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Add macros for diagnostic control, use them in locale/weightwc.h

Message ID 5475016C.8070805@cs.ucla.edu
State Committed
Headers show

Commit Message

Paul Eggert Nov. 25, 2014, 10:23 p.m. UTC
On 11/24/2014 04:00 PM, Roland McGrath wrote:
> The only thing I'd like you to do differently is to put more explanation in
> the code itself

Thanks, I installed the patch with that change.
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Patch

From 27f9b288f9af8ad7862c9852c4e002dbdf8207cc Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 25 Nov 2014 14:12:48 -0800
Subject: [PATCH] fnmatch: work around GCC compiler warning bug with uninit var

* posix/fnmatch_loop.c (FCT): Use a scalar not a one-item array.
This works around a bug with x86-64 GCC 4.9.2 and earlier
where 'gcc -O2 -Wmaybe-uninitialized' incorrectly complains
"../locale/weightwc.h:93:7: warning: '*((void *)&str+4)' may be
used uninitialized in this function [-Wmaybe-uninitialized]".
---
 ChangeLog            |  9 +++++++++
 posix/fnmatch_loop.c | 13 +++++++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 8ee0650..c020ed4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@ 
+2014-11-25  Paul Eggert  <eggert@cs.ucla.edu>
+
+	fnmatch: work around GCC compiler warning bug with uninit var
+	* posix/fnmatch_loop.c (FCT): Use a scalar not a one-item array.
+	This works around a bug with x86-64 GCC 4.9.2 and earlier
+	where 'gcc -O2 -Wmaybe-uninitialized' incorrectly complains
+	"../locale/weightwc.h:93:7: warning: '*((void *)&str+4)' may be
+	used uninitialized in this function [-Wmaybe-uninitialized]".
+
 2014-11-25  Joseph Myers  <joseph@codesourcery.com>
 
 	* posix/bug-regex31.c (main): Return RES not 0.
diff --git a/posix/fnmatch_loop.c b/posix/fnmatch_loop.c
index db6d9d7..1e27913 100644
--- a/posix/fnmatch_loop.c
+++ b/posix/fnmatch_loop.c
@@ -343,7 +343,12 @@  FCT (pattern, string, string_end, no_leading_period, flags, ends, alloca_used)
 #ifdef _LIBC
 		else if (c == L('[') && *p == L('='))
 		  {
-		    UCHAR str[1];
+		    /* It's important that STR be a scalar variable rather
+		       than a one-element array, because GCC (at least 4.9.2
+		       -O2 on x86-64) can be confused by the array and
+		       diagnose a "used initialized" in a dead branch in the
+		       findidx function.  */
+		    UCHAR str;
 		    uint32_t nrules =
 		      _NL_CURRENT_WORD (LC_COLLATE, _NL_COLLATE_NRULES);
 		    const CHAR *startp = p;
@@ -355,7 +360,7 @@  FCT (pattern, string, string_end, no_leading_period, flags, ends, alloca_used)
 			c = L('[');
 			goto normal_bracket;
 		      }
-		    str[0] = c;
+		    str = c;
 
 		    c = *++p;
 		    if (c != L('=') || p[1] != L(']'))
@@ -368,7 +373,7 @@  FCT (pattern, string, string_end, no_leading_period, flags, ends, alloca_used)
 
 		    if (nrules == 0)
 		      {
-			if ((UCHAR) *n == str[0])
+			if ((UCHAR) *n == str)
 			  goto matched;
 		      }
 		    else
@@ -383,7 +388,7 @@  FCT (pattern, string, string_end, no_leading_period, flags, ends, alloca_used)
 # endif
 			const int32_t *indirect;
 			int32_t idx;
-			const UCHAR *cp = (const UCHAR *) str;
+			const UCHAR *cp = (const UCHAR *) &str;
 
 # if WIDE_CHAR_VERSION
 			table = (const int32_t *)
-- 
1.9.3