Add delay to FFI annotation.

This allows users to specify the delay of an FFI call in the IR. If the user does not provide a delay, they can use the --ffi_fallback_delay_ps flag. However, this user-provided value overrides the value from the --ffi_fallback_delay_ps flag.

PiperOrigin-RevId: 687418386

xls/estimators/delay_model/ffi_delay_estimator.cc

@@ -19,6 +19,7 @@
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
 #include "absl/strings/str_format.h"
+#include "xls/ir/function_base.h"
 #include "xls/ir/op.h"
 
 namespace xls {
@@ -29,6 +30,12 @@ absl::StatusOr<int64_t> FfiDelayEstimator::GetOperationDelayInPs(
         absl::StrFormat("FFI delay estimate only for kInvoke, found %s",
                         OpToString(node->op())));
   }
+  // If the user does not want to provide one, they can use the value from
+  // the --ffi_fallback_delay_ps flag. However, this user-provided value
+  // overrides the value from the --ffi_fallback_delay_ps flag.
+  if (node->function_base()->ForeignFunctionData()->has_delay_ps()) {
+    return node->function_base()->ForeignFunctionData()->delay_ps();
+  }
   if (!fallback_delay_estimate_.has_value()) {
     return absl::NotFoundError("No --ffi_fallback_delay_ps provided.");
   }

xls/ir/foreign_function.cc

@@ -77,6 +77,9 @@ FfiPartialValueSubstituteHelper::GetUpdatedFfiData() const {
       CodeTemplate::Escaped::kKeep);
   ForeignFunctionData result;
   result.set_code_template(modified_template);
+  if (ffi_->has_delay_ps()) {
+    result.set_delay_ps(ffi_->delay_ps());
+  }
   return result;
 }
 

xls/ir/foreign_function_data.proto

@@ -21,5 +21,6 @@ package xls;
 // the external function instantiation.
 message ForeignFunctionData {
   string code_template = 1;
-  // TODO(hzeller): 2023-07-05 Add optional delay model information.
+  optional int32 delay_ps = 2;
+  // TODO(hzeller): 2023-07-05 Add optional delay model information?
 }

xls/ir/foreign_function_test.cc

@@ -24,12 +24,16 @@ namespace {
 TEST(ForeignFunctionTest, PartialValueSubstituteHelper) {
   ForeignFunctionData ffi;
   ffi.set_code_template("Some {foo} at {bar} with {baz}");
+  // Setting some non-zero delay to make sure it is preserved.
+  ffi.set_delay_ps(1536);
   FfiPartialValueSubstituteHelper substitute(ffi);
   substitute.SetNamedValue("foo", Value(UBits(0xf00d, 16)));
   // '{bar}', we want to keep as-is.
   substitute.SetNamedValue("baz", Value(UBits(0xc0ffee, 24)));
   EXPECT_EQ(substitute.GetUpdatedFfiData()->code_template(),
             "Some 16'hf00d at {bar} with 24'hc0ffee");
+  EXPECT_EQ(ffi.delay_ps(), 1536);
+  EXPECT_EQ(substitute.GetUpdatedFfiData()->delay_ps(), 1536);
 }
 }  // namespace
 }  // namespace xls