Introduce ternop_cond_operation

This adds class ternop_cond_operation, which implements TERNOP_COND.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class ternop_cond_operation): New.
	* ax-gdb.c (ternop_cond_operation::do_generate_ax): New method.

3 files changed, 65 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c3fc9c8..5eb9dca 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
+	* expop.h (class ternop_cond_operation): New.
+	* ax-gdb.c (ternop_cond_operation::do_generate_ax): New method.
+
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
 	* expop.h (class ternop_slice_operation): New.
 	* eval.c (eval_op_ternop): No longer static.
 
diff --git a/gdb/ax-gdb.c b/gdb/ax-gdb.c
index e25e294..87aa210 100644
--- a/gdb/ax-gdb.c
+++ b/gdb/ax-gdb.c
@@ -2390,6 +2390,35 @@ internalvar_operation::do_generate_ax (struct expression *exp,
 	     "expressions cannot use convenience variables."), name);
 }
 
+void
+ternop_cond_operation::do_generate_ax (struct expression *exp,
+				       struct agent_expr *ax,
+				       struct axs_value *value,
+				       struct type *cast_type)
+{
+  struct axs_value value1, value2, value3;
+  int if1, end;
+
+  std::get<0> (m_storage)->generate_ax (exp, ax, &value1);
+  gen_usual_unary (ax, &value1);
+  /* For (A ? B : C), it's easiest to generate subexpression
+     bytecodes in order, but if_goto jumps on true, so we invert
+     the sense of A.  Then we can do B by dropping through, and
+     jump to do C.  */
+  gen_logical_not (ax, &value1, builtin_type (ax->gdbarch)->builtin_int);
+  if1 = ax_goto (ax, aop_if_goto);
+  std::get<1> (m_storage)->generate_ax (exp, ax, &value2);
+  gen_usual_unary (ax, &value2);
+  end = ax_goto (ax, aop_goto);
+  ax_label (ax, if1, ax->len);
+  std::get<2> (m_storage)->generate_ax (exp, ax, &value3);
+  gen_usual_unary (ax, &value3);
+  ax_label (ax, end, ax->len);
+  /* This is arbitrary - what if B and C are incompatible types? */
+  value->type = value2.type;
+  value->kind = value2.kind;
+}
+
 }
 
 /* This handles the middle-to-right-side of code generation for binary
diff --git a/gdb/expop.h b/gdb/expop.h
index 436a011..0f5b504 100644
--- a/gdb/expop.h
+++ b/gdb/expop.h
@@ -734,6 +734,37 @@ public:
   { return TERNOP_SLICE; }
 };
 
+class ternop_cond_operation
+  : public maybe_constant_operation<operation_up, 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
+  {
+    struct value *val
+      = std::get<0> (m_storage)->evaluate (nullptr, exp, noside);
+
+    if (value_logical_not (val))
+      return std::get<2> (m_storage)->evaluate (nullptr, exp, noside);
+    return std::get<1> (m_storage)->evaluate (nullptr, exp, noside);
+  }
+
+  enum exp_opcode opcode () const override
+  { return TERNOP_COND; }
+
+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 */