[jit] Make alias analysis properly handle alias cloberring

Alias analysis attempts to remove indirection when using OP_LDADDR (which fetches the address of a variable). For example :

	ldaddr r1 <- r0
	load_mem r2 <- r1

is equivalent to

	mov r2 <- r0

The remembered r1 alias needs to be forgotten in case r1 is changed. We were handling this for direct assignment with MOV, but not for the more subtle case where an alias to r1 would be passed to a call, which could lead to changing r1.

mono#14872

mono/mini/alias-analysis.c

@@ -150,6 +150,30 @@ lower_store_imm (MonoCompile *cfg, MonoInst *store, MonoInst *ldaddr)
 	return TRUE;
 }
 
+static void
+kill_call_arg_alias (MonoCompile *cfg, GHashTable *addr_loads, GSList *l)
+{
+	for (; l; l = l->next) {
+		MonoInst *tmp;
+		guint32 regpair, reg;
+
+		regpair = (guint32)(gssize)(l->data);
+		reg = regpair & 0xffffff;
+
+		tmp = (MonoInst *)g_hash_table_lookup (addr_loads, GINT_TO_POINTER (reg));
+		if (tmp) {
+			// This call passes an alias as an argument. This means that the contents
+			// of the passed pointer can change. If the content is also an alias then
+			// we need to forget it as we do for moves.
+			if (g_hash_table_remove (addr_loads, GINT_TO_POINTER (((MonoInst*)tmp->inst_p0)->dreg))) {
+				if (cfg->verbose_level > 2)
+					printf ("Killed alias %d\n", ((MonoInst*)tmp->inst_p0)->dreg);
+			}
+
+		}
+	}
+}
+
 static gboolean
 lower_memory_access (MonoCompile *cfg)
 {
@@ -264,6 +288,17 @@ lower_memory_access (MonoCompile *cfg)
 					needs_dce = TRUE;
 				}
 				break;
+			default: {
+				if (MONO_IS_CALL (ins)) {
+					MonoCallInst *call = (MonoCallInst*)ins;
+
+					kill_call_arg_alias (cfg, addr_loads, call->out_ireg_args);
+				}
+				// FIXME Kill more aliases if used as dreg, since we are not in ssa form.
+				// This would need some optimizations so we don't lookup hash table for every
+				// instruction
+				break;
+			}
 			}
 		}
 	}