From 0a0b3574de3a5965eebb920d3da48771710ef94b Mon Sep 17 00:00:00 2001 From: Mark Mitchell Date: Sun, 5 Sep 2010 21:50:46 +0000 Subject: [PATCH] c.opt (Wdouble-promotion): New. * c.opt (Wdouble-promotion): New. * doc/invoke.texi: Document -Wdouble-promotion. * c-typeck.c (convert_arguments): Check for implicit conversions from float to double. (do_warn_double_promotion): New function. (build_conditional_expr): Use it. (build_binary_op): Likewise. * gcc.dg/Wdouble-promotion.c: New. From-SVN: r163884 --- gcc/ChangeLog | 9 ++ gcc/c-family/ChangeLog | 4 + gcc/c-family/c.opt | 4 + gcc/c-typeck.c | 54 +++++++++++- gcc/doc/invoke.texi | 28 +++++- gcc/testsuite/ChangeLog | 4 + gcc/testsuite/gcc.dg/Wdouble-promotion.c | 104 +++++++++++++++++++++++ 7 files changed, 203 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/Wdouble-promotion.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index daef269e1dc6..1edae2f11077 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,12 @@ +2010-09-05 Mark Mitchell + + * doc/invoke.texi: Document -Wdouble-promotion. + * c-typeck.c (convert_arguments): Check for implicit conversions + from float to double. + (do_warn_double_promotion): New function. + (build_conditional_expr): Use it. + (build_binary_op): Likewise. + 2010-09-05 Richard Guenther PR tree-optimization/45535 diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog index 84abcd1d9151..0a6aaa5d5954 100644 --- a/gcc/c-family/ChangeLog +++ b/gcc/c-family/ChangeLog @@ -1,3 +1,7 @@ +2010-09-05 Mark Mitchell + + * c.opt (Wdouble-promotion): New. + 2010-09-02 Joseph Myers * c.opt (falt-external-templates, fhuge-objects, fvtable-gc, diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt index 68d59296e43b..a997f79cf8c5 100644 --- a/gcc/c-family/c.opt +++ b/gcc/c-family/c.opt @@ -266,6 +266,10 @@ Wimplicit C ObjC Var(warn_implicit) Init(-1) Warning Warn about implicit declarations +Wdouble-promotion +C ObjC C++ ObjC++ Var(warn_double_promotion) Warning +Warn about implicit conversions from \"float\" to \"double\" + Wimplicit-function-declaration C ObjC Var(warn_implicit_function_declaration) Init(-1) Warning Warn about implicit function declarations diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c index 164cda8d54ec..87c51104038e 100644 --- a/gcc/c-typeck.c +++ b/gcc/c-typeck.c @@ -3106,8 +3106,15 @@ convert_arguments (tree typelist, VEC(tree,gc) *values, if (type_generic) parmval = val; else - /* Convert `float' to `double'. */ - parmval = convert (double_type_node, val); + { + /* Convert `float' to `double'. */ + if (warn_double_promotion && !c_inhibit_evaluation_warnings) + warning (OPT_Wdouble_promotion, + "implicit conversion from %qT to %qT when passing " + "argument to function", + valtype, double_type_node); + parmval = convert (double_type_node, val); + } } else if (excess_precision && !type_generic) /* A "double" argument with excess precision being passed @@ -4029,6 +4036,40 @@ ep_convert_and_check (tree type, tree expr, tree semantic_type) return convert (type, expr); } +/* RESULT_TYPE is the result of converting TYPE1 and TYPE2 to a common + type via c_common_type. If -Wdouble-promotion is in use, and the + conditions for warning have been met, issue a warning. GMSGID is + the warning message. It must have two %T specifiers for the type + that was converted (generally "float") and the type to which it was + converted (generally "double), respectively. LOC is the location + to which the awrning should refer. */ + +static void +do_warn_double_promotion (tree result_type, tree type1, tree type2, + const char *gmsgid, location_t loc) +{ + tree source_type; + + if (!warn_double_promotion) + return; + /* If the conversion will not occur at run-time, there is no need to + warn about it. */ + if (c_inhibit_evaluation_warnings) + return; + if (TYPE_MAIN_VARIANT (result_type) != double_type_node + && TYPE_MAIN_VARIANT (result_type) != complex_double_type_node) + return; + if (TYPE_MAIN_VARIANT (type1) == float_type_node + || TYPE_MAIN_VARIANT (type1) == complex_float_type_node) + source_type = type1; + else if (TYPE_MAIN_VARIANT (type2) == float_type_node + || TYPE_MAIN_VARIANT (type2) == complex_float_type_node) + source_type = type2; + else + return; + warning_at (loc, OPT_Wdouble_promotion, gmsgid, source_type, result_type); +} + /* Build and return a conditional expression IFEXP ? OP1 : OP2. If IFEXP_BCP then the condition is a call to __builtin_constant_p, and if folded to an integer constant then the unselected half may @@ -4140,6 +4181,10 @@ build_conditional_expr (location_t colon_loc, tree ifexp, bool ifexp_bcp, || code2 == COMPLEX_TYPE)) { result_type = c_common_type (type1, type2); + do_warn_double_promotion (result_type, type1, type2, + "implicit conversion from %qT to %qT to " + "match other result of conditional", + colon_loc); /* If -Wsign-compare, warn here if type1 and type2 have different signedness. We'll promote the signed to unsigned @@ -9822,6 +9867,11 @@ build_binary_op (location_t location, enum tree_code code, if (shorten || common || short_compare) { result_type = c_common_type (type0, type1); + do_warn_double_promotion (result_type, type0, type1, + "implicit conversion from %qT to %qT " + "to match other operand of binary " + "expression", + location); if (result_type == error_mark_node) return error_mark_node; } diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 797a66024333..95bfe6c9ba2a 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -235,8 +235,8 @@ Objective-C and Objective-C++ Dialects}. -Wchar-subscripts -Wclobbered -Wcomment @gol -Wconversion -Wcoverage-mismatch -Wcpp -Wno-deprecated @gol -Wno-deprecated-declarations -Wdisabled-optimization @gol --Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol --Werror -Werror=* @gol +-Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol +-Wno-endif-labels -Werror -Werror=* @gol -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol -Wformat-security -Wformat-y2k @gol @@ -3053,6 +3053,30 @@ This warning is enabled by @option{-Wall}. Suppress warning messages emitted by @code{#warning} directives. +@item -Wdouble-promotion @r{(C and Objective-C only)} +@opindex Wdouble-promotion +@opindex Wno-double-promotion +Give a warning when a value of type @code{float} is implicitly +promoted to @code{double}. CPUs with a 32-bit ``single-precision'' +floating-point unit implement @code{float} in hardware, but emulate +@code{double} in software. On such a machine, doing computations +using @code{double} values is much more expensive because of the +overhead required for software emulation. + +It is easy to accidentally do computations with @code{double} because +floating-point literals are implicitly of type @code{double}. For +example, in: +@smallexample +@group +float area(float radius) +@{ + return 3.14159 * radius * radius; +@} +@end group +@end smallexample +the compiler will perform the entire computation with @code{double} +because the floating-point literal is a @code{double}. + @item -Wformat @opindex Wformat @opindex Wno-format diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 4aefdc1dc88d..316811e0f216 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2010-09-05 