accel/tcg: Introduce is_same_page()

Introduce a function that checks whether a given address is on the same
page as where disassembly started. Having it improves readability of
the following patches.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20220811095534.241224-3-iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
[rth: Make the DisasContextBase parameter const.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/exec/translator.h

@@ -187,4 +187,14 @@ FOR_EACH_TRANSLATOR_LD(GEN_TRANSLATOR_LD)
 
 #undef GEN_TRANSLATOR_LD
 
+/*
+ * Return whether addr is on the same page as where disassembly started.
+ * Translators can use this to enforce the rule that only single-insn
+ * translation blocks are allowed to cross page boundaries.
+ */
+static inline bool is_same_page(const DisasContextBase *db, target_ulong addr)
+{
+    return ((addr ^ db->pc_first) & TARGET_PAGE_MASK) == 0;
+}
+
 #endif /* EXEC__TRANSLATOR_H */