Re: [RFC] [PATCH] Introduce configure flag --with-stage1-cflags.

["Martin Liška" <mliska@suse.cz>]

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On 05/26/2017 01:55 PM, Richard Biener wrote:
> On Fri, May 26, 2017 at 1:51 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>> On Fri, May 26, 2017 at 01:46:47PM +0200, Richard Biener wrote:
>>> On Thu, May 25, 2017 at 11:23 AM, Martin Liška <mliska@suse.cz> wrote:
>>>> Hello.
>>>>
>>>> After a discussion with Richi, using adding "-O2" to STAGE1 cflags with a recent
>>>> enough compiler can significantly speed up bootstrap. Thus I'm suggesting to
>>>> introduce --with-stage1-cflags where one can provide such options.
>>>
>>> I don't think this is necessary -- you can always override with STAGE1_CFLAGS.
>>>
>>>> Apart from that, maybe it would be handy to automatically enable "-O2" when
>>>> one has a recent compiler? Do we have an example where we detect host compiler
>>>> and it's version?
>>>
>>> Don't know about version but configury already detects that we use GCC, so that
>>> knowledge should be readily available.
>>
>> Well, it certainly shouldn't be -O2 by default for any system GCC, more
>> something like if it is major of the configured configure minus 1 or newer
>> (or minus 2?), then use -O2, otherwise default to -O0 as before.
> 
> I'd still default to -O0 on release branches regardless of version and then
> for development we can probably simply use "any GCC" when people have
> the chance to override.

Ok, sending new patch that does that on experimental branches for ${CC} --version
being a GCC newer than 4.9.

Martin

> 
> At least for me host GCC 4.8 works quite well with -O2.
> 
> Richard.
> 
>>         Jakub


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From 56acea8345eaa0961f12bfc2383c14676054665d Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Fri, 26 May 2017 14:58:39 +0200
Subject: [PATCH] Add -O2 to stage1_cflags for experimental branch.

ChangeLog:

2017-05-26  Martin Liska  <mliska@suse.cz>

	* configure.ac: Add -O2 to stage1_cflags for experimental branch.
	* configure: Regenerate.
---
 configure    | 23 +++++++++++++++++++++++
 configure.ac | 21 +++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/configure b/configure
index 82aa619fad1..079bad6bf34 100755
--- a/configure
+++ b/configure
@@ -7080,6 +7080,24 @@ fi
 $as_echo "$BUILD_CONFIG" >&6; }
 
 
+# Detect if compiler is GCC >= 4.8.x
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking CC is recent compiler" >&5
+$as_echo_n "checking CC is recent compiler... " >&6; }
+cc_is_recent_gcc=
+version_output=`${CC} -v 2>&1 | grep 'gcc version'`
+
+if test "x${version_output}" != x; then
+  version=`echo ${version_output} | sed 's/gcc version \([^ ]*\).*/\\1/'`
+  major=`echo ${version} | cut -d. -f1`
+  minor=`echo ${version} | cut -d. -f2`
+
+  if test "${major}" -ge 5 || ( test "${major}" -eq 4 && test "${minor}" -ge 8 ); then
+    cc_is_recent_gcc=yes
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $cc_is_recent_gcc" >&5
+$as_echo "$cc_is_recent_gcc" >&6; }
+
 # Use same top-level configure hooks in libgcc/libstdc++/libvtv.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --enable-vtable-verify" >&5
 $as_echo_n "checking for --enable-vtable-verify... " >&6; }
@@ -14655,6 +14673,11 @@ if test -d ${srcdir}/gcc && test x"`cat $srcdir/gcc/DEV-PHASE`" = xexperimental;
   "")
       stage2_werror_flag="--enable-werror-always" ;;
   esac
+
+  if test "$cc_is_recent_gcc" = "yes"; then
+    stage1_cflags="$stage1_cflags -O2"
+
+  fi
 fi
 
 
diff --git a/configure.ac b/configure.ac
index 78d2d593106..d312e2e8347 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2667,6 +2667,22 @@ fi
 AC_MSG_RESULT($BUILD_CONFIG)
 AC_SUBST(BUILD_CONFIG)
 
+# Detect if compiler is GCC >= 4.8.x
+AC_MSG_CHECKING(CC is recent compiler)
+cc_is_recent_gcc=
+version_output=`${CC} -v 2>&1 | grep 'gcc version'`
+
+if test "x${version_output}" != x; then
+  version=`echo ${version_output} | sed 's/gcc version \([[^ ]]*\).*/\\1/'`
+  major=`echo ${version} | cut -d. -f1`
+  minor=`echo ${version} | cut -d. -f2`
+
+  if test "${major}" -ge 5 || ( test "${major}" -eq 4 && test "${minor}" -ge 8 ); then
+    cc_is_recent_gcc=yes
+  fi
+fi
+AC_MSG_RESULT($cc_is_recent_gcc)
+
 # Use same top-level configure hooks in libgcc/libstdc++/libvtv.
 AC_MSG_CHECKING([for --enable-vtable-verify])
 AC_ARG_ENABLE(vtable-verify,
@@ -3521,6 +3537,11 @@ if test -d ${srcdir}/gcc && test x"`cat $srcdir/gcc/DEV-PHASE`" = xexperimental;
   "")
       stage2_werror_flag="--enable-werror-always" ;;
   esac
+
+  if test "$cc_is_recent_gcc" = "yes"; then
+    stage1_cflags="$stage1_cflags -O2"
+    AC_SUBST(stage1_cflags)
+  fi
 fi
 
 AC_SUBST(stage2_werror_flag)
-- 
2.12.2