Re: [PATCH v5 17/36] tcg: Split out tcg_gen_nonatomic_cmpxchg_i{32,64}

[Richard Henderson]

On 1/26/23 14:53, Philippe Mathieu-Daudé wrote:

On 26/1/23 05:38, Richard Henderson wrote:

Normally this is automatically handled by the CF_PARALLEL checks
with in tcg_gen_atomic_cmpxchg_i{32,64}, but x86 has a special
case of !PREFIX_LOCK where it always wants the non-atomic version.

Split these out so that x86 does not have to roll its own.

Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
---
  include/tcg/tcg-op.h |   4 ++
  tcg/tcg-op.c         | 154 +++++++++++++++++++++++++++----------------
  2 files changed, 101 insertions(+), 57 deletions(-)

+void tcg_gen_nonatomic_cmpxchg_i64(TCGv_i64 retv, TCGv addr, TCGv_i64 cmpv,
+                                   TCGv_i64 newv, TCGArg idx, MemOp memop)
+{
+    TCGv_i64 t1, t2;
+

This block from here ...

+    if (TCG_TARGET_REG_BITS == 32 && (memop & MO_SIZE) < MO_64) {
+        tcg_gen_nonatomic_cmpxchg_i32(TCGV_LOW(retv), addr, TCGV_LOW(cmpv),
+                                      TCGV_LOW(newv), idx, memop);
+        if (memop & MO_SIGN) {
+            tcg_gen_sari_i32(TCGV_HIGH(retv), TCGV_LOW(retv), 31);
+        } else {
+            tcg_gen_movi_i32(TCGV_HIGH(retv), 0);
+        }
+        return;
+    }

... to here,

+    t1 = tcg_temp_new_i64();
+    t2 = tcg_temp_new_i64();
+
+    tcg_gen_ext_i64(t2, cmpv, memop & MO_SIZE);
+
+    tcg_gen_qemu_ld_i64(t1, addr, idx, memop & ~MO_SIGN);
+    tcg_gen_movcond_i64(TCG_COND_EQ, t2, t1, t2, newv, t1);
+    tcg_gen_qemu_st_i64(t2, addr, idx, memop);
+    tcg_temp_free_i64(t2);
+
+    if (memop & MO_SIGN) {
+        tcg_gen_ext_i64(retv, t1, memop);
+    } else {
+        tcg_gen_mov_i64(retv, t1);
+    }
+    tcg_temp_free_i64(t1);
  }
  void tcg_gen_atomic_cmpxchg_i64(TCGv_i64 retv, TCGv addr, TCGv_i64 cmpv,
                                  TCGv_i64 newv, TCGArg idx, MemOp memop)
  {
-    memop = tcg_canonicalize_memop(memop, 1, 0);
-
      if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
-        TCGv_i64 t1 = tcg_temp_new_i64();
-        TCGv_i64 t2 = tcg_temp_new_i64();
+        tcg_gen_nonatomic_cmpxchg_i64(retv, addr, cmpv, newv, idx, memop);
+        return;
+    }
-        tcg_gen_ext_i64(t2, cmpv, memop & MO_SIZE);
-
-        tcg_gen_qemu_ld_i64(t1, addr, idx, memop & ~MO_SIGN);
-        tcg_gen_movcond_i64(TCG_COND_EQ, t2, t1, t2, newv, t1);
-        tcg_gen_qemu_st_i64(t2, addr, idx, memop);
-        tcg_temp_free_i64(t2);
-
-        if (memop & MO_SIGN) {
-            tcg_gen_ext_i64(retv, t1, memop);
-        } else {
-            tcg_gen_mov_i64(retv, t1);
-        }
-        tcg_temp_free_i64(t1);
-    } else if ((memop & MO_SIZE) == MO_64) {
-#ifdef CONFIG_ATOMIC64
+    if ((memop & MO_SIZE) == MO_64) {
          gen_atomic_cx_i64 gen;
-        MemOpIdx oi;
+        memop = tcg_canonicalize_memop(memop, 1, 0);
          gen = table_cmpxchg[memop & (MO_SIZE | MO_BSWAP)];
-        tcg_debug_assert(gen != NULL);
+        if (gen) {
+            MemOpIdx oi = make_memop_idx(memop, idx);
+            gen(retv, cpu_env, addr, cmpv, newv, tcg_constant_i32(oi));
+            return;
+        }
-        oi = make_memop_idx(memop, idx);
-        gen(retv, cpu_env, addr, cmpv, newv, tcg_constant_i32(oi));
-#else
          gen_helper_exit_atomic(cpu_env);
-        /* Produce a result, so that we have a well-formed opcode stream
-           with respect to uses of the result in the (dead) code following.  */
+
+        /*
+         * Produce a result for a well-formed opcode stream.  This satisfies
+         * liveness for set before used, which happens before this dead code
+         * is removed.
+         */
          tcg_gen_movi_i64(retv, 0);
-#endif /* CONFIG_ATOMIC64 */
+        return;
+    }

and this one here:

+    if (TCG_TARGET_REG_BITS == 32) {
+        tcg_gen_atomic_cmpxchg_i32(TCGV_LOW(retv), addr, TCGV_LOW(cmpv),
+                                   TCGV_LOW(newv), idx, memop);
+        if (memop & MO_SIGN) {
+            tcg_gen_sari_i32(TCGV_HIGH(retv), TCGV_LOW(retv), 31);
+        } else {
+            tcg_gen_movi_i32(TCGV_HIGH(retv), 0);
+        }

belong to a subsequent patch IMO.

No.  That code is in there now, and needs to be there for correctness.

It gets duplicated in the exposure of the non-atomic code path.


r~


 Otherwise LGTM.

      } else {
          TCGv_i32 c32 = tcg_temp_new_i32();
          TCGv_i32 n32 = tcg_temp_new_i32();