@@ -789,6 +789,18 @@ c_common_post_options (const char **pfilename)
&& flag_unsafe_math_optimizations == 0)
flag_fp_contract_mode = FP_CONTRACT_OFF;
+ /* If we are compiling C, and we are outside of a standards mode,
+ we can permit the new values from ISO/IEC TS 18661-3 for
+ FLT_EVAL_METHOD. Otherwise, we must restrict the possible values to
+ the set specified in ISO C99/C11. */
+ if (!flag_iso
+ && !c_dialect_cxx ()
+ && (global_options_set.x_flag_permitted_flt_eval_methods
+ == PERMITTED_FLT_EVAL_METHODS_DEFAULT))
+ flag_permitted_flt_eval_methods = PERMITTED_FLT_EVAL_METHODS_TS_18661;
+ else
+ flag_permitted_flt_eval_methods = PERMITTED_FLT_EVAL_METHODS_C11;
+
/* By default we use C99 inline semantics in GNU99 or C99 mode. C99
inline semantics are not supported in GNU89 or C89 mode. */
if (flag_gnu89_inline == -1)
@@ -1305,6 +1305,21 @@ Enum(excess_precision) String(fast) Value(EXCESS_PRECISION_FAST)
EnumValue
Enum(excess_precision) String(standard) Value(EXCESS_PRECISION_STANDARD)
+; Whether we permit the extended set of values for FLT_EVAL_METHOD
+; introduced in ISO/IEC TS 18661-3, or limit ourselves to those in C99/C11.
+fpermitted-flt-eval-methods=
+Common Joined RejectNegative Enum(permitted_flt_eval_methods) Var(flag_permitted_flt_eval_methods) Init(PERMITTED_FLT_EVAL_METHODS_DEFAULT)
+-fpermitted-flt-eval-methods=[c11|ts-18661] Specify which values of FLT_EVAL_METHOD are permitted.
+
+Enum
+Name(permitted_flt_eval_methods) Type(enum permitted_flt_eval_methods) UnknownError(unknown specification for the set of FLT_EVAL_METHOD values to permit %qs)
+
+EnumValue
+Enum(permitted_flt_eval_methods) String(c11) Value(PERMITTED_FLT_EVAL_METHODS_C11)
+
+EnumValue
+Enum(permitted_flt_eval_methods) String(ts-18661-3) Value(PERMITTED_FLT_EVAL_METHODS_TS_18661)
+
ffast-math
Common Optimization
@@ -375,7 +375,8 @@ Objective-C and Objective-C++ Dialects}.
-flto-partition=@var{alg} -fmerge-all-constants @gol
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
-fmove-loop-invariants -fno-branch-count-reg @gol
--fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol
+-fno-defer-pop -fno-fp-int-builtin-inexact @gol
+-fpermitted-flt-eval-methods=@var{standard} -fno-function-cse @gol
-fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol
-fno-peephole2 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
@@ -8917,6 +8918,30 @@ Even if @option{-fno-fp-int-builtin-inexact} is used, if the functions
generate a call to a library function then the ``inexact'' exception
may be raised if the library implementation does not follow TS 18661.
+@item -fpermitted-flt-eval-methods=@var{style}
+@opindex fpermitted-flt-eval-methods
+@opindex fpermitted-flt-eval-methods=c11
+@opindex fpermitted-flt-eval-methods=ts-18661-3
+ISO/IEC TS 18661-3 defines new permissible values for
+@code{FLT_EVAL_METHOD} that indicate that operations and constants with
+a semantic type that is an interchange or extended format should be
+evaluated to the precision and range of that type. These new values are
+a superset of those permitted under C99/C11, which does not specify the
+meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code
+conforming to C11 may not have been written expecting the possibility of
+the new values.
+
+@option{-fpermitted-flt-eval-methods} specifies whether the compiler
+should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11,
+or the extended set of values specified in ISO/IEC TS 18661-3.
