Sadly, dstbase is the PARM_DECL for d. That's where things are going
"wrong". Not sure why you're getting the PARM_DECL in that case. I'd
debug get_addr_base_and_unit_offset to understand what's going on.
Essentially you're getting different results of
get_addr_base_and_unit_offset in a case where they arguably should be
the same.
Probably get_attr_nonstring_decl has the same "mistake" and returns
the PARM_DECL instead of the SSA name pointer. So we're comparing
apples and oranges here.
Returning the SSA_NAME_VAR from get_attr_nonstring_decl() is
intentional but the function need not (perhaps should not)
also set *REF to it.
Yeah:
/* If EXPR refers to a character array or pointer declared attribute
nonstring return a decl for that array or pointer and set *REF to
the referenced enclosing object or pointer. Otherwise returns
null. */
tree
get_attr_nonstring_decl (tree expr, tree *ref)
{
tree decl = expr;
if (TREE_CODE (decl) == SSA_NAME)
{
gimple *def = SSA_NAME_DEF_STMT (decl);
if (is_gimple_assign (def))
{
tree_code code = gimple_assign_rhs_code (def);
if (code == ADDR_EXPR
|| code == COMPONENT_REF
|| code == VAR_DECL)
decl = gimple_assign_rhs1 (def);
}
else if (tree var = SSA_NAME_VAR (decl))
decl = var;
}
if (TREE_CODE (decl) == ADDR_EXPR)
decl = TREE_OPERAND (decl, 0);
if (ref)
*ref = decl;
I see a lot of "magic" here again in the attempt to "propagate"
a nonstring attribute.
That's the function's purpose: to look for the attribute. Is
there a better way to do this?
Note
foo (char *p __attribute__(("nonstring")))
{
p = "bar";
strlen (p); // or whatever is necessary to call get_attr_nonstring_decl
}
is perfectly valid and p as passed to strlen is _not_ nonstring(?).
I don't know if you're saying that it should get a warning or
shouldn't. Right now it doesn't because the strlen() call is
folded before we check for nonstring.
I could see an argument for diagnosing it but I suspect you
wouldn't like it because it would mean more warning from
the folder. I could also see an argument against it because,
as you said, it's safe.
If you take the assignment to p away then a warning is issued,
and that's because p is declared with attribute nonstring.
That's also why get_attr_nonstring_decl looks at SSA_NAME_VAR.
I think in your code comparing bases you want to look at the _original_
argument to the string function rather than what get_attr_nonstring_decl
returned as ref.
I've adjusted get_attr_nonstring_decl() to avoid setting *REF
to SSA_NAME_VAR. That let me remove the GIMPLE_NOP code from
the patch. I've also updated the comment above SSA_NAME_VAR
to clarify its purpose per Jeff's comments.
Attached is an updated revision with these changes.
Martin
PR tree-optimization/87028 - false positive -Wstringop-truncation strncpy with global variable source string
gcc/ChangeLog:
PR tree-optimization/87028
* calls.c (get_attr_nonstring_decl): Avoid setting *REF to
SSA_NAME_VAR.
* gimple-fold.c (gimple_fold_builtin_strncpy): Avoid folding
when statement doesn't belong to a basic block.
* tree.h (SSA_NAME_VAR): Update comment.
* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Simplify.
gcc/testsuite/ChangeLog:
PR tree-optimization/87028
* c-c++-common/Wstringop-truncation.c: Remove xfails.
* gcc.dg/Wstringop-truncation-5.c: New test.
Index: gcc/tree.h
===================================================================
--- gcc/tree.h (revision 263925)
+++ gcc/tree.h (working copy)
@@ -1697,7 +1697,10 @@ extern tree maybe_wrap_with_location (tree, locati
: NULL_TREE)
/* Returns the variable being referenced. This can be NULL_TREE for
- temporaries not associated with any user variable.
+ temporaries not associated with any user variable. The result
+ is mainly useful for debugging, diagnostics, or as the target
+ declaration referenced by an SSA_NAME. Otherwise, because
+ it has no dataflow information, it should not be used.
