cmpbge emulation improvements

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Merge remote-tracking branch 'remotes/rth/tags/pull-axp-20150902' into staging

cmpbge emulation improvements

# gpg: Signature made Wed 02 Sep 2015 20:25:10 BST using RSA key ID 4DD0279B
# gpg: Good signature from "Richard Henderson <rth7680@gmail.com>"
# gpg:                 aka "Richard Henderson <rth@redhat.com>"
# gpg:                 aka "Richard Henderson <rth@twiddle.net>"

* remotes/rth/tags/pull-axp-20150902:
  target-alpha: Special case cmpbge with zero
  target-alpha: Rewrite helper_cmpbge using bit tests

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target-alpha/helper.h

@@ -10,6 +10,7 @@ DEF_HELPER_FLAGS_1(cttz, TCG_CALL_NO_RWG_SE, i64, i64)
 DEF_HELPER_FLAGS_2(zap, TCG_CALL_NO_RWG_SE, i64, i64, i64)
 DEF_HELPER_FLAGS_2(zapnot, TCG_CALL_NO_RWG_SE, i64, i64, i64)
 
+DEF_HELPER_FLAGS_1(cmpbe0, TCG_CALL_NO_RWG_SE, i64, i64)
 DEF_HELPER_FLAGS_2(cmpbge, TCG_CALL_NO_RWG_SE, i64, i64, i64)
 
 DEF_HELPER_FLAGS_2(minub8, TCG_CALL_NO_RWG_SE, i64, i64, i64)

target-alpha/int_helper.c

@@ -58,20 +58,47 @@ uint64_t helper_zap(uint64_t val, uint64_t mask)
     return helper_zapnot(val, ~mask);
 }
 
-uint64_t helper_cmpbge(uint64_t op1, uint64_t op2)
+uint64_t helper_cmpbe0(uint64_t a)
 {
-    uint8_t opa, opb, res;
+    uint64_t m = 0x7f7f7f7f7f7f7f7fULL;
-    int i;
+    uint64_t c = ~(((a & m) + m) | a | m);
+    /* a.......b.......c.......d.......e.......f.......g.......h....... */
+    c |= c << 7;
+    /* ab......bc......cd......de......ef......fg......gh......h....... */
+    c |= c << 14;
+    /* abcd....bcde....cdef....defg....efgh....fgh.....gh......h....... */
+    c |= c << 28;
+    /* abcdefghbcdefgh.cdefgh..defgh...efgh....fgh.....gh......h....... */
+    return c >> 56;
+}
 
-    res = 0;
+uint64_t helper_cmpbge(uint64_t a, uint64_t b)
-    for (i = 0; i < 8; i++) {
+{
-        opa = op1 >> (i * 8);
+    uint64_t mask = 0x00ff00ff00ff00ffULL;
-        opb = op2 >> (i * 8);
+    uint64_t test = 0x0100010001000100ULL;
-        if (opa >= opb) {
+    uint64_t al, ah, bl, bh, cl, ch;
-            res |= 1 << i;
+
-        }
+    /* Separate the bytes to avoid false positives.  */
-    }
+    al = a & mask;
-    return res;
+    bl = b & mask;
+    ah = (a >> 8) & mask;
+    bh = (b >> 8) & mask;
+
+    /* "Compare".  If a byte in B is greater than a byte in A,
+       it will clear the test bit.  */
+    cl = ((al | test) - bl) & test;
+    ch = ((ah | test) - bh) & test;
+
+    /* Fold all of the test bits into a contiguous set.  */
+    /* ch=.......a...............c...............e...............g........ */
+    /* cl=.......b...............d...............f...............h........ */
+    cl += ch << 1;
+    /* cl=......ab..............cd..............ef..............gh........ */
+    cl |= cl << 14;
+    /* cl=......abcd............cdef............efgh............gh........ */
+    cl |= cl << 28;
+    /* cl=......abcdefgh........cdefgh..........efgh............gh........ */
+    return cl >> 50;
 }
 
 uint64_t helper_minub8(uint64_t op1, uint64_t op2)

target-alpha/translate.c

@@ -1562,7 +1562,12 @@ static ExitStatus translate_one(DisasContext *ctx, uint32_t insn)
             break;
         case 0x0F:
             /* CMPBGE */
-            gen_helper_cmpbge(vc, va, vb);
+            if (ra == 31) {
+                /* Special case 0 >= X as X == 0.  */
+                gen_helper_cmpbe0(vc, vb);
+            } else {
+                gen_helper_cmpbge(vc, va, vb);
+            }
             break;
         case 0x12:
             /* S8ADDL */