---
This patch has already been approved:
https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01554.html
---
This patch ports the logic from s390's TARGET_FLT_EVAL_METHOD to the new
target hook TARGET_C_EXCESS_PRECISION, following the guidance in this thread
https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01172.html
In this patch we handle EXCESS_PRECISION_TYPE_IMPLICIT like
EXCESS_PRECISION_TYPE_FAST. This has the consequence of meaning float_t in
glibc is calculated in a different precision (double) to that indicated by
FLT_EVAL_METHOD.
---
gcc/
2016-11-09 James Greenhalgh <james.greenha...@arm.com>
* config/s390/s390.c (s390_excess_precision): New.
(TARGET_C_EXCESS_PRECISION): Define.
diff --git a/gcc/config/s390/s390.c b/gcc/config/s390/s390.c
index 3f98cd8..311a7f2 100644
--- a/gcc/config/s390/s390.c
+++ b/gcc/config/s390/s390.c
@@ -15260,6 +15260,43 @@ s390_invalid_binary_op (int op ATTRIBUTE_UNUSED, const_tree type1, const_tree ty
return NULL;
}
+/* Implement TARGET_C_EXCESS_PRECISION.
+
+ FIXME: For historical reasons, float_t and double_t are typedef'ed to
+ double on s390, causing operations on float_t to operate in a higher
+ precision than is necessary. However, it is not the case that SFmode
+ operations have implicit excess precision, and we generate more optimal
+ code if we let the compiler know no implicit extra precision is added.
+
+ That means when we are compiling with -fexcess-precision=fast, the value
+ we set for FLT_EVAL_METHOD will be out of line with the actual precision of
+ float_t (though they would be correct for -fexcess-precision=standard).
+
+ A complete fix would modify glibc to remove the unnecessary typedef
+ of float_t to double. */
+
+static enum flt_eval_method
+s390_excess_precision (enum excess_precision_type type)
+{
+ switch (type)
+ {
+ case EXCESS_PRECISION_TYPE_IMPLICIT:
+ case EXCESS_PRECISION_TYPE_FAST:
+ /* The fastest type to promote to will always be the native type,
+ whether that occurs with implicit excess precision or
+ otherwise. */
+ return FLT_EVAL_METHOD_PROMOTE_TO_FLOAT;
+ case EXCESS_PRECISION_TYPE_STANDARD:
+ /* Otherwise, when we are in a standards compliant mode, to
+ ensure consistency with the implementation in glibc, report that
+ float is evaluated to the range and precision of double. */
+ return FLT_EVAL_METHOD_PROMOTE_TO_DOUBLE;
+ default:
+ gcc_unreachable ();
+ }
+ return FLT_EVAL_METHOD_UNPREDICTABLE;
+}
+
/* Initialize GCC target structure. */
#undef TARGET_ASM_ALIGNED_HI_OP
@@ -15320,6 +15357,9 @@ s390_invalid_binary_op (int op ATTRIBUTE_UNUSED, const_tree type1, const_tree ty
#undef TARGET_ASM_CAN_OUTPUT_MI_THUNK
#define TARGET_ASM_CAN_OUTPUT_MI_THUNK hook_bool_const_tree_hwi_hwi_const_tree_true
+#undef TARGET_C_EXCESS_PRECISION
+#define TARGET_C_EXCESS_PRECISION s390_excess_precision
+
#undef TARGET_SCHED_ADJUST_PRIORITY
#define TARGET_SCHED_ADJUST_PRIORITY s390_adjust_priority
#undef TARGET_SCHED_ISSUE_RATE
