From cb5dd19992fb77ca2be866d9c6f2f4436c8b1c1e Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Thu, 7 Sep 2023 23:01:53 -0700
Subject: Incur l-value conversion cost during overload resolution. (#3195)

* Incur l-value conversion cost during overload resolution.

* Fix compile error.

* cleanup.

---------

Co-authored-by: Yong He <yhe@nvidia.com>
---
 source/slang/slang-check-conversion.cpp | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

(limited to 'source/slang/slang-check-conversion.cpp')

diff --git a/source/slang/slang-check-conversion.cpp b/source/slang/slang-check-conversion.cpp
index 5a9c8df12..c4efba658 100644
--- a/source/slang/slang-check-conversion.cpp
+++ b/source/slang/slang-check-conversion.cpp
@@ -705,7 +705,7 @@ namespace Slang
         CoercionSite site,
         Type*    toType,
         Expr**   outToExpr,
-        Type*    fromType,
+        QualType fromType,
         Expr*    fromExpr,
         ConversionCost* outCost)
     {
@@ -773,7 +773,7 @@ namespace Slang
             auto toBase = toModified ? toModified->getBase() : toType;
             //
             auto fromModified = as<ModifiedType>(fromType);
-            auto fromBase = fromModified ? fromModified->getBase() : fromType;
+            auto fromBase = fromModified ? QualType(fromModified->getBase(), fromType.isLeftValue) : fromType;
 
 
             if((toModified || fromModified) && toBase->equals(fromBase))
@@ -1060,7 +1060,7 @@ namespace Slang
         OverloadResolveContext overloadContext;
         overloadContext.disallowNestedConversions = true;
         overloadContext.argCount = 1;
-        overloadContext.argTypes = &fromType;
+        overloadContext.argTypes = &fromType.type;
         overloadContext.args = &fromExpr;
 
         overloadContext.originalExpr = nullptr;
@@ -1191,6 +1191,11 @@ namespace Slang
                     }
                 }
             }
+            if (fromType.isLeftValue)
+            {
+                // If we are implicitly casting the type of an l-value, we need to impose additional cost.
+                cost += kConversionCost_LValueCast;
+            }
             if(outCost)
                 *outCost = cost;
 
@@ -1245,7 +1250,7 @@ namespace Slang
 
     bool SemanticsVisitor::canCoerce(
         Type*    toType,
-        Type*    fromType,
+        QualType fromType,
         Expr*    fromExpr,
         ConversionCost* outCost)
     {
@@ -1380,7 +1385,7 @@ namespace Slang
 
     bool SemanticsVisitor::canConvertImplicitly(
         Type* toType,
-        Type* fromType)
+        QualType fromType)
     {
         auto conversionCost = getConversionCost(toType, fromType);
 
@@ -1391,7 +1396,7 @@ namespace Slang
         return true;
     }
 
-    ConversionCost SemanticsVisitor::getConversionCost(Type* toType, Type* fromType)
+    ConversionCost SemanticsVisitor::getConversionCost(Type* toType, QualType fromType)
     {
         ConversionCost conversionCost = kConversionCost_Impossible;
         if (!canCoerce(toType, fromType, nullptr, &conversionCost))
-- 
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