[m-rev.] diff: always pass -fno-strict-aliasing to gcc

[Julien Fischer]

Avoid problems with GCC 4.3 and 4.4 on Linux.

configure.in:
 	Always use -fno-strict-aliasing if the C compiler type is GCC.
 	(Leaving this enabled causes GCC to apply optimizations that
 	will break in the presence of the type-punning that occurs in Mercury
 	generated C code.)

 	Remove the check for whether -fno-strict-aliasing is supported.
 	All versions of GCC that are usable with Mercury support it.

Julien.

Index: configure.in
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/configure.in,v
retrieving revision 1.557
diff -u -r1.557 configure.in
--- configure.in	15 Dec 2009 02:29:06 -0000	1.557
+++ configure.in	27 Dec 2009 17:59:14 -0000
@@ -810,35 +810,6 @@
      }
  EOF

-AC_MSG_CHECKING(whether we can use -fno-strict-aliasing)
-if $CC -O2 -Wall -fno-strict-aliasing -c conftest.c \
-    </dev/null >&AC_FD_CC 2>&1
-then
-    AC_MSG_RESULT(yes)
-
-    AC_MSG_CHECKING(whether we need to use -fno-strict-aliasing)
-    $CC -O2 -Wall -fno-strict-aliasing -c conftest.c \
-        </dev/null > conftest1.out 2>&1
-    $CC -O2 -Wall -c conftest.c \
-        </dev/null > conftest2.out 2>&1
-    # get the lines that exist only in conftest2.out
-    comm -13 conftest1.out conftest2.out > conftest.2only
-
-    if test -s conftest.2only
-    then
-        AC_MSG_RESULT(yes)
-        CFLAGS_FOR_NO_STRICT_ALIASING="-fno-strict-aliasing"
-    else
-        AC_MSG_RESULT(no)
-        CFLAGS_FOR_NO_STRICT_ALIASING=""
-    fi
-else
-    AC_MSG_RESULT(no)
-    CFLAGS_FOR_NO_STRICT_ALIASING=
-fi
-
-AC_SUBST(CFLAGS_FOR_NO_STRICT_ALIASING)
-
  AC_MSG_CHECKING(whether we can use -fno-move-loop-invariants)
  if $CC -fno-move-loop-invariants -c conftest.c \
      </dev/null >&AC_FD_CC 2>&1
@@ -4178,6 +4149,7 @@
      CFLAGS_FOR_WARNINGS="-Wall -Wwrite-strings -Wshadow -Wmissing-prototypes -Wno-unused -Wno-uninitialized -Wstrict-prototypes"
      CFLAGS_FOR_OPT="-O2 -fomit-frame-pointer"
      CFLAGS_FOR_DEBUG="-g"
+    CFLAGS_FOR_NO_STRICT_ALIASING="-fno-strict-aliasing"
      MCFLAGS_FOR_CC=
  else

@@ -4194,6 +4166,7 @@

              CFLAGS_FOR_OPT=
              CFLAGS_FOR_DEBUG="-g"
+            CFLAGS_FOR_NO_STRICT_ALIASING=
              MCFLAGS_FOR_CC=
              ;;

@@ -4203,6 +4176,7 @@
              CFLAGS_FOR_WARNINGS=
              CFLAGS_FOR_OPT=
              CFLAGS_FOR_DEBUG="/Zi"
+            CFLAGS_FOR_NO_STRICT_ALIASING=

              # Using the MSVC compiler implies that we must use
              # a maximum jump table size of 512 to avoid a fixed limit
@@ -4216,6 +4190,7 @@
              CFLAGS_FOR_OPT="-O"
              CFLAGS_FOR_WARNINGS=
              CFLAGS_FOR_DEBUG="-g"
+            CFLAGS_FOR_NO_STRICT_ALIASING=
              MCFLAGS_FOR_CC=
              ;;

@@ -4225,6 +4200,7 @@
              CFLAGS_FOR_OPT="-O"
              CFLAGS_FOR_WARNINGS=
              CFLAGS_FOR_DEBUG="-g"
+            CFLAGS_FOR_NO_STRICT_ALIASING=
              MCFLAGS_FOR_CC=
              ;;
      esac
@@ -4236,6 +4212,7 @@
  AC_SUBST([CFLAGS_FOR_WARNINGS])
  AC_SUBST([CFLAGS_FOR_OPT])
  AC_SUBST([CFLAGS_FOR_DEBUG])
+AC_SUBST([CFLAGS_FOR_NO_STRICT_ALIASING])
  AC_SUBST([MCFLAGS_FOR_CC])
  AC_SUBST([C_COMPILER_TYPE])


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