Re: Lilypond miscompiled on Fedora 17

[Pavel Roskin]

Quoting David Kastrup <address@hidden>:

> Now we just need to figure out which of the gazillion optimization
> options (listed in the assembly file) from O2 as compared to O1 makes
> the compilation go bad, and then we can add appropriate compiler
> options.
>
> We had to do this sort of $&!# already for gcc 4.6, so our configure
> tests are straightforward to fix once we know the option to switch off.

That's it:

`-ftree-vrp'
     Perform Value Range Propagation on trees.  This is similar to the
     constant propagation pass, but instead of values, ranges of values
     are propagated.  This allows the optimizers to remove unnecessary
     range checks like array bound checks and null pointer checks.
     This is enabled by default at `-O2' and higher.  Null pointer check
     elimination is only done if `-fdelete-null-pointer-checks' is
     enabled.

-fno-tree-vrp disables the optimization.

Here's the preliminary patch.  I'll submit it as an issue if you don't mind.


Add -fno-tree-vrp to CXXFLAGS for gcc 4.7.0

That optimization breaks min() call in simultaneous-music-iterator.cc
leading to bogus barcheck errors and incorrect output.
---
 stepmake/aclocal.m4 |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/stepmake/aclocal.m4 b/stepmake/aclocal.m4
index 8be2cab..42c65a5 100644
--- a/stepmake/aclocal.m4
+++ b/stepmake/aclocal.m4
@@ -287,12 +287,16 @@ AC_DEFUN(STEPMAKE_CXXTEMPLATE, [
 ])

 AC_DEFUN(STEPMAKE_GXXCODEGENBUG, [
-    AC_MSG_CHECKING([options for known g++ tail call bug])
+    AC_MSG_CHECKING([options for known g++ bugs])
     case "$GXX:$CXX_VERSION" in
        yes:400600?)
-           AC_MSG_RESULT([-fno-optimize-sibling-calls])
+           AC_MSG_RESULT([-fno-optimize-sibling-calls (tail call bug)])
            CXXFLAGS="$CXXFLAGS -fno-optimize-sibling-calls"
            ;;
+       yes:400700?)
+           AC_MSG_RESULT([-fno-tree-vrp (comparison bug)])
+           CXXFLAGS="$CXXFLAGS -fno-tree-vrp"
+           ;;
        *) AC_MSG_RESULT([none])
     esac
     AC_SUBST(CXXFLAGS)

--
Regards,
Pavel Roskin