Changes compared to previous version of patch:
This patch only includes -Wfloat-conversion in -Wconversion, it does not
include it in -Wextra
It also changes several testcases to use -Wfloat-conversion instead of
-Wconversion
A split out patch to make the floating conversions explicit is attached
at the PR 53001 page, but is not included in this patch.
On 10/09/2013 02:38 PM, Joseph S. Myers wrote:
> Also note that this patch needs to add testcases to the testsuite
> (gcc/testsuite/c-c++-common/, probably) testing what cases generate
> warnings with the new option and what cases don't.
>
=== Description ===
As required by the C and C++ standards, gcc automatically converts
floating point numbers to lower precision or integer values. Silently
converting these values is a problem for numerical programs. GCC
already has a flag -Wconversion which does warn about these conversions,
but -Wconversion also warns about integer conversion which means for
many programs the number of warnings will be large.
This patch adds a -Wfloat-conversion that only warns on float
conversions. Here are three examples that are warned by this new flag:
int main(int argc, char ** argv) {
int i = 3.14;
return i;
}
int foo(double x)
{
return x;
}
float foo2(double x) {
return x;
}
The -Wfloat-conversion is enabled by -Wconversion (since it is a
subset)
It was suggested on the discussion for bug 53001 that this be enabled by
-Wextra, but this version of the patch does not.
I am not certain that c.opt was modified correctly.
== Testcases ==
This patch has passes the existing -Wconversion testcases. It modifies
Wconversion-real.c, Wconversion-real-integer.c and pr35635.c to be more
specific
== Changelog ==
2013-10-13 Joshua Cogliati <jrinc...@yahoo.com>
Splitting out a -Wfloat-conversion from -Wconversion for
conversions that lower floating point number precision
or conversion from floating point numbers to integers
* gcc/c-family/c-common.c Switching unsafe_conversion_p to
return an enumeration with more detail, and conversion_warning
to use this information.
* gcc/c-family/c-common.h Adding conversion_safety enumeration
and switching return type of unsafe_conversion_p
* gcc/c-family/c.opt Adding new warning float-conversion and
enabling it -Wconversion
* gcc/doc/invoke.texi Adding documentation about
-Wfloat-conversion
* gcc/testsuite/c-c++-common/Wconversion-real.c Switching tests
to use float-conversion
* gcc/testsuite/gcc.dg/Wconversion-real-integer.c Switching
tests to use float-conversion
* gcc/testsuite/gcc.dg/pr35635.c Switching tests to use
float-conversion
== Bootstrapping and testing ==
Tested bootstrap on x86_64-unknown-linux-gnu for
--enable-languages=c,c++,fortran,java,lto,objc with trunk on r203112
Thank you for consideration of this patch.
Index: gcc/c-family/c-common.c
===================================================================
--- gcc/c-family/c-common.c (revision 203112)
+++ gcc/c-family/c-common.c (working copy)
@@ -2517,10 +2517,10 @@ shorten_binary_op (tree result_type, tre
Function allows conversions between types of different signedness and
does not return true in that case. Function can produce signedness
warnings if PRODUCE_WARNS is true. */
-bool
+enum conversion_safety
unsafe_conversion_p (tree type, tree expr, bool produce_warns)
{
- bool give_warning = false;
+ enum conversion_safety give_warning = SAFE_CONVERSION; /* is 0 or false */
tree expr_type = TREE_TYPE (expr);
location_t loc = EXPR_LOC_OR_HERE (expr);
@@ -2532,7 +2532,7 @@ unsafe_conversion_p (tree type, tree exp
&& TREE_CODE (type) == INTEGER_TYPE)
{
if (!real_isinteger (TREE_REAL_CST_PTR (expr), TYPE_MODE (expr_type)))
- give_warning = true;
+ give_warning = UNSAFE_REAL;
}
/* Warn for an integer constant that does not fit into integer type. */
else if (TREE_CODE (expr_type) == INTEGER_TYPE
@@ -2553,7 +2553,7 @@ unsafe_conversion_p (tree type, tree exp
" constant value to negative integer");
}
else
- give_warning = true;
+ give_warning = UNSAFE_OTHER;
}
else if (TREE_CODE (type) == REAL_TYPE)
{
@@ -2562,7 +2562,7 @@ unsafe_conversion_p (tree type, tree exp