+
+@var{style} is either @code{c11} or @code{ts-18661-3} as appropriate.
+
+The default when in a standards compliant mode (@option{-std=c11} or similar)
+is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU
+dialect (@option{-std=gnu11} or similar) is
+@option{-fpermitted-flt-eval-methods=ts-18661-3}.
+
@item -fsingle-precision-constant
@opindex fsingle-precision-constant
Treat floating-point constants as single precision instead of
@@ -158,6 +158,14 @@ enum excess_precision
EXCESS_PRECISION_STANDARD
};
+/* The options for which values of FLT_EVAL_METHOD are permissible. */
+enum permitted_flt_eval_methods
+{
+ PERMITTED_FLT_EVAL_METHODS_DEFAULT,
+ PERMITTED_FLT_EVAL_METHODS_TS_18661,
+ PERMITTED_FLT_EVAL_METHODS_C11
+};
+
/* Type of stack check. */
enum stack_check_type
{
new file mode 100644
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-options "-std=c11" } */
+
+/* Test that we only see the C99/C11 values for __FLT_EVAL_METHOD__ if
+ we are compiling with -std=c11. */
+
+int main (int argc, char** argv)
+{
+ switch (__FLT_EVAL_METHOD__)
+ {
+ case 0:
+ case 1:
+ case 2:
+ case -1:
+ return 0;
+ default:
+ return 1;
+ }
+}
new file mode 100644
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-options "-fpermitted-flt-eval-methods=c11" } */
+
+/* Test that we only see the C99/C11 values for __FLT_EVAL_METHOD__ if
+ we are compiling with -fpermitted-flt-eval-methods=c11. */
+
+int main (int argc, char** argv)
+{
+ switch (__FLT_EVAL_METHOD__)
+ {
+ case 0:
+ case 1:
+ case 2:
+ case -1:
+ return 0;
+ default:
+ return 1;
+ }
+}
Hi, This option is added to control which values of FLT_EVAL_METHOD the compiler is allowed to set. ISO/IEC TS 18661-3 defines new permissible values for FLT_EVAL_METHOD that indicate that operations and constants with a semantic type that is an interchange or extended format should be evaluated to the precision and range of that type. These new values are a superset of those permitted under C99/C11, which does not specify the meaning of other positive values of FLT_EVAL_METHOD. As such, code conforming to C11 may not have been written expecting the possibility of the new values. -fpermitted-flt-eval-methods specifies whether the compiler should allow only the values of FLT_EVAL_METHOD specified in C99/C11, or the extended set of values specified in ISO/IEC TS 18661-3. The two possible values this option can take are "c11" or "ts-18661-3". The default when in a standards compliant mode (-std=c11 or similar) is -fpermitted-flt-eval-methods=c11. The default when in a GNU dialect (-std=gnu11 or similar) is -fpermitted-flt-eval-methods=ts-18661-3. I've added two testcases which test that when this option, or a C standards dialect, would restrict the range of values to {-1, 0, 1, 2}, those are the only values we see. At this stage in the patch series this trivially holds for all targets. Bootstrapped on x86_64 with no issues and tested in series on AArch64. OK? Thanks, James --- gcc/c-family/ 2016-09-30 James Greenhalgh <james.greenhalgh@arm.com> * c-opts.c (c_common_post_options): Add logic to handle the default case for -fpermitted-flt-eval-methods. gcc/ 2016-09-30 James Greenhalgh <james.greenhalgh@arm.com> * common.opt (fpermitted-flt-eval-methods): New. * doc/invoke.texi (-fpermitted-flt-eval-methods): Document it. * flag_types.h (permitted_flt_eval_methods): New. gcc/testsuite/ 2016-09-30 James Greenhalgh <james.greenhalgh@arm.com> * gcc.dg/fpermitted-flt-eval-methods_1.c: New. * gcc.dg/fpermitted-flt-eval-methods_2.c: New.