Re: [Qemu-devel] Mips 64 emulation not compiling

[Thiemo Seufer <ths@networkno.de>]

J. Mayer wrote:
> The latest patches in clo makes gcc 3.4.6 fail to build the mips64
> targets on my amd64 host (looks like an register allocation clash in the
> optimizer code).

Your version is likely faster as well.

> Furthermore, the clz micro-op for Mips seems very suspect to me,
> according to the changes made in the clo implementation.

It is correct, the sign-extension are zero in that case.

> I did change the clz / clo implementation to use the same code as the
> one used for the PowerPC implementation. It seems to me that the result
> would be correct... And it compiles...
> 
> Please take a look to the folowing patch:

We have now clz/clo in several places, so I expanded your patch a
bit. For now it is only used for the mips target. Comments?


Thiemo


Index: qemu-work/host-utils.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ qemu-work/host-utils.h	2007-10-27 12:13:30.000000000 +0100
@@ -0,0 +1,104 @@
+/*
+ * Utility compute operations used by translated code.
+ *
+ * Copyright (c) 2007 Thiemo Seufer
+ * Copyright (c) 2007 Jocelyn Mayer
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/* Note that some of those functions may end up calling libgcc functions,
+   depending on the host machine. It is up to the target emulation to
+   cope with that. */
+
+/* Binary search for leading zeros.  */
+
+static always_inline int clz32(uint32_t val)
+{
+    int cnt = 0;
+
+    if (!(val & 0xFFFF0000U)) {
+        cnt += 16;
+        val <<= 16;
+    }
+    if (!(val & 0xFF000000U)) {
+        cnt += 8;
+        val <<= 8;
+    }
+    if (!(val & 0xF0000000U)) {
+        cnt += 4;
+        val <<= 4;
+    }
+    if (!(val & 0xC0000000U)) {
+        cnt += 2;
+        val <<= 2;
+    }
+    if (!(val & 0x80000000U)) {
+        cnt++;
+        val <<= 1;
+    }
+    if (!(val & 0x80000000U)) {
+        cnt++;
+    }
+    return cnt;
+}
+
+static always_inline int clo32(uint32_t val)
+{
+    return clz32(~val);
+}
+
+static always_inline int clz64(uint64_t val)
+{
+    int cnt = 0;
+
+    if (!(val & 0xFFFFFFFF00000000ULL)) {
+        cnt += 32;
+        val <<= 32;
+    }
+    if (!(val & 0xFFFF000000000000ULL)) {
+        cnt += 16;
+        val <<= 16;
+    }
+    if (!(val & 0xFF00000000000000ULL)) {
+        cnt += 8;
+        val <<= 8;
+    }
+    if (!(val & 0xF000000000000000ULL)) {
+        cnt += 4;
+        val <<= 4;
+    }
+    if (!(val & 0xC000000000000000ULL)) {
+        cnt += 2;
+        val <<= 2;
+    }
+    if (!(val & 0x8000000000000000ULL)) {
+        cnt++;
+        val <<= 1;
+    }
+    if (!(val & 0x8000000000000000ULL)) {
+        cnt++;
+    }
+    return cnt;
+}
+
+static always_inline int clo64(uint64_t val)
+{
+    return clz64(~val);
+}
Index: qemu-work/target-mips/exec.h
===================================================================
--- qemu-work.orig/target-mips/exec.h	2007-10-26 22:42:15.000000000 +0100
+++ qemu-work/target-mips/exec.h	2007-10-27 12:13:30.000000000 +0100
@@ -70,6 +70,8 @@
 void do_dsrav (void);
 void do_dsrlv (void);
 void do_drotrv (void);
+void do_dclo (void);
+void do_dclz (void);
 #endif
 #endif
 
Index: qemu-work/target-mips/op.c
===================================================================
--- qemu-work.orig/target-mips/op.c	2007-10-26 22:42:14.000000000 +0100
+++ qemu-work/target-mips/op.c	2007-10-27 12:13:30.000000000 +0100
@@ -22,6 +22,7 @@
 
 #include "config.h"
 #include "exec.h"
+#include "host-utils.h"
 
 #ifndef CALL_FROM_TB0
 #define CALL_FROM_TB0(func) func()
@@ -537,35 +538,13 @@
 
 void op_clo (void)
 {
-    int n;
-
-    if (T0 == ~((target_ulong)0)) {
-        T0 = 32;
-    } else {
-        for (n = 0; n < 32; n++) {
-            if (!(((int32_t)T0) & (1 << 31)))
-                break;
-            T0 <<= 1;
-        }
-        T0 = n;
-    }
+    T0 = clo32(T0);
     RETURN();
 }
 
 void op_clz (void)
 {
-    int n;
-
-    if (T0 == 0) {
-        T0 = 32;
-    } else {
-        for (n = 0; n < 32; n++) {
-            if (T0 & (1 << 31))
-                break;
-            T0 <<= 1;
-        }
-        T0 = n;
-    }
+    T0 = clz32(T0);
     RETURN();
 }
 
@@ -645,6 +624,18 @@
     RETURN();
 }
 
+void op_dclo (void)
+{
+    CALL_FROM_TB0(do_dclo);
+    RETURN();
+}
+
+void op_dclz (void)
+{
+    CALL_FROM_TB0(do_dclz);
+    RETURN();
+}
+
 #else /* TARGET_LONG_BITS > HOST_LONG_BITS */
 
 void op_dsll (void)
@@ -735,41 +726,19 @@
        T0 = T1;
     RETURN();
 }
-#endif /* TARGET_LONG_BITS > HOST_LONG_BITS */
 
 void op_dclo (void)
 {
-    int n;
-
-    if (T0 == ~((target_ulong)0)) {
-        T0 = 64;
-    } else {
-        for (n = 0; n < 64; n++) {
-            if (!(T0 & (1ULL << 63)))
-                break;
-            T0 <<= 1;
-        }
-        T0 = n;
-    }
+    T0 = clo64(T0);
     RETURN();
 }
 
 void op_dclz (void)
 {
-    int n;
-
-    if (T0 == 0) {
-        T0 = 64;
-    } else {
-        for (n = 0; n < 64; n++) {
-            if (T0 & (1ULL << 63))
-                break;
-            T0 <<= 1;
-        }
-        T0 = n;
-    }
+    T0 = clz64(T0);
     RETURN();
 }
+#endif /* TARGET_LONG_BITS > HOST_LONG_BITS */
 #endif /* TARGET_MIPSN32 || TARGET_MIPS64 */
 
 /* 64 bits arithmetic */
Index: qemu-work/target-mips/op_helper.c
===================================================================
--- qemu-work.orig/target-mips/op_helper.c	2007-10-26 22:42:15.000000000 +0100
+++ qemu-work/target-mips/op_helper.c	2007-10-27 12:13:30.000000000 +0100
@@ -20,6 +20,8 @@
 #include <stdlib.h>
 #include "exec.h"
 
+#include "host-utils.h"
+
 #define GETPC() (__builtin_return_address(0))
 
 /*****************************************************************************/
@@ -141,6 +143,17 @@
     } else
        T0 = T1;
 }
+
+void do_dclo (void)
+{
+    T0 = clo64(T0);
+}
+
+void do_dclz (void)
+{
+    T0 = clz64(T0);
+}
+
 #endif /* TARGET_LONG_BITS > HOST_LONG_BITS */
 #endif /* TARGET_MIPSN32 || TARGET_MIPS64 */