From 0026a73ca0a4f7329ef7ffaf41e15ca935a7120f Mon Sep 17 00:00:00 2001
From: Geza Lore <glore@tenstorrent.com>
Date: Wed, 3 Jun 2026 08:41:33 +0100
Subject: [PATCH] Optimize DPI import argument passing (#7704)

Pass inputs to DPI import wrappers by reference (unless fits in a
register). This eliminates a lot of temporary constructors/destructors.
---
 src/V3Task.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/V3Task.cpp b/src/V3Task.cpp
index bb0c00032..0238f89cb 100644
--- a/src/V3Task.cpp
+++ b/src/V3Task.cpp
@@ -1405,6 +1405,13 @@ class TaskVisitor final : public VNVisitor {
                         unlinkAndClone(nodep, portp, false);
                         portp->funcLocal(true);
                         cfuncp->addArgsp(portp);
+                        // Pass inputs to DPI import wrappers by reference, unless fits in register
+                        if (cfuncp->dpiImportWrapper() && portp->isReadOnly()) {
+                            AstNodeDType* const dtypep = portp->dtypep()->skipRefp();
+                            if (dtypep->isCompound() || dtypep->isWide()) {
+                                portp->direction(VDirection::CONSTREF);
+                            }
+                        }
                     } else {
                         // "Normal" variable, mark inside function
                         portp->funcLocal(true);