{
REAL_VALUE_TYPE a = real_value_from_int_cst (0, expr);
if (!exact_real_truncate (TYPE_MODE (type), &a))
- give_warning = true;
+ give_warning = UNSAFE_REAL;
}
/* Warn for a real constant that does not fit into a smaller
real type. */
@@ -2571,7 +2571,7 @@ unsafe_conversion_p (tree type, tree exp
{
REAL_VALUE_TYPE a = TREE_REAL_CST (expr);
if (!exact_real_truncate (TYPE_MODE (type), &a))
- give_warning = true;
+ give_warning = UNSAFE_REAL;
}
}
}
@@ -2580,7 +2580,7 @@ unsafe_conversion_p (tree type, tree exp
/* Warn for real types converted to integer types. */
if (TREE_CODE (expr_type) == REAL_TYPE
&& TREE_CODE (type) == INTEGER_TYPE)
- give_warning = true;
+ give_warning = UNSAFE_REAL;
else if (TREE_CODE (expr_type) == INTEGER_TYPE
&& TREE_CODE (type) == INTEGER_TYPE)
@@ -2618,7 +2618,7 @@ unsafe_conversion_p (tree type, tree exp
&& int_fits_type_p (op1, c_common_signed_type (type))
&& int_fits_type_p (op1,
c_common_unsigned_type (type))))
- return false;
+ return SAFE_CONVERSION;
/* If constant is unsigned and fits in the target
type, then the result will also fit. */
else if ((TREE_CODE (op0) == INTEGER_CST
@@ -2627,12 +2627,12 @@ unsafe_conversion_p (tree type, tree exp
|| (TREE_CODE (op1) == INTEGER_CST
&& unsigned1
&& int_fits_type_p (op1, type)))
- return false;
+ return SAFE_CONVERSION;
}
}
/* Warn for integer types converted to smaller integer types. */
if (TYPE_PRECISION (type) < TYPE_PRECISION (expr_type))
- give_warning = true;
+ give_warning = UNSAFE_OTHER;
/* When they are the same width but different signedness,
then the value may change. */
@@ -2668,14 +2668,14 @@ unsafe_conversion_p (tree type, tree exp
if (!exact_real_truncate (TYPE_MODE (type), &real_low_bound)
|| !exact_real_truncate (TYPE_MODE (type), &real_high_bound))
- give_warning = true;
+ give_warning = UNSAFE_OTHER;
}
/* Warn for real types converted to smaller real types. */
else if (TREE_CODE (expr_type) == REAL_TYPE
&& TREE_CODE (type) == REAL_TYPE
&& TYPE_PRECISION (type) < TYPE_PRECISION (expr_type))
- give_warning = true;
+ give_warning = UNSAFE_REAL;
}
return give_warning;
@@ -2689,8 +2689,9 @@ conversion_warning (tree type, tree expr
{
tree expr_type = TREE_TYPE (expr);
location_t loc = EXPR_LOC_OR_HERE (expr);
+ enum conversion_safety conversion_kind;
- if (!warn_conversion && !warn_sign_conversion)
+ if (!warn_conversion && !warn_sign_conversion && !warn_float_conversion)
return;
switch (TREE_CODE (expr))
@@ -2717,10 +2718,19 @@ conversion_warning (tree type, tree expr
case REAL_CST:
case INTEGER_CST:
- if (unsafe_conversion_p (type, expr, true))
- warning_at (loc, OPT_Wconversion,
- "conversion to %qT alters %qT constant value",
- type, expr_type);
+ conversion_kind = unsafe_conversion_p (type, expr, true);
+ if(conversion_kind == UNSAFE_REAL)
+ {
+ warning_at (loc, OPT_Wfloat_conversion,
+ "conversion to %qT alters %qT constant value",
+ type, expr_type);
+ }
+ else if(conversion_kind)
+ {
+ warning_at (loc, OPT_Wconversion,
+ "conversion to %qT alters %qT constant value",
+ type, expr_type);
+ }
return;
case COND_EXPR:
@@ -2736,10 +2746,19 @@ conversion_warning (tree type, tree expr
}
default: /* 'expr' is not a constant. */
- if (unsafe_conversion_p (type, expr, true))
- warning_at (loc, OPT_Wconversion,
- "conversion to %qT from %qT may alter its value",
- type, expr_type);
+ conversion_kind = unsafe_conversion_p (type, expr, true);
+ if(conversion_kind == UNSAFE_REAL)
+ {
+ warning_at (loc, OPT_Wfloat_conversion,
+ "conversion to %qT from %qT may alter its value",
+ type, expr_type);
+ }
+ else if(conversion_kind)
+ {
+ warning_at (loc, OPT_Wconversion,
+ "conversion to %qT from %qT may alter its value",
+ type, expr_type);
+ }
}
}
Index: gcc/c-family/c-common.h
===================================================================
--- gcc/c-family/c-common.h (revision 203112)
+++ gcc/c-family/c-common.h (working copy)
@@ -685,6 +685,16 @@ struct visibility_flags
unsigned inlines_hidden : 1; /* True when -finlineshidden in effect. */
};
+/* These variables are possible types of unsafe conversions.
