== Administrivia ==
This is my first patch. I have emailed in the signed copyright transfer
documents already.
== Description ==
This patch is a fix for Bug 53001
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 both -Wconversion (since it is a
subset) and -Wextra (as suggested on the Bug 53001 discussion)
Because this changes -Wextra, when compiling with -Werror and -Wextra,
some code will not compile now. The code in gcc that this occurred in
was changed to use explicit casts. The patch would be shorter if
-Wextra did not enable -Wfloat-conversion, and if that is desired I can
change the patch.
Because this patch enables it for -Wextra, gcc/c-family/c-cppbuiltin.c,
gcc/mcf.c, gcc/predict.c, gcc/real.c and libcpp/symtab.c need to be
changed, otherwise they would be unmodified.
I am not certain that c.opt was modified correctly.
== Testcases ==
This patch has passes the existing -Wconversion testcases.
gcc/testsuite/c-c++-common/Wconversion-real.c and other testcases
possibly could be modified.
== Changelog ==
2013-10-08 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-cppbuiltin.c Making explicit casts
* gcc/c-family/c.opt Adding new warning float-conversion and
enabling it with -Wextra and -Wconversion
* gcc/doc/invoke.texi Adding documentation about
-Wfloat-conversion
* gcc/mcf.c Making explicit casts
* gcc/predict.c Making explicit casts
* gcc/real.c Making explicit casts
* libcpp/symtab.c Avoiding float to int conversion
== Bootstrapping and testing ==
Tested bootstrap on x86_64-unknown-linux-gnu for
--enable-languages=c,c++,fortran,java,lto,objc with trunk on r203051 and
r203112
Thank you for consideration of this patch.
Joshua Cogliati
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-cppbuiltin.c
===================================================================
--- gcc/c-family/c-cppbuiltin.c (revision 203112)
+++ gcc/c-family/c-cppbuiltin.c (working copy)
@@ -157,7 +157,7 @@ builtin_define_float_constants (const ch
p log10 b if b is a power of 10
floor((p - 1) log10 b) otherwise
*/
- dig = (fmt->p - 1) * log10_b;
+ dig = (int)((fmt->p - 1) * log10_b);
sprintf (name, "__%s_DIG__", name_prefix);
builtin_define_with_int_value (name, dig);
@@ -173,7 +173,7 @@ builtin_define_float_constants (const ch
Recall that emin is negative, so the integer truncation calculates
the ceiling, not the floor, in this case. */
- min_10_exp = (fmt->emin - 1) * log10_b;
+ min_10_exp = (int)((fmt->emin - 1) * log10_b);
sprintf (name, "__%s_MIN_10_EXP__", name_prefix);
sprintf (buf, "(%d)", min_10_exp);
builtin_define_with_value (name, buf, 0);
@@ -208,7 +208,7 @@ builtin_define_float_constants (const ch
Hand-waving aside, crunching all of the sets of constants above by hand
does not yield a case for which the first term is significant, which
in the end is all that matters. */
- max_10_exp = fmt->emax * log10_b;
+ max_10_exp = (int)(fmt->emax * log10_b);
sprintf (name, "__%s_MAX_10_EXP__", name_prefix);
builtin_define_with_int_value (name, max_10_exp);
@@ -224,14 +224,14 @@ builtin_define_float_constants (const ch
{
double d_decimal_dig
= 1 + (fmt->p < ldfmt->p ? ldfmt->p : fmt->p) * log10_b;
- decimal_dig = d_decimal_dig;
+ decimal_dig = (int)d_decimal_dig;
if (decimal_dig < d_decimal_dig)
decimal_dig++;
}
/* Similar, for this type rather than long double. */
{
double type_d_decimal_dig = 1 + fmt->p * log10_b;
- type_decimal_dig = type_d_decimal_dig;
+ type_decimal_dig = (int)type_d_decimal_dig;
if (type_decimal_dig < type_d_decimal_dig)
type_decimal_dig++;
}
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) EnabledBy(Wextra)
+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
@@ -3351,6 +3352,7 @@ name is still supported, but the newer n
-Wuninitialized @gol
-Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
-Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
+-Wfloat-conversion @gol
}
The option @option{-Wextra} also prints warning messages for the
@@ -4570,6 +4572,14 @@ 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} or @option{-Wextra}.
