+
+dnl 'make compare' can be significantly faster, if cmp itself can
+dnl skip bytes instead of using tail. The test being performed is
+dnl "if cmp --ignore-initial=2 t1 t2 && ! cmp --ignore-initial=1 t1 t2"
+dnl but we need to sink errors and handle broken shells. We also test
+dnl for the parameter format "cmp file1 file2 skip1 skip2" which is
+dnl accepted by cmp on some systems.
+AC_DEFUN([ACX_PROG_CMP_IGNORE_INITIAL],
+[AC_CACHE_CHECK([how to compare bootstrapped objects], gcc_cv_prog_cmp_skip,
+[ echo abfoo >t1
+ echo cdfoo >t2
+ gcc_cv_prog_cmp_skip='tail +16c $$f1 > tmp-foo1; tail +16c $$f2 > tmp-foo2; cmp tmp-foo1 tmp-foo2'
+ if cmp t1 t2 2 2 > /dev/null 2>&1; then
+ if cmp t1 t2 1 1 > /dev/null 2>&1; then
+ :
+ else
+ gcc_cv_prog_cmp_skip='cmp $$f1 $$f2 16 16'
+ fi
+ fi
+ if cmp --ignore-initial=2 t1 t2 > /dev/null 2>&1; then
+ if cmp --ignore-initial=1 t1 t2 > /dev/null 2>&1; then
+ :
+ else
+ gcc_cv_prog_cmp_skip='cmp --ignore-initial=16 $$f1 $$f2'
+ fi
+ fi
+ rm t1 t2
+])
+do_compare="$gcc_cv_prog_cmp_skip"
+AC_SUBST(do_compare)
+])