Hi, The attached patch tries to fix PR82665 by adding value-range for 'n' to [0, PTRDIFF_MAX - 1] in the following case: def = memchr(arg, 0, sz); n = def - arg
where def and arg are char *. I suppose it's safe to assume that if arg is char *, then memchr(arg, 0, sz) would return a non NULL pointer ? The patch could also be extended to handle more functions like memrchr, but I was wondering if it is in right direction ? Bootstrapped+tested on x86_64-unknown-linux-gnu and cross-tested on arm*-*-*, aarch64*-*-*. Thanks, Prathamesh
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr82665.c b/gcc/testsuite/gcc.dg/tree-ssa/pr82665.c new file mode 100644 index 00000000000..17be6ec4e4b --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr82665.c @@ -0,0 +1,22 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +void f1 (char *p, __SIZE_TYPE__ sz) +{ + char *q = __builtin_memchr (p, 0, sz); + long n = q - p; + + if (n >= __PTRDIFF_MAX__) + __builtin_abort (); +} + +void f2 (unsigned char *p, __SIZE_TYPE__ sz) +{ + unsigned char *q = __builtin_memchr (p, 0, sz); + long n = q - p; + + if (n >= __PTRDIFF_MAX__) + __builtin_abort (); +} + +/* { dg-final { scan-tree-dump-times "memchr" 1 "optimized" } } */ diff --git a/gcc/vr-values.c b/gcc/vr-values.c index 3e760a378fc..ca9dca84ebc 100644 --- a/gcc/vr-values.c +++ b/gcc/vr-values.c @@ -773,6 +773,54 @@ vr_values::extract_range_from_binary_expr (value_range *vr, extract_range_from_binary_expr_1 (vr, code, expr_type, &vr0, &vr1); + /* Set value_range for n in following sequence: + def = __builtin_memchr (arg, 0, sz) + op0 = convert_expr def + op1 = convert_expr arg + n = op0 - op1 + Here the range for n can be set to [0, PTRDIFF_MAX - 1]. */ + + if (vr->type == VR_VARYING + && (code == MINUS_EXPR) + && (TREE_CODE (op0) == SSA_NAME) + && (TREE_CODE (op1) == SSA_NAME) + && INTEGRAL_TYPE_P (TREE_TYPE (op0)) + && INTEGRAL_TYPE_P (TREE_TYPE (op1))) + { + tree def = NULL_TREE; + tree arg = NULL_TREE; + + gassign *s = dyn_cast<gassign *> (SSA_NAME_DEF_STMT (op0)); + if (s && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (s))) + def = gimple_assign_rhs1 (s); + + s = dyn_cast<gassign *> (SSA_NAME_DEF_STMT (op1)); + if (s && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (s))) + arg = gimple_assign_rhs1 (s); + + gcall *call_stmt = NULL; + if (def && arg + && (TREE_CODE (def) == SSA_NAME) + && ((TREE_CODE (TREE_TYPE (def)) == POINTER_TYPE) + && (TREE_TYPE (TREE_TYPE (def)) == char_type_node)) + && (TREE_CODE (arg) == SSA_NAME) + && ((TREE_CODE (TREE_TYPE (arg)) == POINTER_TYPE) + && (TREE_TYPE (TREE_TYPE (arg)) == char_type_node)) + && (call_stmt = dyn_cast<gcall *>(SSA_NAME_DEF_STMT (def))) + && (gimple_call_combined_fn (call_stmt) == CFN_BUILT_IN_MEMCHR) + && operand_equal_p (def, gimple_call_lhs (call_stmt), 0) + && operand_equal_p (arg, gimple_call_arg (call_stmt, 0), 0) + && integer_zerop (gimple_call_arg (call_stmt, 1))) + { + tree max = vrp_val_max (ptrdiff_type_node); + wide_int wmax = wi::to_wide (max, TYPE_PRECISION (TREE_TYPE (max))); + tree range_min = build_zero_cst (expr_type); + tree range_max = wide_int_to_tree (expr_type, wmax - 1); + set_value_range (vr, VR_RANGE, range_min, range_max, NULL); + return; + } + } + /* Try harder for PLUS and MINUS if the range of one operand is symbolic and based on the other operand, for example if it was deduced from a symbolic comparison. When a bound of the range of the first operand