tcg-mips: Move bswap code to a subroutine

Without the mips32r2 instructions to perform swapping, bswap is quite large,
dominating the size of each reverse-endian qemu_ld/qemu_st operation.

Create a subroutine in the prologue block.  The subroutine requires extra
reserved registers (TCG_TMP[2, 3]).  Using these within qemu_ld means that
we need not place additional restrictions on the qemu_ld outputs.

Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Tested-by: James Hogan <james.hogan@imgtec.com>
Tested-by: YunQiang Su <wzssyqa@gmail.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Jin Guojie <jinguojie@loongson.cn>
Message-Id: <1483592275-4496-2-git-send-email-jinguojie@loongson.cn>
diff --git a/tcg/mips/tcg-target.h b/tcg/mips/tcg-target.h
index 3aeac87..a6871fb 100644
--- a/tcg/mips/tcg-target.h
+++ b/tcg/mips/tcg-target.h
@@ -117,11 +117,11 @@
 #define TCG_TARGET_HAS_muls2_i32        (!use_mips32r6_instructions)
 #define TCG_TARGET_HAS_muluh_i32        1
 #define TCG_TARGET_HAS_mulsh_i32        1
+#define TCG_TARGET_HAS_bswap32_i32      1
 
 /* optional instructions detected at runtime */
 #define TCG_TARGET_HAS_movcond_i32      use_movnz_instructions
 #define TCG_TARGET_HAS_bswap16_i32      use_mips32r2_instructions
-#define TCG_TARGET_HAS_bswap32_i32      use_mips32r2_instructions
 #define TCG_TARGET_HAS_deposit_i32      use_mips32r2_instructions
 #define TCG_TARGET_HAS_ext8s_i32        use_mips32r2_instructions
 #define TCG_TARGET_HAS_ext16s_i32       use_mips32r2_instructions