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Re: [PATCH v2 1/2] target/s390x: Fix R[NOX]SBG with T=1

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 1/2] target/s390x: Fix R[NOX]SBG with T=1
Date: Thu, 16 Mar 2023 09:41:22 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.8.0

On 16/3/23 00:56, Ilya Leoshkevich wrote:
RXSBG usage in the "filetests" test from the wasmtime testsuite makes
tcg_reg_alloc_op() attempt to temp_load() a TEMP_VAL_DEAD temporary,
causing an assertion failure:

     0x01000a70:  ec14 b040 3057  rxsbg    %r1, %r4, 0xb0, 0x40, 0x30

     OP after optimization and liveness analysis:
      ---- 0000000001000a70 0000000000000004 0000000000000006
      rotl_i64 tmp2,r4,$0x30                   dead: 1 2  pref=0xffff
      and_i64 tmp2,tmp2,$0x800000000000ffff    dead: 1  pref=0xffff
     [xor_i64 tmp3,tmp3,tmp2                   dead: 1 2  pref=0xffff]
      and_i64 cc_dst,tmp3,$0x800000000000ffff  sync: 0  dead: 0 1 2  pref=0xffff
      mov_i64 psw_addr,$0x1000a76              sync: 0  dead: 0 1  pref=0xffff
      mov_i32 cc_op,$0x6                       sync: 0  dead: 0 1  pref=0xffff
      call lookup_tb_ptr,$0x6,$1,tmp8,env      dead: 1  pref=none
      goto_ptr tmp8                            dead: 0
      set_label $L0
      exit_tb $0x7fffe809d183

     ../tcg/tcg.c:3865: tcg fatal error

The reason is that tmp3 does not have an initial value, which confuses
the register allocator. This also affects the correctness of the

Fix by assigning R1 to it.

Fixes: d6c6372e186e ("target-s390: Implement R[NOX]SBG")

Exposed by 3ac6f91bca..dd161de75f?

3ac6f91bca target/s390x: Drop tcg_temp_free from translate.c
dd161de75f target/s390x: Remove g_out, g_out2, g_in1, g_in2

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
  target/s390x/tcg/translate.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
index 14c3896d529..6dd2f41ad08 100644
--- a/target/s390x/tcg/translate.c
+++ b/target/s390x/tcg/translate.c
@@ -3696,10 +3696,13 @@ static DisasJumpType op_rosbg(DisasContext *s, DisasOps 
      int i4 = get_field(s, i4);
      int i5 = get_field(s, i5);
      uint64_t mask;
+    TCGv_i64 tmp;
/* If this is a test-only form, arrange to discard the result. */
      if (i3 & 0x80) {

          tcg_debug_assert(o->out != NULL); ?

+        tmp = o->out;
          o->out = tcg_temp_new_i64();
+        tcg_gen_mov_i64(o->out, tmp);

Something bugs me with this pattern but I can't say why yet :(

i3 &= 63;

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