Add trace flag for propagate_constant (#1686)

This will show whats being replaced with a constant. This is useful for debugging where a literal comes from.

src/propagate_constant.cpp

@@ -27,11 +27,14 @@
 #include <migraphx/literal.hpp>
 #include <migraphx/functional.hpp>
 #include <migraphx/par_for.hpp>
+#include <migraphx/env.hpp>
 #include <unordered_set>
 
 namespace migraphx {
 inline namespace MIGRAPHX_INLINE_NS {
 
+MIGRAPHX_DECLARE_ENV_VAR(MIGRAPHX_TRACE_PROPAGATE_CONSTANT)
+
 bool skip_propogate(instruction_ref ins)
 {
     if(ins->name() == "contiguous")
@@ -85,6 +88,19 @@ void propagate_constant::apply(module& m) const
     {
         if(not literals[i].empty())
         {
+            if(enabled(MIGRAPHX_TRACE_PROPAGATE_CONSTANT{}))
+            {
+                std::cout << "Constant replace: " << std::endl;
+                std::vector<instruction_ref> inss;
+                fix([&](auto self, auto ins) {
+                    if(contains(inss, ins))
+                        return;
+                    for(auto input : ins->inputs())
+                        self(input);
+                    inss.push_back(ins);
+                })(const_instrs_vec[i]);
+                m.debug_print(inss);
+            }
             assert(literals[i].get_shape() == const_instrs_vec[i]->get_shape());
             auto l = m.add_literal(literals[i].get_shape(), literals[i].data());
             m.replace_instruction(const_instrs_vec[i], l);