tcg: Add TCGContext.emit_before_op

Allow operations to be emitted via normal expanders
into the middle of the opcode stream.

Tested-by: Jørgen Hansen <Jorgen.Hansen@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/tcg/tcg.h

@@ -553,6 +553,12 @@ struct TCGContext {
     QTAILQ_HEAD(, TCGOp) ops, free_ops;
     QSIMPLEQ_HEAD(, TCGLabel) labels;
 
+    /*
+     * When clear, new ops are added to the tail of @ops.
+     * When set, new ops are added in front of @emit_before_op.
+     */
+    TCGOp *emit_before_op;
+
     /* Tells which temporary holds a given register.
        It does not take into account fixed registers */
     TCGTemp *reg_to_temp[TCG_TARGET_NB_REGS];

tcg/tcg.c

@@ -1521,6 +1521,7 @@ void tcg_func_start(TCGContext *s)
 
     QTAILQ_INIT(&s->ops);
     QTAILQ_INIT(&s->free_ops);
+    s->emit_before_op = NULL;
     QSIMPLEQ_INIT(&s->labels);
 
     tcg_debug_assert(s->addr_type == TCG_TYPE_I32 ||
@@ -2332,7 +2333,11 @@ static void tcg_gen_callN(TCGHelperInfo *info, TCGTemp *ret, TCGTemp **args)
     op->args[pi++] = (uintptr_t)info;
     tcg_debug_assert(pi == total_args);
 
-    QTAILQ_INSERT_TAIL(&tcg_ctx->ops, op, link);
+    if (tcg_ctx->emit_before_op) {
+        QTAILQ_INSERT_BEFORE(tcg_ctx->emit_before_op, op, link);
+    } else {
+        QTAILQ_INSERT_TAIL(&tcg_ctx->ops, op, link);
+    }
 
     tcg_debug_assert(n_extend < ARRAY_SIZE(extend_free));
     for (i = 0; i < n_extend; ++i) {
@@ -3215,7 +3220,12 @@ static TCGOp *tcg_op_alloc(TCGOpcode opc, unsigned nargs)
 TCGOp *tcg_emit_op(TCGOpcode opc, unsigned nargs)
 {
     TCGOp *op = tcg_op_alloc(opc, nargs);
-    QTAILQ_INSERT_TAIL(&tcg_ctx->ops, op, link);
+
+    if (tcg_ctx->emit_before_op) {
+        QTAILQ_INSERT_BEFORE(tcg_ctx->emit_before_op, op, link);
+    } else {
+        QTAILQ_INSERT_TAIL(&tcg_ctx->ops, op, link);
+    }
     return op;
 }