target-sh4: improve TLB

SH4 is using 16-bit instructions which means most of the constants are
loaded through a constant pool at the end of the subroutine. The same
memory page is therefore accessed in exec and read mode.

With the current implementation, a QEMU TLB entry is set to read or
read/write mode after an UTLB search and to exec mode after an ITLB
search, which causes a lot of TLB exceptions to switch from read or
read/write to exec and vice versa.

This patch optimizes that by already setting the QEMU TLB entry in read
or read/write mode when an UTLB entry is copied into ITLB (during an
ITLB miss). This improve the emulation speed by about 14%.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

target-sh4/helper.c

@@ -280,35 +280,40 @@ static void increment_urc(CPUState * env)
     env->mmucr = (env->mmucr & 0xffff03ff) | (urc << 10);
 }
 
-/* Find itlb entry - update itlb from utlb if necessary and asked for
+/* Copy and utlb entry into itlb
+   Return entry
+*/
+static int copy_utlb_entry_itlb(CPUState *env, int utlb)
+{
+    int itlb;
+
+    tlb_t * ientry;
+    itlb = itlb_replacement(env);
+    ientry = &env->itlb[itlb];
+    if (ientry->v) {
+        tlb_flush_page(env, ientry->vpn << 10);
+    }
+    *ientry = env->utlb[utlb];
+    update_itlb_use(env, itlb);
+    return itlb;
+}
+
+/* Find itlb entry
    Return entry, MMU_ITLB_MISS, MMU_ITLB_MULTIPLE or MMU_DTLB_MULTIPLE
-   Update the itlb from utlb if update is not 0
 */
 static int find_itlb_entry(CPUState * env, target_ulong address,
-                           int use_asid, int update)
+                           int use_asid)
 {
-    int e, n;
+    int e;
 
     e = find_tlb_entry(env, address, env->itlb, ITLB_SIZE, use_asid);
-    if (e == MMU_DTLB_MULTIPLE)
+    if (e == MMU_DTLB_MULTIPLE) {
 	e = MMU_ITLB_MULTIPLE;
-    else if (e == MMU_DTLB_MISS && update) {
-	e = find_tlb_entry(env, address, env->utlb, UTLB_SIZE, use_asid);
-	if (e >= 0) {
-	    tlb_t * ientry;
-	    n = itlb_replacement(env);
-	    ientry = &env->itlb[n];
-	    if (ientry->v) {
-                tlb_flush_page(env, ientry->vpn << 10);
-	    }
-	    *ientry = env->utlb[e];
-	    e = n;
-	} else if (e == MMU_DTLB_MISS)
-	    e = MMU_ITLB_MISS;
-    } else if (e == MMU_DTLB_MISS)
+    } else if (e == MMU_DTLB_MISS) {
 	e = MMU_ITLB_MISS;
-    if (e >= 0)
+    } else if (e >= 0) {
 	update_itlb_use(env, e);
+    }
     return e;
 }
 
@@ -340,13 +345,31 @@ static int get_mmu_address(CPUState * env, target_ulong * physical,
     use_asid = (env->mmucr & MMUCR_SV) == 0 || (env->sr & SR_MD) == 0;
 
     if (rw == 2) {
-	n = find_itlb_entry(env, address, use_asid, 1);
+        n = find_itlb_entry(env, address, use_asid);
 	if (n >= 0) {
 	    matching = &env->itlb[n];
 	    if (!(env->sr & SR_MD) && !(matching->pr & 2))
 		n = MMU_ITLB_VIOLATION;
 	    else
 		*prot = PAGE_EXEC;
+        } else {
+            n = find_utlb_entry(env, address, use_asid);
+            if (n >= 0) {
+                n = copy_utlb_entry_itlb(env, n);
+                matching = &env->itlb[n];
+                if (!(env->sr & SR_MD) && !(matching->pr & 2)) {
+                      n = MMU_ITLB_VIOLATION;
+                } else {
+                    *prot = PAGE_READ | PAGE_EXEC;
+                    if ((matching->pr & 1) && matching->d) {
+                        *prot |= PAGE_WRITE;
+                    }
+                }
+            } else if (n == MMU_DTLB_MULTIPLE) {
+                n = MMU_ITLB_MULTIPLE;
+            } else if (n == MMU_DTLB_MISS) {
+                n = MMU_ITLB_MISS;
+            }
 	}
     } else {
 	n = find_utlb_entry(env, address, use_asid);