Once released, this is the only field that can be relied upon. */
#define SSA_NAME_VAR(NODE) \
(SSA_NAME_CHECK (NODE)->ssa_name.var == NULL_TREE \
Index: gcc/calls.c
===================================================================
--- gcc/calls.c (revision 263928)
+++ gcc/calls.c (working copy)
@@ -1503,6 +1503,7 @@ tree
get_attr_nonstring_decl (tree expr, tree *ref)
{
tree decl = expr;
+ tree var = NULL_TREE;
if (TREE_CODE (decl) == SSA_NAME)
{
gimple *def = SSA_NAME_DEF_STMT (decl);
@@ -1515,17 +1516,25 @@ get_attr_nonstring_decl (tree expr, tree *ref)
|| code == VAR_DECL)
decl = gimple_assign_rhs1 (def);
}
- else if (tree var = SSA_NAME_VAR (decl))
- decl = var;
+ else
+ var = SSA_NAME_VAR (decl);
}
if (TREE_CODE (decl) == ADDR_EXPR)
decl = TREE_OPERAND (decl, 0);
+ /* To simplify calling code, store the referenced DECL regardless of
+ the attribute determined below, but avoid storing the SSA_NAME_VAR
+ obtained above (it's not useful for dataflow purposes). */
if (ref)
*ref = decl;
- if (TREE_CODE (decl) == ARRAY_REF)
+ /* Use the SSA_NAME_VAR that was determined above to see if it's
+ declared nonstring. Otherwise drill down into the referenced
+ DECL. */
+ if (var)
+ decl = var;
+ else if (TREE_CODE (decl) == ARRAY_REF)
decl = TREE_OPERAND (decl, 0);
else if (TREE_CODE (decl) == COMPONENT_REF)
decl = TREE_OPERAND (decl, 1);
Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c (revision 263925)
+++ gcc/gimple-fold.c (working copy)
@@ -1702,6 +1702,11 @@ gimple_fold_builtin_strncpy (gimple_stmt_iterator
if (tree_int_cst_lt (ssize, len))
return false;
+ /* Defer warning (and folding) until the next statement in the basic
+ block is reachable. */
+ if (!gimple_bb (stmt))
+ return false;
+
/* Diagnose truncation that leaves the copy unterminated. */
maybe_diag_stxncpy_trunc (*gsi, src, len);
Index: gcc/tree-ssa-strlen.c
===================================================================
--- gcc/tree-ssa-strlen.c (revision 263925)
+++ gcc/tree-ssa-strlen.c (working copy)
@@ -1904,8 +1904,6 @@ maybe_diag_stxncpy_trunc (gimple_stmt_iterator gsi
if (TREE_CODE (dstdecl) == ADDR_EXPR)
dstdecl = TREE_OPERAND (dstdecl, 0);
- tree ref = NULL_TREE;
-
if (!sidx)
{
/* If the source is a non-string return early to avoid warning
@@ -1914,12 +1912,14 @@ maybe_diag_stxncpy_trunc (gimple_stmt_iterator gsi
tree srcdecl = gimple_call_arg (stmt, 1);
if (TREE_CODE (srcdecl) == ADDR_EXPR)
srcdecl = TREE_OPERAND (srcdecl, 0);
- if (get_attr_nonstring_decl (srcdecl, &ref))
+ if (get_attr_nonstring_decl (srcdecl, NULL))
return false;
}
- /* Likewise, if the destination refers to a an array/pointer declared
- nonstring return early. */
+ /* Likewise, if the destination refers to an array/pointer declared
+ nonstring return early. REF will be set to the referenced enclosing
+ object or pointer either way. */
+ tree ref;
if (get_attr_nonstring_decl (dstdecl, &ref))
return false;
Index: gcc/testsuite/c-c++-common/Wstringop-truncation.c
===================================================================
--- gcc/testsuite/c-c++-common/Wstringop-truncation.c (revision 263925)
+++ gcc/testsuite/c-c++-common/Wstringop-truncation.c (working copy)
@@ -329,9 +329,8 @@ void test_strncpy_array (Dest *pd, int i, const ch
of the array to NUL is not diagnosed. */
{
/* This might be better written using memcpy() but it's safe so
- it probably shouldn't be diagnosed. It currently triggers
- a warning because of bug 81704. */
- strncpy (dst7, "0123456", sizeof dst7); /* { dg-bogus "\\\[-Wstringop-truncation]" "bug 81704" { xfail *-*-* } } */
+ it isn't diagnosed. See pr81704 and pr87028. */
+ strncpy (dst7, "0123456", sizeof dst7); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
dst7[sizeof dst7 - 1] = '\0';
sink (dst7);
}
@@ -350,7 +349,7 @@ void test_strncpy_array (Dest *pd, int i, const ch
}
{
- strncpy (pd->a5, "01234", sizeof pd->a5); /* { dg-bogus "\\\[-Wstringop-truncation]" "bug 81704" { xfail *-*-* } } */
+ strncpy (pd->a5, "01234", sizeof pd->a5); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
pd->a5[sizeof pd->a5 - 1] = '\0';
sink (pd);
}
Index: gcc/testsuite/gcc.dg/Wstringop-truncation-5.c
===================================================================
--- gcc/testsuite/gcc.dg/Wstringop-truncation-5.c (nonexistent)
+++ gcc/testsuite/gcc.dg/Wstringop-truncation-5.c (working copy)
@@ -0,0 +1,64 @@
+/* PR tree-optimization/87028 - false positive -Wstringop-truncation
+ strncpy with global variable source string
+ { dg-do compile }
+ { dg-options "-O2 -Wstringop-truncation" } */
+
+char *strncpy (char *, const char *, __SIZE_TYPE__);
+
+#define STR "1234567890"
+
+struct S
+{
+ char a[5], b[5];
+};
+
+const char arr[] = STR;
+const char* const ptr = STR;
+
+const char arr2[][10] = { "123", STR };
+
+void test_literal (struct S *s)
+{
+ strncpy (s->a, STR, sizeof s->a - 1); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+ s->a[sizeof s->a - 1] = '\0';
+}
+
+void test_global_arr (struct S *s)
+{
+ strncpy (s->a, arr, sizeof s->a - 1); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+ s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_global_arr2 (struct S *s)
+{
+ strncpy (s->a, arr2[1], sizeof s->a - 1); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+ s->a [sizeof s->a - 1] = '\0';
+
+ strncpy (s->b, arr2[0], sizeof s->a - 1);
+}
+
+void test_global_ptr (struct S *s)
+{
+ strncpy (s->a, ptr, sizeof s->a - 1); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+ s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_local_arr (struct S *s)
+{
+ const char arr[] = STR;
+ strncpy (s->a, arr, sizeof s->a - 1);
+ s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_local_ptr (struct S *s)
+{
+ const char* const ptr = STR;
+ strncpy (s->a, ptr, sizeof s->a - 1); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+ s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_compound_literal (struct S *s)
+{
+ strncpy (s->a, (char[]){ STR }, sizeof s->a - 1);
+ s->a [sizeof s->a - 1] = '\0';
+}
