[Qemu-devel] [PATCH 55/57] target-i386: Use clz/ctz for bsf/bsr helpers

[Richard Henderson]

And mark the helpers as NO_RWG_SE.

Signed-off-by: Richard Henderson <address@hidden>
---
 target-i386/helper.h     |  6 +++---
 target-i386/int_helper.c | 45 +++++++++++----------------------------------
 2 files changed, 14 insertions(+), 37 deletions(-)

diff --git a/target-i386/helper.h b/target-i386/helper.h
index 81e0fbd..e1ecdb8 100644
--- a/target-i386/helper.h
+++ b/target-i386/helper.h
@@ -195,9 +195,9 @@ DEF_HELPER_3(frstor, void, env, tl, int)
 DEF_HELPER_3(fxsave, void, env, tl, int)
 DEF_HELPER_3(fxrstor, void, env, tl, int)
 
-DEF_HELPER_1(bsf, tl, tl)
-DEF_HELPER_1(bsr, tl, tl)
-DEF_HELPER_2(lzcnt, tl, tl, int)
+DEF_HELPER_FLAGS_1(bsf, TCG_CALL_NO_RWG_SE, tl, tl)
+DEF_HELPER_FLAGS_1(bsr, TCG_CALL_NO_RWG_SE, tl, tl)
+DEF_HELPER_FLAGS_2(lzcnt, TCG_CALL_NO_RWG_SE, tl, tl, int)
 DEF_HELPER_FLAGS_2(pdep, TCG_CALL_NO_RWG_SE, tl, tl, tl)
 DEF_HELPER_FLAGS_2(pext, TCG_CALL_NO_RWG_SE, tl, tl, tl)
 
diff --git a/target-i386/int_helper.c b/target-i386/int_helper.c
index 527af40..7bec4eb 100644
--- a/target-i386/int_helper.c
+++ b/target-i386/int_helper.c
@@ -447,53 +447,30 @@ void helper_idivq_EAX(CPUX86State *env, target_ulong t0)
 }
 #endif
 
+#if TARGET_LONG_BITS == 32
+# define ctztl  ctz32
+# define clztl  clz32
+#else
+# define ctztl  ctz64
+# define clztl  clz64
+#endif
+
 /* bit operations */
 target_ulong helper_bsf(target_ulong t0)
 {
-    int count;
-    target_ulong res;
-
-    res = t0;
-    count = 0;
-    while ((res & 1) == 0) {
-        count++;
-        res >>= 1;
-    }
-    return count;
+    return ctztl(t0);
 }
 
 target_ulong helper_lzcnt(target_ulong t0, int wordsize)
 {
-    int count;
-    target_ulong res, mask;
-
-    if (wordsize > 0 && t0 == 0) {
-        return wordsize;
-    }
-    res = t0;
-    count = TARGET_LONG_BITS - 1;
-    mask = (target_ulong)1 << (TARGET_LONG_BITS - 1);
-    while ((res & mask) == 0) {
-        count--;
-        res <<= 1;
-    }
-    if (wordsize > 0) {
-        return wordsize - 1 - count;
-    }
-    return count;
+    return clztl(t0) - (TARGET_LONG_BITS - wordsize);
 }
 
 target_ulong helper_bsr(target_ulong t0)
 {
-    return helper_lzcnt(t0, 0);
+    return clztl(t0) ^ (TARGET_LONG_BITS - 1);
 }
 
-#if TARGET_LONG_BITS == 32
-# define ctztl  ctz32
-#else
-# define ctztl  ctz64
-#endif
-
 target_ulong helper_pdep(target_ulong src, target_ulong mask)
 {
     target_ulong dest = 0;
-- 
1.8.1.2