From 19867ffca6dca7995c799354081219c9e76f13d1 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Thu, 20 Feb 2025 14:48:51 -0800
Subject: Simplify implicit cast ctors for vector & matrix. (#6408)

* Simplify implicit cast ctors for vector & matrix.

* Fix formatting.

* Fix tests.

* Fix Falcor test.

* Mark __builtin_cast as internal.
---
 source/slang/slang-check-constraint.cpp | 59 +++++++++++++++++++++++++++++----
 1 file changed, 52 insertions(+), 7 deletions(-)

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

diff --git a/source/slang/slang-check-constraint.cpp b/source/slang/slang-check-constraint.cpp
index 872d2616c..642a4bf6a 100644
--- a/source/slang/slang-check-constraint.cpp
+++ b/source/slang/slang-check-constraint.cpp
@@ -715,13 +715,6 @@ DeclRef<Decl> SemanticsVisitor::trySolveConstraintSystem(
         // system as being solved now, as a result of the witness we found.
     }
 
-    // Add a flat cost to all unconstrained generic params.
-    for (auto typeParamDecl : genericDeclRef.getDecl()->getMembersOfType<GenericTypeParamDecl>())
-    {
-        if (!constrainedGenericParams.contains(typeParamDecl))
-            outBaseCost += kConversionCost_UnconstraintGenericParam;
-    }
-
     // Make sure we haven't constructed any spurious constraints
     // that we aren't able to satisfy:
     for (auto c : system->constraints)
@@ -732,6 +725,58 @@ DeclRef<Decl> SemanticsVisitor::trySolveConstraintSystem(
         }
     }
 
+    // Verify that all type coercion constraints can be satisfied.
+    for (auto constraintDecl :
+         genericDeclRef.getDecl()->getMembersOfType<TypeCoercionConstraintDecl>())
+    {
+        DeclRef<TypeCoercionConstraintDecl> constraintDeclRef =
+            m_astBuilder
+                ->getGenericAppDeclRef(
+                    genericDeclRef,
+                    args.getArrayView().arrayView,
+                    constraintDecl)
+                .as<TypeCoercionConstraintDecl>();
+        auto fromType = constraintDeclRef.substitute(m_astBuilder, constraintDecl->fromType.Ptr());
+        auto toType = constraintDeclRef.substitute(m_astBuilder, constraintDecl->toType.Ptr());
+        auto conversionCost = getConversionCost(toType, fromType);
+        if (constraintDecl->findModifier<ImplicitConversionModifier>())
+        {
+            if (conversionCost > kConversionCost_GeneralConversion)
+            {
+                // The type arguments are not implicitly convertible, return failure.
+                return DeclRef<Decl>();
+            }
+        }
+        else
+        {
+            if (conversionCost == kConversionCost_Impossible)
+            {
+                // The type arguments are not convertible, return failure.
+                return DeclRef<Decl>();
+            }
+        }
+        if (auto fromDecl = isDeclRefTypeOf<Decl>(constraintDecl->fromType))
+        {
+            constrainedGenericParams.add(fromDecl.getDecl());
+        }
+        if (auto toDecl = isDeclRefTypeOf<Decl>(constraintDecl->toType))
+        {
+            constrainedGenericParams.add(toDecl.getDecl());
+        }
+        // If we are to expand the support of type coercion constraint beyond simple builtin core
+        // module functions, then the witness should be a reference to the conversion function. For
+        // now, this isn't required, and it is not easy to get it from the coercion logic, so we
+        // leave it empty.
+        args.add(m_astBuilder->getTypeCoercionWitness(fromType, toType, DeclRef<Decl>()));
+    }
+
+    // Add a flat cost to all unconstrained generic params.
+    for (auto typeParamDecl : genericDeclRef.getDecl()->getMembersOfType<GenericTypeParamDecl>())
+    {
+        if (!constrainedGenericParams.contains(typeParamDecl))
+            outBaseCost += kConversionCost_UnconstraintGenericParam;
+    }
+
     return m_astBuilder->getGenericAppDeclRef(genericDeclRef, args.getArrayView().arrayView);
 }
 
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