makefile: Automatically optimize for your machine

Setting the makefile variable AUTO_OPT_GCC will give GCC a list of
optimization flags suited for the machine make is run on. It does this
using util/auto-opt.sh.  "-march=native -mtune=native" are always
outputted, which causes GCC to detect the CPU type you use and generate
code for that.  On Linux systems it also looks at the flags line of
/proc/cpuinfo to pick x86 optimization flags.

1 files changed, 50 insertions, 0 deletions

diff --git a/crawl-ref/source/util/auto-opt.sh b/crawl-ref/source/util/auto-opt.sh
new file mode 100755
index 0000000000..8f4aa185cb
--- /dev/null
+++ b/crawl-ref/source/util/auto-opt.sh
@@ -0,0 +1,50 @@
+#!/bin/bash --noprofile
+
+#########################################################################
+# Called by the makefile if AUTO_OPT_GCC is true, outputs the list of CPU
+# specific optimization flags that should be used.
+#########################################################################
+
+#TODO: Detect extra compiler options for:
+#
+# * Non-gcc compilers.
+# * CYGWIN.
+# * Mac OS X.
+# * Non-x86 Linux systems.
+
+#########################################################################
+
+# This line makes GCC automatically detect the CPU architecture to use.  Also
+# might cause the use of some of the "-m" options we use down below,
+# but GCC doesn't complain about an "-m" option being used repeatedly.
+OUT="-mtune=native -march=native"
+
+if [ -f /proc/cpuinfo ]; then
+    # On Linux system, the "flags: " line of /proc/cpuinfo indicates which
+    # extended instruction sets are available (among other things), so we
+    # can use that to detect what to use.
+
+    # Only get info for the first CPU; assumes that all CPUs in the system
+    # are the same
+    INFO=`cat /proc/cpuinfo | grep '^flags.*:' | head -n 1`
+
+    # These are currently all x86 specific.
+    for flag in cx16 mmx sse sse2 sse3 sse4.1 sse4.2 sse4 sse4a 3dnow abm; do
+        # Put a space on either side of the flag name, so that it won't
+        # match in the middle of a flag.
+        if [[ $INFO == *\ $flag\ * ]] ; then
+            OUT="$OUT -m$flag"
+        fi
+    done
+
+    if [[ $INFO == *\ lahf_lm\ * ]]; then
+        OUT="$OUT -msahf"
+    fi
+
+    # Any available SSE lets us use -mfpmath=sse
+    if [[ $INFO == *\ sse* ]]; then
+        OUT="$OUT -mfpmath=sse"
+    fi
+fi
+
+echo "$OUT"