[Qemu-devel] [PULL 2/2] target-alpha: Special case cmpbge with zero

[Richard Henderson <rth@twiddle.net>]

Knowing the comparator is zero leads to a simpler operation.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 target-alpha/helper.h     |  1 +
 target-alpha/int_helper.c | 14 ++++++++++++++
 target-alpha/translate.c  |  7 ++++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/target-alpha/helper.h b/target-alpha/helper.h
index d221f0d..83cbe2a 100644
--- a/target-alpha/helper.h
+++ b/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)
diff --git a/target-alpha/int_helper.c b/target-alpha/int_helper.c
index 4a6e955..d7f4774 100644
--- a/target-alpha/int_helper.c
+++ b/target-alpha/int_helper.c
@@ -58,6 +58,20 @@ uint64_t helper_zap(uint64_t val, uint64_t mask)
     return helper_zapnot(val, ~mask);
 }
 
+uint64_t helper_cmpbe0(uint64_t a)
+{
+    uint64_t m = 0x7f7f7f7f7f7f7f7fULL;
+    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;
+}
+
 uint64_t helper_cmpbge(uint64_t a, uint64_t b)
 {
     uint64_t mask = 0x00ff00ff00ff00ffULL;
diff --git a/target-alpha/translate.c b/target-alpha/translate.c
index 81d4ff8..b766ae3 100644
--- a/target-alpha/translate.c
+++ b/target-alpha/translate.c
@@ -1507,7 +1507,12 @@ 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 */
-- 
2.4.3