From 2e1df1dc78f38e04908abe1b26cd68953572e424 Mon Sep 17 00:00:00 2001
From: Kalle Olavi Niemitalo <kon@iki.fi>
Date: Sun, 4 May 2008 11:20:55 +0300
Subject: [PATCH] Bug 1012: Compile with -fno-strict-overflow or -fwrapv.
 (cherry picked from commit b7312e6882ab9a1792ac8e082bdb7aae6971cae1)

---
 NEWS         |  1 +
 configure.in | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/NEWS b/NEWS
index 9b68f4f4..9165b2aa 100644
--- a/NEWS
+++ b/NEWS
@@ -323,6 +323,7 @@ To be released as 0.11.4.
 * bug 938: elinks -remote no longer needs a controlling tty
 * bug 939: fix FSP directory listing (some compiler options left it empty)
 * bug 978: Python's webbrowser.open_new_tab(URL) works since now
+* bug 1012: compile with -fno-strict-overflow or -fwrapv if available
 * minor bug 54, Debian bug 338402: don't force the terminal to 8 bits
   with no parity, and don't disable XON/XOFF flow control either
 * minor bug 951 in user SMJS: garbage-collect SMJS objects on 'File ->
diff --git a/configure.in b/configure.in
index d32ca56a..7d32730f 100644
--- a/configure.in
+++ b/configure.in
@@ -1451,6 +1451,61 @@ if test "x$ac_cv_c_compiler_gnu" = "xyes"; then
       [AC_MSG_RESULT([no])])
     EL_RESTORE_FLAGS
   done
+
+  # Bug 1012: Some parts of ELinks do arithmetic with signed integers
+  # in such a way that an overflow is possible.  GCC 4.2.1 warns
+  # "warning: assuming signed overflow does not occur when assuming
+  # that (X + c) > X is always true", which may be an incorrect
+  # optimization (although allowed by the standard), and breaks the
+  # build with -Werror.
+  #
+  # All of the following tests included -S -Wall -Wextra:
+  #
+  # GCC: (GNU) 4.0.4 20060507 (prerelease) (Debian 4.0.3-3)
+  # * gcc-4.0 -O0: OK, compares the values
+  # * gcc-4.0 -O2: assumes no overflow, does not warn
+  # * gcc-4.0 -O0 -fno-strict-overflow: unrecognized command line option
+  # * gcc-4.0 -O0 -fwrapv: OK, compares the values
+  # * gcc-4.0 -O2 -fwrapv: OK, compares the values
+  # * gcc-4.0 -O0 -ftrapv: OK, calls __addvsi3
+  # * gcc-4.0 -O2 -ftrapv: assumes no overflow, does not warn
+  # * gcc-4.0 -O0 -fwrapv -ftrapv: OK, calls __addvsi3
+  # * gcc-4.0 -O2 -fwrapv -ftrapv: compares the values
+  #
+  # GCC: (GNU) 4.1.3 20070812 (prerelease) (Debian 4.1.2-15)
+  # * gcc-4.1 -O0: assumes no overflow, does not warn
+  # * gcc-4.1 -O2: assumes no overflow, does not warn
+  # * gcc-4.1 -O0 -fno-strict-overflow: unrecognized command line option
+  # * gcc-4.1 -O0 -fwrapv: OK, compares the values
+  # * gcc-4.1 -O2 -fwrapv: OK, compares the values
+  # * gcc-4.1 -O0 -ftrapv: OK, calls __addvsi3
+  # * gcc-4.1 -O2 -ftrapv: compares the values
+  # * gcc-4.1 -O0 -fwrapv -ftrapv: OK, calls __addvsi3
+  # * gcc-4.1 -O2 -fwrapv -ftrapv: compares the values
+  #
+  # GCC: (GNU) 4.2.1 (Debian 4.2.1-5)
+  # * gcc-4.2 -O0: OK, compares the values
+  # * gcc-4.2 -O2: assumes no overflow, warns about it
+  # * gcc-4.2 -O0 -fno-strict-overflow: OK, compares the values
+  # * gcc-4.2 -O2 -fno-strict-overflow: OK, compares the values
+  # * gcc-4.2 -O0 -fwrapv: OK, compares the values
+  # * gcc-4.2 -O2 -fwrapv: OK, compares the values
+  # * gcc-4.2 -O0 -ftrapv: OK, calls __addvsi3
+  # * gcc-4.2 -O2 -ftrapv: compares the values
+  # * gcc-4.2 -O0 -fwrapv -ftrapv: OK, calls __addvsi3
+  # * gcc-4.2 -O2 -fwrapv -ftrapv: compares the values
+  #
+  # Apparently, -ftrapv does not work reliably at all.
+  for overflow_flag in -fno-strict-overflow -fwrapv; do
+    AC_MSG_CHECKING([whether $CC accepts $overflow_flag])
+    EL_SAVE_FLAGS
+    CFLAGS="$CFLAGS $overflow_flag"
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
+      [AC_MSG_RESULT([yes])
+       break],
+      [AC_MSG_RESULT([no])])
+    EL_RESTORE_FLAGS
+  done
 fi
 
 EL_LOG_CONFIG(CFLAGS, [Compiler flags (CFLAGS)], [])