Allow to disable optimizations for portability

We're having trouble on Fedora when the build system runs
on Intel CPUs. The ./configure detects AVX instructions and
builds liberasurecode with them. The resulting library crashes
with SIGILL when users run it on ADM CPUs without AVX.

See the details here:
 https://bugzilla.redhat.com/show_bug.cgi?id=1454543

The patch allows to disable the optimizations, so that
distro packaging then can invoke this options and build
portable libraries.

For the record, "make test" runs about 16% slower on an Intel
CPU if optimizations are disabled. So, there's a measurable
performance impact. However, operators intersted in outright
performance might want to consider Erasure Coding implementations
other than the one  built-in into liberasurecode. The library
supports other back-ends that are significantly faster than
even optimized built-in code.

Change-Id: I09603b97ceeb833ba582cf3217e0be51c019d645

1 files changed, 73 insertions, 60 deletions

diff --git a/configure.ac b/configure.ac
index c3509d2..69df9a3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -151,68 +151,81 @@ AC_SUBST(ac_aux_dir)
 AC_SUBST(OBJECTS)
 
 dnl Do CPUID and associated compiler flag checks
+dnl but allow to disable all of this in order to build portable binaries
 
-SUPPORTED_FLAGS=""
-$CC - -E -mmmx </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="-mmmx"
-  AC_MSG_RESULT([$CC supports -mmmx])
-fi
-$CC - -E -msse </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse"
-  AC_MSG_RESULT([$CC supports -msse])
-fi
-$CC - -E -msse2 </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse2"
-  AC_MSG_RESULT([$CC supports -msse2])
-fi
-$CC - -E -msse3 </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse3"
-  AC_MSG_RESULT([$CC supports -msse3])
-fi
-$CC - -E -mssse3 </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -mssse3"
-  AC_MSG_RESULT([$CC supports -mssse3])
-fi
-$CC - -E -msse4.1 </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse4.1"
-  AC_MSG_RESULT([$CC supports -msse4.1])
-fi
-$CC - -E -msse4.2 </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse4.2"
-  AC_MSG_RESULT([$CC supports -msse4.2])
-fi
-$CC - -E -mavx </dev/null >/dev/null 2>&1
-if [[ $? == "0" ]]; then
-  SUPPORTED_FLAGS="$SUPPORTED_FLAGS -mavx"
-  AC_MSG_RESULT([$CC supports -mavx])
-fi
+AC_ARG_ENABLE([mmi], [  --disable-mmi           do not use host-specific instructions],
+[case "${enableval}" in
+    yes) mmi=true ;;
+    no)  mmi=false ;;
+    *) AC_MSG_ERROR([bad value ${enableval} for --disable-mmi]) ;;
+esac],[mmi=true])
+
+if test x$mmi = xtrue ; then
+
+    SUPPORTED_FLAGS=""
+    $CC - -E -mmmx </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="-mmmx"
+      AC_MSG_RESULT([$CC supports -mmmx])
+    fi
+    $CC - -E -msse </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse"
+      AC_MSG_RESULT([$CC supports -msse])
+    fi
+    $CC - -E -msse2 </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse2"
+      AC_MSG_RESULT([$CC supports -msse2])
+    fi
+    $CC - -E -msse3 </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse3"
+      AC_MSG_RESULT([$CC supports -msse3])
+    fi
+    $CC - -E -mssse3 </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -mssse3"
+      AC_MSG_RESULT([$CC supports -mssse3])
+    fi
+    $CC - -E -msse4.1 </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse4.1"
+      AC_MSG_RESULT([$CC supports -msse4.1])
+    fi
+    $CC - -E -msse4.2 </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -msse4.2"
+      AC_MSG_RESULT([$CC supports -msse4.2])
+    fi
+    $CC - -E -mavx </dev/null >/dev/null 2>&1
+    if [[ $? == "0" ]]; then
+      SUPPORTED_FLAGS="$SUPPORTED_FLAGS -mavx"
+      AC_MSG_RESULT([$CC supports -mavx])
+    fi
 
-# Detect the SIMD features supported by both the compiler and the CPU
-SIMD_FLAGS=""
-cat "$srcdir/get_flags_from_cpuid.c" \
-    | sed "s/FLAGSFROMAUTOCONF/${SUPPORTED_FLAGS}/" \
-    | $CC -x c -g - -o get_flags_from_cpuid
-if [[ -e ./get_flags_from_cpuid ]]; then
-  chmod 755 get_flags_from_cpuid; ./get_flags_from_cpuid; rm ./get_flags_from_cpuid
-  if [[ -e compiler_flags ]]; then
-    SIMD_FLAGS=`cat compiler_flags`
-    rm -f compiler_flags
-  else
-    AC_MSG_WARN([Could not run the CPUID detection program])
-  fi
-else
-  AC_MSG_WARN([Could not compile the CPUID detection program])
-fi
+    # Detect the SIMD features supported by both the compiler and the CPU
+    SIMD_FLAGS=""
+    cat "$srcdir/get_flags_from_cpuid.c" \
+        | sed "s/FLAGSFROMAUTOCONF/${SUPPORTED_FLAGS}/" \
+        | $CC -x c -g - -o get_flags_from_cpuid
+    if [[ -e ./get_flags_from_cpuid ]]; then
+      chmod 755 get_flags_from_cpuid
+      ./get_flags_from_cpuid
+      rm ./get_flags_from_cpuid
+      if [[ -e compiler_flags ]]; then
+        SIMD_FLAGS=`cat compiler_flags`
+        rm -f compiler_flags
+      else
+        AC_MSG_WARN([Could not run the CPUID detection program])
+      fi
+    else
+      AC_MSG_WARN([Could not compile the CPUID detection program])
+    fi
 
-AC_MSG_RESULT([Generating with SIMD flags: $SIMD_FLAGS])
-CFLAGS="$CFLAGS $SIMD_FLAGS"
+    AC_MSG_RESULT([Generating with SIMD flags: $SIMD_FLAGS])
+    CFLAGS="$CFLAGS $SIMD_FLAGS"
+fi
 
 # Certain code may be dependent on 32 vs. 64-bit arch, so add a 
 # flag for 64-bit
@@ -231,7 +244,7 @@ AM_CONDITIONAL(HAVE_DOXYGEN, $DOXYGEN)
 AC_SUBST(HAVE_DOXYGEN)
 
 dnl Let people disable the doxygen stuff.
-AC_ARG_ENABLE(doxygen, [  --enable-doxygen         Use doxygen to build documentation (default=auto)],
+AC_ARG_ENABLE(doxygen, [  --enable-doxygen        use doxygen to build documentation (default=auto)],
     enable_doxygen="$enableval",
     enable_doxygen=auto)