Autoconf improvements

Added a __builtin_prefetch compiler check (which is basically there on
everything I've tried), and use this instead of SSE checks.

Also removed the needless ax_with_libdeflate.m4 which isn't used
anywhere.

Author: jkbonfield

configure.ac

@@ -109,6 +109,17 @@ unable to be decompressed and arith tests will fail.])
   fi
 fi
 
+dnl Check if __builtin_prefetch exists.
+AC_CACHE_CHECK([for __builtin_prefetch], [ax_cv_builtin_prefetch],[
+AC_LINK_IFELSE([AC_LANG_PROGRAM([], [__builtin_prefetch("")])],
+     [ax_cv_builtin_prefetch=yes],
+     [ax_cv_builtin_prefetch=no])
+])
+AS_IF([test "$ax_cv_builtin_prefetch" = "yes"],
+        [AC_DEFINE(HAVE_BUILTIN_PREFETCH, 1,
+           [Define to 1 if you have a __builtin_prefetch])],
+	[])
+
 dnl AC_CHECK_LIB([lzma], [lzma_easy_buffer_encode], [
 dnl 	LIBS="-llzma $LIBS"
 dnl 	AC_DEFINE([HAVE_LIBLZMA],1,[Define to 1 if you have the liblzma library.])])
@@ -220,8 +231,6 @@ AM_CONDITIONAL([RANS_32x16_AVX512],[test "$build_rans_avx512" = yes])
 
 AC_SUBST([HTSCODECS_SIMD_SRC])
 
-AX_LIBDEFLATE
-
 dnl Checks for header files.
 AC_HEADER_SYS_WAIT
 AC_CHECK_HEADERS(fcntl.h limits.h unistd.h malloc.h)

htscodecs/fqzcomp_qual.c

@@ -202,15 +202,14 @@ static int strat_opts[][12] = {
 };
 static int nstrats = sizeof(strat_opts) / sizeof(*strat_opts);
 
-#ifdef __SSE__
-#   include <xmmintrin.h>
-#   define _mm_prefetch2 _mm_prefetch
+#ifdef HAVE_BUILTIN_PREFETCH
+static inline void mm_prefetch(void *x) {
+    __builtin_prefetch(x);
+}
 #else
-#ifndef _MM_HINT_T0
-#define _MM_HINT_T0 0
-#endif
-static inline int _mm_prefetch2(void *x, int y) {
-    return *(volatile int *)x;
+static inline void mm_prefetch(void *x) {
+    // Fetch and discard is quite close to a genuine prefetch
+    *(volatile int *)x;
 }
 #endif
 
@@ -1119,19 +1118,19 @@ unsigned char *compress_block_fqz2f(int vers,
             // Model has symbols sorted by frequency, so most common are at
             // start.  So while model is approx 1Kb, the first cache line is
             // a big win.
-            _mm_prefetch2(&model.qual[l1], _MM_HINT_T0);
+            mm_prefetch(&model.qual[l1]);
             unsigned char qm1 = pm->qmap[in[i + ++j]];
             last = fqz_update_ctx(pm, &state, qm1); l2 = last;
 
-            _mm_prefetch2(&model.qual[l2], _MM_HINT_T0);
+            mm_prefetch(&model.qual[l2]);
             unsigned char qm2 = pm->qmap[in[i + ++j]];
             last = fqz_update_ctx(pm, &state, qm2); l3 = last;
 
-            _mm_prefetch2(&model.qual[l3], _MM_HINT_T0);
+            mm_prefetch(&model.qual[l3]);
             unsigned char qm3 = pm->qmap[in[i + ++j]];
             last = fqz_update_ctx(pm, &state, qm3); l4 = last;
 
-            _mm_prefetch2(&model.qual[l4], _MM_HINT_T0);
+            mm_prefetch(&model.qual[l4]);
             unsigned char qm4 = pm->qmap[in[i + ++j]];
             last = fqz_update_ctx(pm, &state, qm4);
 
@@ -1143,7 +1142,7 @@ unsigned char *compress_block_fqz2f(int vers,
 
         while (state.p > 0) {
             int l2 = last;
-            _mm_prefetch2(&model.qual[last], _MM_HINT_T0);
+            mm_prefetch(&model.qual[last]);
             unsigned char qm = pm->qmap[in[i + ++j]];
             last = fqz_update_ctx(pm, &state, qm);
             SIMPLE_MODEL(QMAX,_encodeSymbol)(&model.qual[l2], &rc, qm);