[PATCH 103/203] Introduce comma_operation

Tom Tromey
2021-01-01T21:48:39Z

This adds class comma_operation, which implements BINOP_COMMA.

gdb/ChangeLog
2021-01-01 Tom Tromey <tom@tromey.com>

* ax-gdb.c (comma_operation::do_generate_ax): New method.
---
gdb/ChangeLog | 4 ++++
gdb/ax-gdb.c | 22 ++++++++++++++++++++++
gdb/expop.h | 31 +++++++++++++++++++++++++++++++
3 files changed, 57 insertions(+)

diff --git a/gdb/ax-gdb.c b/gdb/ax-gdb.c
index 332840456fe..8d5e4fff903 100644
--- a/gdb/ax-gdb.c
+++ b/gdb/ax-gdb.c
@@ -2469,6 +2469,28 @@ repeat_operation::do_generate_ax (struct expression *exp,
value->type = array;
}

+void
+comma_operation::do_generate_ax (struct expression *exp,
+ struct agent_expr *ax,
+ struct axs_value *value,
+ struct type *cast_type)
+{
+ /* Note that we need to be a little subtle about generating code
+ for comma. In C, we can do some optimizations here because
+ we know the left operand is only being evaluated for effect.
+ However, if the tracing kludge is in effect, then we always
+ need to evaluate the left hand side fully, so that all the
+ variables it mentions get traced. */
+ struct axs_value value1;
+ std::get<0> (m_storage)->generate_ax (exp, ax, &value1);
+ /* Don't just dispose of the left operand. We might be tracing,
+ in which case we want to emit code to trace it if it's an
+ lvalue. */
+ gen_traced_pop (ax, &value1);
+ std::get<1> (m_storage)->generate_ax (exp, ax, value);
+ /* It's the consumer's responsibility to trace the right operand. */
+}
+
}

/* This handles the middle-to-right-side of code generation for binary
diff --git a/gdb/expop.h b/gdb/expop.h
index 419ce05abaf..67b265ca8f0 100644
--- a/gdb/expop.h
+++ b/gdb/expop.h
@@ -1197,6 +1197,37 @@ class repeat_operation
override;
};

+/* C-style comma operator. */
+class comma_operation
+ : public maybe_constant_operation<operation_up, operation_up>
+{
+public:
+
+ using maybe_constant_operation::maybe_constant_operation;
+
+ value *evaluate (struct type *expect_type,
+ struct expression *exp,
+ enum noside noside) override
+ {
+ /* The left-hand-side is only evaluated for side effects, so don't
+ bother in other modes. */
+ if (noside == EVAL_NORMAL)
+ std::get<0> (m_storage)->evaluate (nullptr, exp, noside);
+ return std::get<1> (m_storage)->evaluate (nullptr, exp, noside);
+ }
+
+ enum exp_opcode opcode () const override
+ { return BINOP_COMMA; }
+
+protected:
+
+ void do_generate_ax (struct expression *exp,
+ struct agent_expr *ax,
+ struct axs_value *value,
+ struct type *cast_type)
+ override;
+};
+
} /* namespace expr */

#endif /* EXPOP_H */
--
2.26.2