Hi,
as you know we have a -Wcast-align warning which works only for
STRICT_ALIGNMENT targets. But occasionally it would be nice to be
able to switch this warning on even for other targets.
Therefore I would like to add a strict version of this option
which can be invoked with -Wcast-align=strict. With the only
difference that it does not depend on STRICT_ALIGNMENT.
I used the code from check_effective_target_non_strict_align
in target-supports.exp for the first version of the test case,
where we have this:
return [check_no_compiler_messages non_strict_align assembly {
char *y;
typedef char __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__))) c;
c *z;
void foo(void) { z = (c *) y; }
} "-Wcast-align"]
... and to my big surprise it did _not_ work for C++ as-is,
because same_type_p considers differently aligned types identical,
and therefore cp_build_c_cast tries the conversion first via a
const_cast which succeeds, but did not emit the cast-align warning
in this case.
As a work-around I had to check the alignment in build_const_cast_1
as well.
Bootstrapped and reg-tested on x86_64-pc-linux-gnu.
Is it OK for trunk?
Thanks
Bernd.
gcc:
2017-09-03 Bernd Edlinger <[email protected]>
* common.opt (Wcast-align=strict): New warning option.
* doc/invoke.texi: Document -Wcast-align=strict.
c:
2017-09-03 Bernd Edlinger <[email protected]>
* c-typeck.c (build_c_cast): Implement -Wcast-align=strict.
cp:
2017-09-03 Bernd Edlinger <[email protected]>
* typeck.c (build_reinterpret_cast_1,
build_const_cast_1): Implement -Wcast-align=strict.
testsuite:
2017-09-03 Bernd Edlinger <[email protected]>
* c-c++-common/Wcast-align.c: New test.
Index: gcc/c/c-typeck.c
===================================================================
--- gcc/c/c-typeck.c (revision 251617)
+++ gcc/c/c-typeck.c (working copy)
@@ -5578,7 +5578,7 @@ build_c_cast (location_t loc, tree type, tree expr
}
/* Warn about possible alignment problems. */
- if (STRICT_ALIGNMENT
+ if ((STRICT_ALIGNMENT || warn_cast_align == 2)
&& TREE_CODE (type) == POINTER_TYPE
&& TREE_CODE (otype) == POINTER_TYPE
&& TREE_CODE (TREE_TYPE (otype)) != VOID_TYPE
Index: gcc/common.opt
===================================================================
--- gcc/common.opt (revision 251617)
+++ gcc/common.opt (working copy)
@@ -564,6 +564,10 @@ Wcast-align
Common Var(warn_cast_align) Warning
Warn about pointer casts which increase alignment.
+Wcast-align=strict
+Common Var(warn_cast_align,2) Warning
+Warn about pointer casts which increase alignment.
+
Wcpp
Common Var(warn_cpp) Init(1) Warning
Warn when a #warning directive is encountered.
Index: gcc/cp/typeck.c
===================================================================
--- gcc/cp/typeck.c (revision 251617)
+++ gcc/cp/typeck.c (working copy)
@@ -7265,8 +7265,8 @@ build_reinterpret_cast_1 (tree type, tree expr, bo
complain))
return error_mark_node;
/* Warn about possible alignment problems. */
- if (STRICT_ALIGNMENT && warn_cast_align
- && (complain & tf_warning)
+ if ((STRICT_ALIGNMENT || warn_cast_align == 2)
+ && (complain & tf_warning)
&& !VOID_TYPE_P (type)
&& TREE_CODE (TREE_TYPE (intype)) != FUNCTION_TYPE
&& COMPLETE_TYPE_P (TREE_TYPE (type))
@@ -7273,7 +7273,7 @@ build_reinterpret_cast_1 (tree type, tree expr, bo
&& COMPLETE_TYPE_P (TREE_TYPE (intype))
&& TYPE_ALIGN (TREE_TYPE (type)) > TYPE_ALIGN (TREE_TYPE (intype)))
warning (OPT_Wcast_align, "cast from %qH to %qI "
- "increases required alignment of target type", intype, type);
+ "increases required alignment of target type", intype, type);
/* We need to strip nops here, because the front end likes to
create (int *)&a for array-to-pointer decay, instead of &a[0]. */
@@ -7447,6 +7447,14 @@ build_const_cast_1 (tree dst_type, tree expr, tsub
the user is making a potentially unsafe cast. */
check_for_casting_away_constness (src_type, dst_type,
CAST_EXPR, complain);
+ /* ??? comp_ptr_ttypes_const ignores TYPE_ALIGN. */
+ if ((STRICT_ALIGNMENT || warn_cast_align == 2)
+ && (complain & tf_warning)
+ && TYPE_ALIGN (TREE_TYPE (dst_type))
+ > TYPE_ALIGN (TREE_TYPE (src_type)))
+ warning (OPT_Wcast_align, "cast from %qH to %qI "
+ "increases required alignment of target type",
+ src_type, dst_type);
}
if (reference_type)
{
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi (revision 251617)
+++ gcc/doc/invoke.texi (working copy)
@@ -266,7 +266,8 @@ Objective-C and Objective-C++ Dialects}.
-Wno-attributes -Wbool-compare -Wbool-operation @gol
-Wno-builtin-declaration-mismatch @gol
-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol
--Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual @gol
+-Wc++-compat -Wc++11-compat -Wc++14-compat @gol
+-Wcast-align -Wcast-align=strict -Wcast-qual @gol
-Wchar-subscripts -Wchkp -Wcatch-value -Wcatch-value=@var{n} @gol
-Wclobbered -Wcomment -Wconditionally-supported @gol
-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdangling-else -Wdate-time @gol
@@ -5923,6 +5924,12 @@ target is increased. For example, warn if a @code
an @code{int *} on machines where integers can only be accessed at
two- or four-byte boundaries.
+@item -Wcast-align=strict
+@opindex Wcast-align=strict
+Warn whenever a pointer is cast such that the required alignment of the
+target is increased. For example, warn if a @code{char *} is cast to
+an @code{int *} regardless of the target machine.
+
@item -Wwrite-strings
@opindex Wwrite-strings
@opindex Wno-write-strings
Index: gcc/testsuite/c-c++-common/Wcast-align.c
===================================================================
--- gcc/testsuite/c-c++-common/Wcast-align.c (revision 0)
+++ gcc/testsuite/c-c++-common/Wcast-align.c (working copy)
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-Wcast-align=strict" } */
+
+typedef char __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__))) c;
+typedef struct __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__)))
+{
+ char x;
+} d;
+
+char *x;
+c *y;
+d *z;
+
+void
+foo (void)
+{
+ y = (c *) x; /* { dg-warning "alignment" } */
+ z = (d *) x; /* { dg-warning "alignment" } */
+}
