[LLVMbugs] [Bug 16724] New: configure script errors in llvm-3.3 and current trunk cause --enable-optimize to not be used and instead continue to use CFLAGS set by build environment

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16724

            Bug ID: 16724
           Summary: configure script errors in llvm-3.3 and current trunk
                    cause --enable-optimize to not be used and instead
                    continue to use CFLAGS set by build environment
           Product: Build scripts
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: autoconf
          Assignee: unassignedbugs at nondot.org
          Reporter: jeremyhu at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Found downstream: https://trac.macports.org/ticket/39761

If you set CFLAGS="-O2 -pipe" when configuring llvm, you'll see something like:
./configure: line 1990: -O2: command not found
./configure: line 1991: -O2: command not found

And -O2 will be preferred over the value passed to --enable-optimize

Those lines of the configure script are just:
${CFLAGS=}
${CXXFLAGS=}

which come from this in configure.ac:

dnl Default to empty (i.e. assigning the null string to) CFLAGS and CXXFLAGS,
dnl instead of the autoconf default (for example, '-g -O2' for CC=gcc).
${CFLAGS=}
${CXXFLAGS=}

which was a bug introduced by this commit:

commit 6c440fcea52e27b3befcf2ad5f7dcc58a15a2e58
Author: Patrik Hagglund <patrik.h.hagglund at ericsson.com>
Date:   Mon Feb 4 08:15:53 2013 +0000

    Pass CPPFLAGS/CFLAGS/CXXFLAGS from the environment of configure to
    Makefile.config.

    This is implied at the bottom of the help text of configure (besides
    CC/CXX/LDFLAGS, already passed to Makefile.config).

    For backward compatibility, the values of CFLAGS and CXXFLAGS defaults
    to empty, overriding the default values provided by autoconf (for
    example, '-g -O2' when CC=gcc').

    $(CPP) is not used by our makefiles. Therefore, the value of CPP is
    not passed to Makefile.config, despite beeing mentioned by 'configure
    --help'.

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174313
91177308-0d34-0410-b5e6-96231b3b80d8

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