http://d.puremagic.com/issues/show_bug.cgi?id=2905

           Summary: [PATCH] Faster +-*/ involving a floating-pointing
                    literal
           Product: D
           Version: 2.029
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: patch, performance
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: clugdbug@yahoo.com.au


The front-end converts all floating-point literals into 80-bit real values, if they are specified either (1) with an L suffix, or (2) they are involved in an operation with a 'real'. It does this _even if the number could be represented as a double without loss of precision_. Unfortunately, the x87 can only do fused load-and-multiply, load-and-add, etc of float and double operands, so mixed-precision operations are a bit slower than they could be.

So, something like "x + 3.0" (where x is real), becomes:
static real THREE=3.0;
fld real ptr THREE;
faddp ST(1), ST;

and with this patch it becomes:
static double THREE=3.0;
fadd ST, double ptr THREE;

The patch is only applied in the case of +,-,*,/, so that something like
printf("%Lg", 2.0L);
will continue to work correctly.

The patch also includes the patch for 2888; they are very closely related.


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------- Comment #1 from clugdbug@yahoo.com.au  2009-04-27 07:57 -------
Created an attachment (id=342)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=342&action=view)
Patch against DMD2.029

Includes patch for 2888 as well.


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--- Comment #2 from Walter Bright <bugzilla@digitalmars.com>  2009-07-03 23:34:45 PDT ---
Created an attachment (id=412)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=412)
test program for fp patch

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--- Comment #3 from Walter Bright <bugzilla@digitalmars.com>  2009-07-03 23:36:52 PDT ---
The patch is incomplete, compile the test program with -O and it fails with an internal error. Haven't investigated why.

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--- Comment #4 from Don <clugdbug@yahoo.com.au>  2009-07-06 04:17:32 PDT ---
(In reply to comment #3)
> The patch is incomplete, compile the test program with -O and it fails with an internal error. Haven't investigated why.

OK, I'm on it.

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--- Comment #5 from Don <clugdbug@yahoo.com.au>  2009-07-06 04:54:46 PDT ---
This is a minimal case which ICEs with the patch. Order of terms in the expression is important.

void foo(real z) {}

void main (){
    real F = 1;
    foo( 1 + (F*3*2.1) );
}

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--- Comment #6 from Don <clugdbug@yahoo.com.au>  2009-07-10 07:37:23 PDT ---
Revised patch against DMD2.031, which fixes the problem, and optimises a larger number of cases. This patch significantly improves performance of floating-point operations involving reals.
----

Index: cg87.c ===================================================================
--- cg87.c    (revision 192)
+++ cg87.c    (working copy)
@@ -914,7 +914,8 @@
     case X(OPadd, TYdouble, TYdouble):
     case X(OPadd, TYdouble_alias, TYdouble_alias):
     case X(OPadd, TYldouble, TYldouble):
-//    case X(OPadd, TYldouble, TYdouble):
+    case X(OPadd, TYldouble, TYdouble):
+    case X(OPadd, TYdouble, TYldouble):
     case X(OPadd, TYifloat, TYifloat):
     case X(OPadd, TYidouble, TYidouble):
     case X(OPadd, TYildouble, TYildouble):
@@ -925,8 +926,8 @@
     case X(OPmin, TYdouble, TYdouble):
     case X(OPmin, TYdouble_alias, TYdouble_alias):
     case X(OPmin, TYldouble, TYldouble):
-//    case X(OPmin, TYldouble, TYdouble):
-//    case X(OPmin, TYdouble, TYldouble):
+    case X(OPmin, TYldouble, TYdouble):
+    case X(OPmin, TYdouble, TYldouble):
     case X(OPmin, TYifloat, TYifloat):
     case X(OPmin, TYidouble, TYidouble):
     case X(OPmin, TYildouble, TYildouble):
@@ -937,7 +938,8 @@
     case X(OPmul, TYdouble, TYdouble):
     case X(OPmul, TYdouble_alias, TYdouble_alias):
     case X(OPmul, TYldouble, TYldouble):
-//    case X(OPmul, TYldouble, TYdouble):
+    case X(OPmul, TYldouble, TYdouble):
+    case X(OPmul, TYdouble, TYldouble):
     case X(OPmul, TYifloat, TYifloat):
     case X(OPmul, TYidouble, TYidouble):
     case X(OPmul, TYildouble, TYildouble):
@@ -954,8 +956,8 @@
     case X(OPdiv, TYdouble, TYdouble):
     case X(OPdiv, TYdouble_alias, TYdouble_alias):
     case X(OPdiv, TYldouble, TYldouble):
-//    case X(OPdiv, TYldouble, TYdouble):
-//    case X(OPdiv, TYdouble, TYldouble):
+    case X(OPdiv, TYldouble, TYdouble):
+    case X(OPdiv, TYdouble, TYldouble):
     case X(OPdiv, TYifloat, TYifloat):
     case X(OPdiv, TYidouble, TYidouble):
     case X(OPdiv, TYildouble, TYildouble):
@@ -1364,7 +1366,12 @@
     #undef X

     e2oper = e2->Eoper;
-    if (e1->Eoper == OPconst ||
+    // Move double-sized operand into the second position if there's a chance
it will allow
+    // combining a load with an operation (DMD Bugzilla 2905)
+    if ( ((tybasic(e1->Ety)==TYdouble)
+          && ((e1->Eoper==OPvar) || (e1->Eoper==OPconst))
+          && (tybasic(e2->Ety) != TYdouble))
+    || (e1->Eoper == OPconst ) ||
     (e1->Eoper == OPvar &&
      ((e1->Ety & (mTYconst | mTYimmutable) && !OTleaf(e2oper)) ||
       (e2oper == OPd_f &&
Index: el.c
===================================================================
--- el.c    (revision 192)
+++ el.c    (working copy)
@@ -2052,7 +2052,6 @@
  * operations, since then it could change the type (eg, in the function call
  * printf("%La", 2.0L); the 2.0 must stay as a long double).
  */
-#if 0
 void shrinkLongDoubleConstantIfPossible(elem *e)
 {
     if (e->Eoper == OPconst && e->Ety == TYldouble)
@@ -2072,7 +2071,6 @@
     }
     }
 }
-#endif


 /*************************
@@ -2115,7 +2113,7 @@
          */
         break;
         }
-#if 0
+
     case OPdiv:
     case OPadd:
     case OPmin:
@@ -2125,7 +2123,6 @@
         if (tyreal(e->Ety))
         shrinkLongDoubleConstantIfPossible(e->E2);
         // fall through...
-#endif
     default:
         if (OTbinary(op))
         {

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> 2009-10-06 02:16:07 PDT ---
Fixed dmd 1.048 and 2.033

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