Re: [PATCH] tcg: Reduce serial context atomicity earlier

[Philippe Mathieu-Daudé]

On 12/12/23 20:35, Richard Henderson wrote:

Reduce atomicity while emitting opcodes, instead of later
during code generation.  This ensures that any helper called
also sees the reduced atomicity requirement.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2034
Signed-off-by: Richard Henderson 
---
  tcg/tcg-op-ldst.c | 28 
  tcg/tcg.c |  9 +
  2 files changed, 25 insertions(+), 12 deletions(-)


Reviewed-by: Philippe Mathieu-Daudé 

Re: [PATCH] tcg: Reduce serial context atomicity earlier

[Alex Bennée]

Richard Henderson  writes:

> Reduce atomicity while emitting opcodes, instead of later
> during code generation.  This ensures that any helper called
> also sees the reduced atomicity requirement.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2034
> Signed-off-by: Richard Henderson 

Tested-by: Alex Bennée 

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro

[PATCH] tcg: Reduce serial context atomicity earlier

[Richard Henderson]

Reduce atomicity while emitting opcodes, instead of later
during code generation.  This ensures that any helper called
also sees the reduced atomicity requirement.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2034
Signed-off-by: Richard Henderson 
---
 tcg/tcg-op-ldst.c | 28 
 tcg/tcg.c |  9 +
 2 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/tcg/tcg-op-ldst.c b/tcg/tcg-op-ldst.c
index e2c55df217..f11043b449 100644
--- a/tcg/tcg-op-ldst.c
+++ b/tcg/tcg-op-ldst.c
@@ -77,6 +77,13 @@ static MemOp tcg_canonicalize_memop(MemOp op, bool is64, 
bool st)
 if (st) {
 op &= ~MO_SIGN;
 }
+
+/* In serial mode, reduce atomicity. */
+if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
+op &= ~MO_ATOM_MASK;
+op |= MO_ATOM_NONE;
+}
+
 return op;
 }
 
@@ -428,8 +435,7 @@ static bool use_two_i64_for_i128(MemOp mop)
 case MO_ATOM_SUBALIGN:
 case MO_ATOM_WITHIN16:
 case MO_ATOM_WITHIN16_PAIR:
-/* In a serialized context, no atomicity is required. */
-return !(tcg_ctx->gen_tb->cflags & CF_PARALLEL);
+return false;
 default:
 g_assert_not_reached();
 }
@@ -499,13 +505,20 @@ static void maybe_free_addr64(TCGv_i64 a64)
 static void tcg_gen_qemu_ld_i128_int(TCGv_i128 val, TCGTemp *addr,
  TCGArg idx, MemOp memop)
 {
-const MemOpIdx orig_oi = make_memop_idx(memop, idx);
+MemOpIdx orig_oi;
 TCGv_i64 ext_addr = NULL;
 TCGOpcode opc;
 
 check_max_alignment(get_alignment_bits(memop));
 tcg_gen_req_mo(TCG_MO_LD_LD | TCG_MO_ST_LD);
 
+/* In serial mode, reduce atomicity. */
+if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
+memop &= ~MO_ATOM_MASK;
+memop |= MO_ATOM_NONE;
+}
+orig_oi = make_memop_idx(memop, idx);
+
 /* TODO: For now, force 32-bit hosts to use the helper. */
 if (TCG_TARGET_HAS_qemu_ldst_i128 && TCG_TARGET_REG_BITS == 64) {
 TCGv_i64 lo, hi;
@@ -608,13 +621,20 @@ void tcg_gen_qemu_ld_i128_chk(TCGv_i128 val, TCGTemp 
*addr, TCGArg idx,
 static void tcg_gen_qemu_st_i128_int(TCGv_i128 val, TCGTemp *addr,
  TCGArg idx, MemOp memop)
 {
-const MemOpIdx orig_oi = make_memop_idx(memop, idx);
+MemOpIdx orig_oi;
 TCGv_i64 ext_addr = NULL;
 TCGOpcode opc;
 
 check_max_alignment(get_alignment_bits(memop));
 tcg_gen_req_mo(TCG_MO_ST_LD | TCG_MO_ST_ST);
 
+/* In serial mode, reduce atomicity. */
+if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
+memop &= ~MO_ATOM_MASK;
+memop |= MO_ATOM_NONE;
+}
+orig_oi = make_memop_idx(memop, idx);
+
 /* TODO: For now, force 32-bit hosts to use the helper. */
 
 if (TCG_TARGET_HAS_qemu_ldst_i128 && TCG_TARGET_REG_BITS == 64) {
diff --git a/tcg/tcg.c b/tcg/tcg.c
index d2ea22b397..896a36caeb 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -5440,15 +5440,8 @@ static TCGAtomAlign atom_and_align_for_opc(TCGContext 
*s, MemOp opc,
 MemOp align = get_alignment_bits(opc);
 MemOp size = opc & MO_SIZE;
 MemOp half = size ? size - 1 : 0;
+MemOp atom = opc & MO_ATOM_MASK;
 MemOp atmax;
-MemOp atom;
-
-/* When serialized, no further atomicity required.  */
-if (s->gen_tb->cflags & CF_PARALLEL) {
-atom = opc & MO_ATOM_MASK;
-} else {
-atom = MO_ATOM_NONE;
-}
 
 switch (atom) {
 case MO_ATOM_NONE:
-- 
2.34.1