From 1093218d6f0e114eb9fa52d60ca525bf9dd9f98a Mon Sep 17 00:00:00 2001
From: Sai Praveen Bangaru <31557731+saipraveenb25@users.noreply.github.com>
Date: Thu, 20 Oct 2022 14:22:00 -0400
Subject: Modified the new type system to support generic differentiable types
 … (#2413)
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* Modified the new type system to support generic differentiable types and added support for differentiating overloaded functions.

* Changed a few asserts to release asserts to avoid unreferenced variable errors

* Fixed a naming issue with TypeWitnessBreadcumb::Flavor::Decl

* Added logic to avoid tracking differentiable types if the module does not use auto-diff or define differentiable types.

* Moved the auto-diff passes to after the specialization step, added a more complex generics test

* Added a generics stress test and fixed AST-side logic. IR side needs some more work

* Added differential getter and setter logic, fixed multiple issues with DifferentiableTypeDictionary, added support for loops and conditions

* Changed differential getters to use pointer types, added getter type checking

* Fixed some bugs related to diff type registration and differential getters

* Removed some superfluous code

* Removed some more unused code.

* Fixed an issue with witness substitution

* Minor fix

Co-authored-by: Yong He <yonghe@outlook.com>
---
 source/slang/slang-check-constraint.cpp | 43 ++++++++++++++++++++++++---------
 1 file changed, 32 insertions(+), 11 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 24cedd7d5..f96b5a484 100644
--- a/source/slang/slang-check-constraint.cpp
+++ b/source/slang/slang-check-constraint.cpp
@@ -564,6 +564,19 @@ namespace Slang
             }
         }
 
+        // Two subtype witnesses can be unified if they exist (non-null) and 
+        // prove that some pair of types are subtypes of types that can be unified.
+        // 
+        if (auto fstWit = as<SubtypeWitness>(fst))
+        {
+            if (auto sndWit = as<SubtypeWitness>(snd))
+            {
+                return TryUnifyTypes(constraints,
+                    fstWit->sup,
+                    sndWit->sup);
+            }
+        }
+
         SLANG_UNIMPLEMENTED_X("value unification case");
 
         // default: fail
@@ -725,17 +738,29 @@ namespace Slang
 
     bool SemanticsVisitor::TryUnifyConjunctionType(
         ConstraintSystem&   constraints,
-        AndType*            fst,
+        Type*               fst,
         Type*               snd)
     {
-        // Unifying a type `T` with `A & B` amounts to unifying
-        // `T` with `A` and also `T` with `B`.
+        // Unifying a type `A & B` with `T` amounts to unifying
+        // `A` with `T` and also `B` with `T` while
+        // unifying a type `T` with `A & B` amounts to either 
+        // unifying `T` with `A` or `T` with `B`
         //
         // If either unification is impossible, then the full
         // case is also impossible.
         //
-        return TryUnifyTypes(constraints, fst->left, snd)
-            && TryUnifyTypes(constraints, fst->right, snd);
+        if (auto fstAndType = as<AndType>(fst))
+        {
+            return TryUnifyTypes(constraints, fstAndType->left, snd)
+                && TryUnifyTypes(constraints, fstAndType->right, snd);
+        }
+        else if (auto sndAndType = as<AndType>(snd))
+        {
+            return TryUnifyTypes(constraints, fst, sndAndType->left)
+                || TryUnifyTypes(constraints, fst, sndAndType->right);
+        }
+        else
+            return false;
     }
 
     bool SemanticsVisitor::TryUnifyTypes(
@@ -762,13 +787,9 @@ namespace Slang
         // a conjunction directly, and will instead find all of the
         // "leaf" types we need to constrain it to.
         //
-        if( auto fstAndType = as<AndType>(fst) )
-        {
-            return TryUnifyConjunctionType(constraints, fstAndType, snd);
-        }
-        if( auto sndAndType = as<AndType>(snd) )
+        if (as<AndType>(fst) || as<AndType>(snd))
         {
-            return TryUnifyConjunctionType(constraints, sndAndType, fst);
+            return TryUnifyConjunctionType(constraints, fst, snd);
         }
 
         // A generic parameter type can unify with anything.
-- 
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