m68k: fix CAS2 writeback when Dc1==Dc2

According to Programmer's Reference Manual, if Dc1 and Dc2 specify the
same data register and the comparison fails, memory operand 1 is stored
in the data register.

The current helpers wrote Dc1 then Dc2, leaving operand 2 in the shared
register.

Swap the writeback order for cas2w/cas2l so memory operand 1 wins.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20251226213707.331741-1-laurent@vivier.eu>

diff --git a/target/m68k/op_helper.c b/target/m68k/op_helper.c
index e9c20a8e0322fe80edc6e1fb119302ad18bd898f..10266b1e0e8bb67f6812999916bcf23f5838da38 100644 (file)
--- a/target/m68k/op_helper.c
+++ b/target/m68k/op_helper.c
@@ -799,8 +799,8 @@ void HELPER(cas2w)(CPUM68KState *env, uint32_t regs, uint32_t a1, uint32_t a2)
         env->cc_v = c2;
     }
     env->cc_op = CC_OP_CMPW;
-    env->dregs[Dc1] = deposit32(env->dregs[Dc1], 0, 16, l1);
     env->dregs[Dc2] = deposit32(env->dregs[Dc2], 0, 16, l2);
+    env->dregs[Dc1] = deposit32(env->dregs[Dc1], 0, 16, l1);
 }
 
 static void do_cas2l(CPUM68KState *env, uint32_t regs, uint32_t a1, uint32_t a2,
@@ -861,8 +861,8 @@ static void do_cas2l(CPUM68KState *env, uint32_t regs, uint32_t a1, uint32_t a2,
         env->cc_v = c2;
     }
     env->cc_op = CC_OP_CMPL;
-    env->dregs[Dc1] = l1;
     env->dregs[Dc2] = l2;
+    env->dregs[Dc1] = l1;
 }
 
 void HELPER(cas2l)(CPUM68KState *env, uint32_t regs, uint32_t a1, uint32_t a2)