+ SAFE_CONVERSION The conversion is safe
+ UNSAFE_OTHER Another type of conversion with problems
+ UNSAFE_SIGN Conversion between signed and unsigned integers
+ which are all warned about immediately, so this is unused
+ UNSAFE_REAL Conversions that reduce the precision of reals
+ including conversions from reals to integers
+ */
+enum conversion_safety { SAFE_CONVERSION = 0, UNSAFE_OTHER, UNSAFE_SIGN, UNSAFE_REAL };
+
/* Global visibility options. */
extern struct visibility_flags visibility_options;
@@ -738,7 +748,7 @@ extern tree c_common_signed_type (tree);
extern tree c_common_signed_or_unsigned_type (int, tree);
extern void c_common_init_ts (void);
extern tree c_build_bitfield_integer_type (unsigned HOST_WIDE_INT, int);
-extern bool unsafe_conversion_p (tree, tree, bool);
+extern enum conversion_safety unsafe_conversion_p (tree, tree, bool);
extern bool decl_with_nonnull_addr_p (const_tree);
extern tree c_fully_fold (tree, bool, bool *);
extern tree decl_constant_value_for_optimization (tree);
Index: gcc/c-family/c.opt
===================================================================
--- gcc/c-family/c.opt (revision 203112)
+++ gcc/c-family/c.opt (working copy)
@@ -387,6 +387,10 @@ Werror-implicit-function-declaration
C ObjC RejectNegative Warning Alias(Werror=, implicit-function-declaration)
This switch is deprecated; use -Werror=implicit-function-declaration instead
+Wfloat-conversion
+C ObjC C++ ObjC++ Var(warn_float_conversion) LangEnabledBy(C ObjC C++ ObjC++,Wconversion)
+Warn for implicit type conversions that cause loss of floating point precision
+
Wfloat-equal
C ObjC C++ ObjC++ Var(warn_float_equal) Warning
Warn if testing floating point numbers for equality
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi (revision 203112)
+++ gcc/doc/invoke.texi (working copy)
@@ -263,7 +263,8 @@ Objective-C and Objective-C++ Dialects}.
-Wpointer-arith -Wno-pointer-to-int-cast @gol
-Wredundant-decls -Wno-return-local-addr @gol
-Wreturn-type -Wsequence-point -Wshadow @gol
--Wsign-compare -Wsign-conversion -Wsizeof-pointer-memaccess @gol
+-Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
+-Wsizeof-pointer-memaccess @gol
-Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
-Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
@@ -4570,6 +4571,14 @@ value, like assigning a signed integer e
integer variable. An explicit cast silences the warning. In C, this
option is enabled also by @option{-Wconversion}.
+@item -Wfloat-conversion
+@opindex Wfloat-conversion
+@opindex Wno-float-conversion
+Warn for implicit conversions that reduce the precision of a real value.
+This includes conversions from real to integer, and from higher precision
+real to lower precision real values. This option is also enabled by
+@option{-Wconversion}.
+
@item -Wsizeof-pointer-memaccess
@opindex Wsizeof-pointer-memaccess
@opindex Wno-sizeof-pointer-memaccess
Index: gcc/testsuite/c-c++-common/Wconversion-real.c
===================================================================
--- gcc/testsuite/c-c++-common/Wconversion-real.c (revision 203112)
+++ gcc/testsuite/c-c++-common/Wconversion-real.c (working copy)
@@ -2,8 +2,8 @@
/* { dg-do compile } */
/* { dg-skip-if "doubles are floats" { "avr-*-*" } { "*" } { "" } } */
-/* { dg-options "-std=c99 -Wconversion" { target c } } */
-/* { dg-options "-Wconversion" { target c++ } } */
+/* { dg-options "-std=c99 -Wfloat-conversion" { target c } } */
+/* { dg-options "-Wfloat-conversion" { target c++ } } */
/* { dg-require-effective-target large_double } */
float vfloat;
@@ -20,18 +20,18 @@ void h (void)
double d = 0;
long double ld = 0;
- ffloat (3.1); /* { dg-warning "conversion" } */
- vfloat = 3.1; /* { dg-warning "conversion" } */
- ffloat (3.1L); /* { dg-warning "conversion" } */
- vfloat = 3.1L; /* { dg-warning "conversion" } */
- fdouble (3.1L); /* { dg-warning "conversion" "" { target large_long_double } } */
