vm: new megamorphic hashcode algorithm improves bootstrap speed

basis/cpu/ppc/bootstrap.factor

@@ -224,8 +224,13 @@ CONSTANT: rs-reg 14
 [
     ! cache = ...
     0 3 LOAD32 rc-absolute-ppc-2/2 rt-immediate jit-rel
-    ! key = class
-    5 4 MR
+    ! key = hashcode(class)
+    5 4 3 SRAWI
+    6 4 8 SRAWI
+    5 5 6 ADD
+    6 4 13 SRAWI
+    5 5 6 ADD
+    5 5 3 SLWI
     ! key &= cache.length - 1
     5 5 mega-cache-size get 1 - bootstrap-cell * ANDI
     ! cache += array-start-offset

basis/cpu/x86/bootstrap.factor

@@ -222,9 +222,16 @@ big-endian off
 [
     ! cache = ...
     temp0 0 MOV rc-absolute-cell rt-immediate jit-rel
-    ! key = class
+    ! key = hashcode(class)
     temp2 temp1 MOV
-    bootstrap-cell 8 = [ temp2 1 SHL ] when
+    temp2 3 SHR
+    temp3 temp1 MOV
+    temp3 8 SHR
+    temp2 temp3 ADD
+    temp3 temp1 MOV
+    temp3 13 SHR
+    temp2 temp3 ADD
+    temp2 bootstrap-cell 4 = 3 4 ? SHL
     ! key &= cache.length - 1
     temp2 mega-cache-size get 1 - bootstrap-cell * AND
     ! cache += array-start-offset

vm/dispatch.cpp

@@ -126,7 +126,7 @@ cell factor_vm::object_class(cell obj)
 cell factor_vm::method_cache_hashcode(cell klass, array *array)
 {
 	cell capacity = (array_capacity(array) >> 1) - 1;
-	return ((klass >> TAG_BITS) & capacity) << 1;
+	return (((klass >> 3) + (klass >> 8) + (klass >> 13)) & capacity) << 1;
 }
 
 void factor_vm::update_method_cache(cell cache, cell klass, cell method)