Re: [Emacs-diffs] master 6cd5678: Clarify compiler-pacifier in frame.c

[Paul Eggert <eggert@cs.ucla.edu>]

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Eli Zaretskii wrote:
> when geometry is non-zero, x and y are
> initialized.

And that means the initializations "x = 0, y = 0" were indeed unnecessary. The 
code works just fine without those initializations, because the values of x and 
y are not examined unless XParseGeometry has successfully set them.

Newer GCC is smart enough to figure this out, at least with the default 
optimizations. Other platforms evidently aren't smart enough.

> If we
> want this to be abundantly clear, we should have a comment there to
> the above effect.

Sure, I installed the attached.

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From 84f1674ee8cbd83ea219595e9adec2d148946976 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 24 Aug 2019 17:46:21 -0700
Subject: [PATCH] Clarify Fx_parse_geometry initialization
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* src/frame.c (Fx_parse_geometry): Clarify why local init
isn’t needed.
---
 src/frame.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/frame.c b/src/frame.c
index 330f98aee1..cf38c85f09 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -5327,9 +5327,10 @@ DEFUN ("x-parse-geometry", Fx_parse_geometry, Sx_parse_geometry, 1, 1, 0,
 On Nextstep, this just calls `ns-parse-geometry'.  */)
   (Lisp_Object string)
 {
-  int geometry, x UNINIT, y UNINIT;
+  /* x and y don't need initialization, as they are not accessed
+     unless XParseGeometry sets them.  */
+  int x UNINIT, y UNINIT;
   unsigned int width, height;
-  Lisp_Object result;
 
   CHECK_STRING (string);
 
@@ -5337,9 +5338,9 @@ DEFUN ("x-parse-geometry", Fx_parse_geometry, Sx_parse_geometry, 1, 1, 0,
   if (strchr (SSDATA (string), ' ') != NULL)
     return call1 (Qns_parse_geometry, string);
 #endif
-  geometry = XParseGeometry (SSDATA (string),
-			     &x, &y, &width, &height);
-  result = Qnil;
+  int geometry = XParseGeometry (SSDATA (string),
+				 &x, &y, &width, &height);
+  Lisp_Object result = Qnil;
   if (geometry & XValue)
     {
       Lisp_Object element;
-- 
2.17.1