, 4); + T (0 <, s123 + 1, s1234, SIZE_MAX - 2); + T (0 <, s123 + 1, s1234, SIZE_MAX - 1); + T (0 <, s123 + 1, s1234, SIZE_MAX); + + T (0 ==, s123 + 1, s1234 + 1, 0); + T (0 ==, s123 + 1, s1234 + 1, 1); + T (0 ==, s123 + 1, s1234 + 1, 2); + T (0 >, s123 + 1, s1234 + 1, 3); + T (0 >, s123 + 1, s1234 + 1, SIZE_MAX - 1); + T (0 >, s123 + 1, s1234 + 1, SIZE_MAX); + + T (0 ==, s123 + 3, s1234 + 1, 0); + T (0 >, s123 + 3, s1234 + 1, 1); + T (0 >, s123 + 3, s1234 + 1, 2); + T (0 >, s123 + 3, s1234 + 1, 3); + T (0 >, s123 + 3, s1234 + 1, SIZE_MAX - 1); + T (0 >, s123 + 3, s1234 + 1, SIZE_MAX); + + int zero = 0; + + T (zero ==, s123, s1234, 0); + T (zero ==, s123, s1234, 1); + T (zero ==, s123, s1234, 2); + T (zero ==, s123, s1234, 3); + T (zero >, s123, s1234, 4); + T (zero >, s123, s1234, 5); + T (zero >, s123, s1234, SIZE_MAX - 2); + T (zero >, s123, s1234, SIZE_MAX - 1); + T (zero >, s123, s1234, SIZE_MAX); + + T (zero ==, s123 + 1, s1234, 0); + T (zero <, s123 + 1, s1234, 1); + T (zero <, s123 + 1, s1234, 2); + T (zero <, s123 + 1, s1234, 3); + T (zero <, s123 + 1, s1234, 4); + T (zero <, s123 + 1, s1234, SIZE_MAX - 2); + T (zero <, s123 + 1, s1234, SIZE_MAX - 1); + T (zero <, s123 + 1, s1234, SIZE_MAX); + + T (zero ==, s123 + 1, s1234 + 1, 0); + T (zero ==, s123 + 1, s1234 + 1, 1); + T (zero ==, s123 + 1, s1234 + 1, 2); + T (zero >, s123 + 1, s1234 + 1, 3); + T (zero >, s123 + 1, s1234 + 1, SIZE_MAX - 1); + T (zero >, s123 + 1, s1234 + 1, SIZE_MAX); + + T (zero ==, s123 + 3, s1234 + 1, 0); + T (zero >, s123 + 3, s1234 + 1, 1); + T (zero >, s123 + 3, s1234 + 1, 2); + T (zero >, s123 + 3, s1234 + 1, 3); + T (zero >, s123 + 3, s1234 + 1, SIZE_MAX - 1); + T (zero >, s123 + 3, s1234 + 1, SIZE_MAX); +} + +/* { dg-final { scan-tree-dump-not "strcmp" "forwprop1" } } + { dg-final { scan-tree-dump-not "strncmp" "forwprop1" } } + { dg-final { scan-tree-dump-not "failure_on_line_" "forwprop1" } } */ Index: gcc/testsuite/gcc.dg/strcmpopt_9.c =================================================================== --- gcc/testsuite/gcc.dg/strcmpopt_9.c (nonexistent) +++ gcc/testsuite/gcc.dg/strcmpopt_9.c (working copy) @@ -0,0 +1,34 @@ +/* PR tree-optimization/92683 - strncmp incorrect result with equal substrings + and nonconst bound + { dg-do run } + { dg-options "-O2 -Wall" } */ + +#include "strlenopt.h" + +#define ident(n) ident (n) + +__attribute__ ((noclone, noinline, noipa)) size_t +ident (size_t x) +{ + return x; +} + +int nfails; + +__attribute__ ((noclone, noinline, noipa)) void +failure_on_line (int line) +{ + __builtin_printf ("failure on line %i\n", line); + ++nfails; +} + +#include "strcmpopt_8.c" + +int main (void) +{ + test_literal (); + test_cst_array (); + + if (nfails) + __builtin_abort (); +}