Re: -Wrestrict warning on cc 8.3.0

[Peter Stephenson <p.stephenson@xxxxxxxxxxx>]

On Wed, 2019-04-03 at 20:59 +0200, Wesley Schwengle wrote:
> During a make of the latest master I got the following warning:
> 
> gcc -c -I. -I../../Src -I../../Src -I../../Src/Zle -I.  -DHAVE_CONFIG_H
> -DMODULE -Wall -Wmissing-prototypes -O2 -fPIC -o compctl..o compctl.c
> compctl.c: In function ‘makecomplistflags.isra.6’:
> compctl.c:3340:7: warning: ‘strcpy’ accessing 1 byte at offsets [0,
> 9223372036854775807] and [0,9223372036854775807] may overlap 1 byte at
> offset 0 [-Wrestrict]
> strcpy(p, p + bl);
> ^~~~~~~~~~~~~~~~~
> rm -f compctl.so

This warning is thoroughly opaque --- and not occurring with a locally
compiled gcc 8.3.0 on my Ubuntu 16.04 64-bit Intel system --- but the
code isn't exactly crystal clear, either (subtracting a number off then
adding it immediately back on again isn't generally regarded as great
style), and it's quite possible the copy is overlapping.  Also, the last
person to worry about code optimisation in compctl emigrated to the
Undying Lands a decade ago (maybe I can still find the postcard...)

Can somebody verify the following is equivalent apart from dealing with
a possible overlapping copy?  I've no way of ensuring this code gets
exercised.

Separately, I seem to be having severe problems with --enable-zsh-mem
with that configuration.  It looked like some failed optimisation
involving realloc().  I think we had something similar a while ago?

Cheers
pws


diff --git a/Src/Zle/compctl.c b/Src/Zle/compctl.c
index fe87409..f963d57 100644
--- a/Src/Zle/compctl.c
+++ b/Src/Zle/compctl.c
@@ -3331,13 +3331,11 @@ makecomplistflags(Compctl cc, char *s, int incmd, int compadd)
 	    zlemetaline[end] = save;
 	    if (brend) {
 		Brinfo bp;
-		char *p;
-		int bl;
 
 		for (bp = brend; bp; bp = bp->next) {
-		    p = lpsuf + (we - zlemetacs) - bp->qpos -
-			(bl = strlen(bp->str));
-		    strcpy(p, p + bl);
+		    char *p2 = lpsuf + (we - zlemetacs) - bp->qpos;
+		    char *p1 = p2 - strlen(bp->str);
+		    memmove(p1, p2, strlen(p2) + 1);
 		}
 	    }
 	    if (!(lpsuf = strchr(lpsuf, '/')) && sf2)