+
@item -Wsizeof-pointer-memaccess
@opindex Wsizeof-pointer-memaccess
@opindex Wno-sizeof-pointer-memaccess
Index: gcc/mcf.c
===================================================================
--- gcc/mcf.c (revision 203112)
+++ gcc/mcf.c (working copy)
@@ -348,8 +348,8 @@ mcf_sqrt (double x)
gcc_assert (x >= 0);
- convertor.floatPart = x;
- convertor2.floatPart = x;
+ convertor.floatPart = (float)x;
+ convertor2.floatPart = (float)x;
convertor.intPart = MAGIC_CONST1 + (convertor.intPart >> 1);
convertor2.intPart = MAGIC_CONST2 - (convertor2.intPart >> 1);
Index: gcc/predict.c
===================================================================
--- gcc/predict.c (revision 203112)
+++ gcc/predict.c (working copy)
@@ -792,7 +792,7 @@ combine_predictions_for_insn (rtx insn,
/* If one probability is 0% and one 100%, avoid division by zero. */
combined_probability = REG_BR_PROB_BASE / 2;
else
- combined_probability = (((double) combined_probability) * probability
+ combined_probability = (int)(((double) combined_probability) * probability
* REG_BR_PROB_BASE / d + 0.5);
}
@@ -957,7 +957,7 @@ combine_predictions_for_bb (basic_block
/* If one probability is 0% and one 100%, avoid division by zero. */
combined_probability = REG_BR_PROB_BASE / 2;
else
- combined_probability = (((double) combined_probability)
+ combined_probability = (int)(((double) combined_probability)
* probability
* REG_BR_PROB_BASE / d + 0.5);
}
Index: gcc/real.c
===================================================================
--- gcc/real.c (revision 203112)
+++ gcc/real.c (working copy)
@@ -1550,14 +1550,14 @@ real_to_decimal_for_mode (char *str, con
}
/* Bound the number of digits printed by the size of the representation. */
- max_digits = SIGNIFICAND_BITS * M_LOG10_2;
+ max_digits = (int)(SIGNIFICAND_BITS * M_LOG10_2);
if (digits == 0 || digits > max_digits)
digits = max_digits;
/* Estimate the decimal exponent, and compute the length of the string it
will print as. Be conservative and add one to account for possible
overflow or rounding error. */
- dec_exp = REAL_EXP (&r) * M_LOG10_2;
+ dec_exp = (int)(REAL_EXP (&r) * M_LOG10_2);
for (max_digits = 1; dec_exp ; max_digits++)
dec_exp /= 10;
@@ -2215,7 +2215,7 @@ decimal_integer_string (char *str, const
sign = r.sign;
r.sign = 0;
- dec_exp = REAL_EXP (&r) * M_LOG10_2;
+ dec_exp = (int)(REAL_EXP (&r) * M_LOG10_2);
digits = dec_exp + 1;
gcc_assert ((digits + 2) < (int)buf_size);
@@ -2818,7 +2818,7 @@ significand_size (enum machine_mode mode
than the number of bits required to hold the largest coefficient
of this mode. */
double log2_10 = 3.3219281;
- return fmt->p * log2_10;
+ return (int)(fmt->p * log2_10);
}
return fmt->p;
}
Index: libcpp/symtab.c
===================================================================
--- libcpp/symtab.c (revision 203112)
+++ libcpp/symtab.c (working copy)
@@ -287,7 +287,8 @@ ht_dump_statistics (cpp_hash_table *tabl
: (x) / (1024*1024))))
#define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
- total_bytes = longest = sum_of_squares = nids = 0;
+ total_bytes = longest = nids = 0;
+ sum_of_squares = 0.0;
p = table->entries;
limit = p + table->nslots;
do