Mark Mitchell + + * gcc.dg/Wdouble-promotion.c: New. + 2010-09-05 Tobias Burnus * gfortran.dg/float128_1.f90: Remove test case as diff --git a/gcc/testsuite/gcc.dg/Wdouble-promotion.c b/gcc/testsuite/gcc.dg/Wdouble-promotion.c new file mode 100644 index 000000000000..d7a61899f7fb --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wdouble-promotion.c @@ -0,0 +1,104 @@ +/* { dg-do compile } */ +/* { dg-options "-Wdouble-promotion" } */ + +#include + +/* Some targets do not provide so we define I ourselves. */ +#define I 1.0iF +#define ID ((_Complex double)I) + +float f; +double d; +int i; +long double ld; +_Complex float cf; +_Complex double cd; +_Complex long double cld; +size_t s; + +extern void unprototyped_fn (); +extern void varargs_fn (int, ...); +extern void double_fn (double); +extern float float_fn (void); + +void +usual_arithmetic_conversions(void) +{ + float local_f; + _Complex float local_cf; + + /* Values of type "float" are implicitly converted to "double" or + "long double" due to use in arithmetic with "double" or "long + double" operands. */ + local_f = f + 1.0; /* { dg-warning "implicit" } */ + local_f = f - d; /* { dg-warning "implicit" } */ + local_f = 1.0f * 1.0; /* { dg-warning "implicit" } */ + local_f = 1.0f / d; /* { dg-warning "implicit" } */ + + local_cf = cf + 1.0; /* { dg-warning "implicit" } */ + local_cf = cf - d; /* { dg-warning "implicit" } */ + local_cf = cf + 1.0 * ID; /* { dg-warning "implicit" } */ + local_cf = cf - cd; /* { dg-warning "implicit" } */ + + local_f = i ? f : d; /* { dg-warning "implicit" } */ + i = f == d; /* { dg-warning "implicit" } */ + i = d != f; /* { dg-warning "implicit" } */ +} + +void +default_argument_promotion (void) +{ + /* Because there is no prototype, "f" is promoted to "double". */ + unprototyped_fn (f); /* { dg-warning "implicit" } */ + undeclared_fn (f); /* { dg-warning "implicit" } */ + /* Because "f" is part of the variable argument list, it is promoted + to "double". */ + varargs_fn (1, f); /* { dg-warning "implicit" } */ +} + +/* There is no warning when an explicit cast is used to perform the + conversion. */ + +void +casts (void) +{ + float local_f; + _Complex float local_cf; + + local_f = (double)f + 1.0; /* { dg-bogus "implicit" } */ + local_f = (double)f - d; /* { dg-bogus "implicit" } */ + local_f = (double)1.0f + 1.0; /* { dg-bogus "implicit" } */ + local_f = (double)1.0f - d; /* { dg-bogus "implicit" } */ + + local_cf = (_Complex double)cf + 1.0; /* { dg-bogus "implicit" } */ + local_cf = (_Complex double)cf - d; /* { dg-bogus "implicit" } */ + local_cf = (_Complex double)cf + 1.0 * ID; /* { dg-bogus "implicit" } */ + local_cf = (_Complex double)cf - cd; /* { dg-bogus "implicit" } */ + + local_f = i ? (double)f : d; /* { dg-bogus "implicit" } */ + i = (double)f == d; /* { dg-bogus "implicit" } */ + i = d != (double)f; /* { dg-bogus "implicit" } */ +} + +/* There is no warning on conversions that occur in assignment (and + assignment-like) contexts. */ + +void +assignments (void) +{ + d = f; /* { dg-bogus "implicit" } */ + double_fn (f); /* { dg-bogus "implicit" } */ + d = float_fn (); /* { dg-bogus "implicit" } */ +} + +/* There is no warning in non-evaluated contexts. */ + +void +non_evaluated (void) +{ + s = sizeof (f + 1.0); /* { dg-bogus "implicit" } */ + s = __alignof__ (f + 1.0); /* { dg-bogus "implicit" } */ + d = (__typeof__(f + 1.0))f; /* { dg-bogus "implicit" } */ + s = sizeof (i ? f : d); /* { dg-bogus "implicit" } */ + s = sizeof (unprototyped_fn (f)); /* { dg-bogus "implicit" } */ +} -- 2.43.5