[Patch i386] PR78509 - TARGET_C_EXCESS_PRECISION should not return

 "unpredictable" for EXCESS_PRECISION_TYPE_STANDARD

gcc/

	PR target/78509
	* config/i386/i386.c (i386_excess_precision): Do not return
	FLT_EVAL_METHOD_UNPREDICTABLE when "type" is
	EXCESS_PRECISION_TYPE_STANDARD.
	* target.def (excess_precision): Document that targets should
	not return FLT_EVAL_METHOD_UNPREDICTABLE when "type" is
	EXCESS_PRECISION_TYPE_STANDARD or EXCESS_PRECISION_TYPE_FAST.
	Fix typo in first sentence.
	* doc/tm.texi: Regenerate.

From-SVN: r242866

4 files changed, 39 insertions, 14 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a0db22e..0878c30 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,15 @@
+2016-11-24  James Greenahlgh  <james.greenhalgh@arm.com>
+
+	PR target/78509
+	* config/i386/i386.c (i386_excess_precision): Do not return
+	FLT_EVAL_METHOD_UNPREDICTABLE when "type" is
+	EXCESS_PRECISION_TYPE_STANDARD.
+	* target.def (excess_precision): Document that targets should
+	not return FLT_EVAL_METHOD_UNPREDICTABLE when "type" is
+	EXCESS_PRECISION_TYPE_STANDARD or EXCESS_PRECISION_TYPE_FAST.
+	Fix typo in first sentence.
+	* doc/tm.texi: Regenerate.
+
 2016-11-25  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/78396
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 0e8dda9..a96d597 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -51039,17 +51039,26 @@ ix86_excess_precision (enum excess_precision_type type)
       case EXCESS_PRECISION_TYPE_IMPLICIT:
 	/* Otherwise, the excess precision we want when we are
 	   in a standards compliant mode, and the implicit precision we
-	   provide can be identical.  */
+	   provide would be identical were it not for the unpredictable
+	   cases.  */
 	if (!TARGET_80387)
 	  return FLT_EVAL_METHOD_PROMOTE_TO_FLOAT;
-	else if (TARGET_MIX_SSE_I387)
-	  return FLT_EVAL_METHOD_UNPREDICTABLE;
-	else if (!TARGET_SSE_MATH)
-	  return FLT_EVAL_METHOD_PROMOTE_TO_LONG_DOUBLE;
-	else if (TARGET_SSE2)
-	  return FLT_EVAL_METHOD_PROMOTE_TO_FLOAT;
-	else
-	  return FLT_EVAL_METHOD_UNPREDICTABLE;
+	else if (!TARGET_MIX_SSE_I387)
+	  {
+	    if (!TARGET_SSE_MATH)
+	      return FLT_EVAL_METHOD_PROMOTE_TO_LONG_DOUBLE;
+	    else if (TARGET_SSE2)
+	      return FLT_EVAL_METHOD_PROMOTE_TO_FLOAT;
+	  }
+
+	/* If we are in standards compliant mode, but we know we will
+	   calculate in unpredictable precision, return
+	   FLT_EVAL_METHOD_FLOAT.  There is no reason to introduce explicit
+	   excess precision if the target can't guarantee it will honor
+	   it.  */
+	return (type == EXCESS_PRECISION_TYPE_STANDARD
+		? FLT_EVAL_METHOD_PROMOTE_TO_FLOAT
+		: FLT_EVAL_METHOD_UNPREDICTABLE);
       default:
 	gcc_unreachable ();
     }
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index bd82039..ebcadac 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -948,7 +948,7 @@ Do not define this macro if it would never modify @var{m}.
 @end defmac
 
 @deftypefn {Target Hook} {enum flt_eval_method} TARGET_C_EXCESS_PRECISION (enum excess_precision_type @var{type})
-Return a value, with the same meaning as @code{FLT_EVAL_METHOD} C that describes which excess precision should be applied.  @var{type} is either @code{EXCESS_PRECISION_TYPE_IMPLICIT}, @code{EXCESS_PRECISION_TYPE_FAST}, or @code{EXCESS_PRECISION_TYPE_STANDARD}.  For @code{EXCESS_PRECISION_TYPE_IMPLICIT}, the target should return which precision and range operations will be implictly evaluated in regardless of the excess precision explicitly added.  For @code{EXCESS_PRECISION_TYPE_STANDARD} and @code{EXCESS_PRECISION_TYPE_FAST}, the target should return the explicit excess precision that should be added depending on the value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{]}}.
+Return a value, with the same meaning as the C99 macro @code{FLT_EVAL_METHOD} that describes which excess precision should be applied.  @var{type} is either @code{EXCESS_PRECISION_TYPE_IMPLICIT}, @code{EXCESS_PRECISION_TYPE_FAST}, or @code{EXCESS_PRECISION_TYPE_STANDARD}.  For @code{EXCESS_PRECISION_TYPE_IMPLICIT}, the target should return which precision and range operations will be implictly evaluated in regardless of the excess precision explicitly added.  For @code{EXCESS_PRECISION_TYPE_STANDARD} and @code{EXCESS_PRECISION_TYPE_FAST}, the target should return the explicit excess precision that should be added depending on the value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{]}}. Note that unpredictable explicit excess precision does not make sense, so a target should never return @code{FLT_EVAL_METHOD_UNPREDICTABLE} when @var{type} is @code{EXCESS_PRECISION_TYPE_STANDARD} or @code{EXCESS_PRECISION_TYPE_FAST}.
 @end deftypefn
 
 @deftypefn {Target Hook} machine_mode TARGET_PROMOTE_FUNCTION_MODE (const_tree @var{type}, machine_mode @var{mode}, int *@var{punsignedp}, const_tree @var{funtype}, int @var{for_return})
diff --git a/gcc/target.def b/gcc/target.def
index efcc336..85a0ac0 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -5466,9 +5466,9 @@ DEFHOOK_UNDOC
 
 DEFHOOK
 (excess_precision,
- "Return a value, with the same meaning as @code{FLT_EVAL_METHOD} C that\
- describes which excess precision should be applied.  @var{type} is\
- either @code{EXCESS_PRECISION_TYPE_IMPLICIT},\
+ "Return a value, with the same meaning as the C99 macro\
+ @code{FLT_EVAL_METHOD} that describes which excess precision should be\
+ applied.  @var{type} is either @code{EXCESS_PRECISION_TYPE_IMPLICIT},\
  @code{EXCESS_PRECISION_TYPE_FAST}, or\
  @code{EXCESS_PRECISION_TYPE_STANDARD}.  For\
  @code{EXCESS_PRECISION_TYPE_IMPLICIT}, the target should return which\
@@ -5477,7 +5477,11 @@ DEFHOOK
  @code{EXCESS_PRECISION_TYPE_STANDARD} and\
  @code{EXCESS_PRECISION_TYPE_FAST}, the target should return the\
  explicit excess precision that should be added depending on the\
- value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{]}}.",
+ value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{]}}.\
+ Note that unpredictable explicit excess precision does not make sense,\
+ so a target should never return @code{FLT_EVAL_METHOD_UNPREDICTABLE}\
+ when @var{type} is @code{EXCESS_PRECISION_TYPE_STANDARD} or\
+ @code{EXCESS_PRECISION_TYPE_FAST}.",
  enum flt_eval_method, (enum excess_precision_type type),
  default_excess_precision)