[Bug d/96429] New: d: Pointer subtraction uses TRUNC_DIV_EXPR

[Bug d/96429] New: d: Pointer subtraction uses TRUNC_DIV_EXPR

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96429

            Bug ID: 96429
           Summary: d: Pointer subtraction uses TRUNC_DIV_EXPR
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: ibuclaw at gdcproject dot org
  Target Milestone: ---

Given the pointer operation:

    long delta = smaller & (read - first);

This gets lowered as (-fdump-tree-original)

    long delta = (long) smaller & (read - first) / 8;

Instead of...

    long delta = (long) smaller & (read - first) /[ex] 8;

Switching will likely give some marginal gains on performance.

[Bug d/96429] d: Pointer subtraction uses TRUNC_DIV_EXPR

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96429

--- Comment #1 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
--- a/gcc/d/expr.cc
+++ b/gcc/d/expr.cc
@@ -620,6 +620,18 @@ public:
        break;

       case TOKdiv:
+       /* Determine if the div expression is a lowered pointer diff operation.
+          The front-end rewrites `(p1 - p2)' into `(p1 - p2) / stride'.  */
+       if (MinExp *me = e->e1->isMinExp ())
+         {
+           if (me->e1->type->ty == Tpointer && me->e2->type->ty == Tpointer
+               && e->e2->op == TOKint64)
+             {
+               code = EXACT_DIV_EXPR;
+               break;
+             }
+         }
+
        code = e->e1->type->isintegral ()
          ? TRUNC_DIV_EXPR : RDIV_EXPR;
        break;

[Bug d/96429] d: Pointer subtraction uses TRUNC_DIV_EXPR

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96429

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Iain Buclaw <ibuclaw@gcc.gnu.org>:

https://gcc.gnu.org/g:3a3fda119036f46bfa70e06e7c69e04e78040079

commit r11-2536-g3a3fda119036f46bfa70e06e7c69e04e78040079
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Mon Aug 3 22:35:38 2020 +0200

    d: Fix PR96429: Pointer subtraction uses TRUNC_DIV_EXPR

    gcc/d/ChangeLog:

            PR d/96429
            * expr.cc (ExprVisitor::visit (BinExp*)): Use EXACT_DIV_EXPR for
            pointer diff expressions.

    gcc/testsuite/ChangeLog:

            PR d/96429
            * gdc.dg/pr96429.d: New test.

[Bug d/96429] d: Pointer subtraction uses TRUNC_DIV_EXPR

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96429

Iain Buclaw <ibuclaw at gdcproject dot org> changed:

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

--- Comment #3 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
Fixed.