- vdouble = 3.1L; /* { dg-warning "conversion" "" { target large_long_double } } */
- ffloat (vdouble); /* { dg-warning "conversion" } */
- vfloat = vdouble; /* { dg-warning "conversion" } */
- ffloat (vlongdouble); /* { dg-warning "conversion" } */
- vfloat = vlongdouble; /* { dg-warning "conversion" } */
- fdouble (vlongdouble); /* { dg-warning "conversion" "" { target large_long_double } } */
- vdouble = vlongdouble; /* { dg-warning "conversion" "" { target large_long_double } } */
+ ffloat (3.1); /* { dg-warning "float-conversion" } */
+ vfloat = 3.1; /* { dg-warning "float-conversion" } */
+ ffloat (3.1L); /* { dg-warning "float-conversion" } */
+ vfloat = 3.1L; /* { dg-warning "float-conversion" } */
+ fdouble (3.1L); /* { dg-warning "float-conversion" "" { target large_long_double } } */
+ vdouble = 3.1L; /* { dg-warning "float-conversion" "" { target large_long_double } } */
+ ffloat (vdouble); /* { dg-warning "float-conversion" } */
+ vfloat = vdouble; /* { dg-warning "float-conversion" } */
+ ffloat (vlongdouble); /* { dg-warning "float-conversion" } */
+ vfloat = vlongdouble; /* { dg-warning "float-conversion" } */
+ fdouble (vlongdouble); /* { dg-warning "float-conversion" "" { target large_long_double } } */
+ vdouble = vlongdouble; /* { dg-warning "float-conversion" "" { target large_long_double } } */
ffloat ((float) 3.1);
Index: gcc/testsuite/gcc.dg/Wconversion-real-integer.c
===================================================================
--- gcc/testsuite/gcc.dg/Wconversion-real-integer.c (revision 203112)
+++ gcc/testsuite/gcc.dg/Wconversion-real-integer.c (working copy)
@@ -25,18 +25,18 @@ void h (void)
float f = 3;
double d = 3;
- fsi (3.1f); /* { dg-warning "conversion" } */
- si = 3.1f; /* { dg-warning "conversion" } */
- fsi (3.1); /* { dg-warning "conversion" } */
- si = 3.1; /* { dg-warning "conversion" } */
- fsi (d); /* { dg-warning "conversion" } */
- si = d; /* { dg-warning "conversion" } */
+ fsi (3.1f); /* { dg-warning "float-conversion" } */
+ si = 3.1f; /* { dg-warning "float-conversion" } */
+ fsi (3.1); /* { dg-warning "float-conversion" } */
+ si = 3.1; /* { dg-warning "float-conversion" } */
+ fsi (d); /* { dg-warning "float-conversion" } */
+ si = d; /* { dg-warning "float-conversion" } */
fui (-1.0); /* { dg-warning "overflow" } */
ui = -1.0; /* { dg-warning "overflow" } */
- ffloat (INT_MAX); /* { dg-warning "conversion" } */
- vfloat = INT_MAX; /* { dg-warning "conversion" } */
- ffloat (16777217); /* { dg-warning "conversion" } */
- vfloat = 16777217; /* { dg-warning "conversion" } */
+ ffloat (INT_MAX); /* { dg-warning "float-conversion" } */
+ vfloat = INT_MAX; /* { dg-warning "float-conversion" } */
+ ffloat (16777217); /* { dg-warning "float-conversion" } */
+ vfloat = 16777217; /* { dg-warning "float-conversion" } */
ffloat (si); /* { dg-warning "conversion" } */
vfloat = si; /* { dg-warning "conversion" } */
ffloat (ui); /* { dg-warning "conversion" } */
Index: gcc/testsuite/gcc.dg/pr35635.c
===================================================================
--- gcc/testsuite/gcc.dg/pr35635.c (revision 203112)
+++ gcc/testsuite/gcc.dg/pr35635.c (working copy)
@@ -45,7 +45,7 @@ void func2()
/* At least one branch of ? does not fit in the destination, thus
warn. */
- schar_x = bar != 0 ? 2.1 : 10; /* { dg-warning "conversion" } */
+ schar_x = bar != 0 ? 2.1 : 10; /* { dg-warning "float-conversion" } */
schar_x = bar != 0 ? (signed char) 1024: -1024; /* { dg-warning "conversion" } */
}
@@ -61,7 +61,7 @@ void func3()
/* At least one branch of ? does not fit in the destination, thus
warn. */
- uchar_x = bar != 0 ? 2.1 : 10; /* { dg-warning "conversion" } */
+ uchar_x = bar != 0 ? 2.1 : 10; /* { dg-warning "float-conversion" } */
uchar_x = bar != 0
? (unsigned char) 1024
: -1; /* { dg-warning "negative integer implicitly converted to unsigned type" } */
