[GUFA] Fix haveIntersection on comparing nullable with non-nullable (#5089)

We compared types and not heap types, so a difference in nullability
confused us. But at that point in the code, we've ruled out nulls, so we
should focus on heap types only.

3 files changed, 41 insertions, 2 deletions

diff --git a/src/ir/possible-contents.cpp b/src/ir/possible-contents.cpp
index 167890d63..836f7570d 100644
--- a/src/ir/possible-contents.cpp
+++ b/src/ir/possible-contents.cpp
@@ -148,6 +148,14 @@ bool PossibleContents::haveIntersection(const PossibleContents& a,
   auto aType = a.getType();
   auto bType = b.getType();
 
+  if (!aType.isRef() || !bType.isRef()) {
+    // At least one is not a reference. The only way they can intersect is if
+    // the type is identical.
+    return aType == bType;
+  }
+
+  // From here on we focus on references.
+
   if (aType.isNullable() && bType.isNullable()) {
     // Null is possible on both sides. Assume that an intersection can exist,
     // but we could be more precise here and check if the types belong to
@@ -156,12 +164,25 @@ bool PossibleContents::haveIntersection(const PossibleContents& a,
     return true;
   }
 
-  if (a.hasExactType() && b.hasExactType() && a.getType() != b.getType()) {
+  // We ruled out a null on both sides, so at least one is non-nullable. If the
+  // other is a null then no chance for an intersection remains.
+  if (a.isNull() || b.isNull()) {
+    return false;
+  }
+
+  // From here on we focus on references and can ignore the case of null - any
+  // intersection must be of a non-null value, so we can focus on the heap
+  // types.
+  auto aHeapType = aType.getHeapType();
+  auto bHeapType = bType.getHeapType();
+
+  if (a.hasExactType() && b.hasExactType() && aHeapType != bHeapType) {
     // The values must be different since their types are different.
     return false;
   }
 
-  if (!Type::isSubType(aType, bType) && !Type::isSubType(bType, aType)) {
+  if (!HeapType::isSubType(aHeapType, bHeapType) &&
+      !HeapType::isSubType(bHeapType, aHeapType)) {
     // No type can appear in both a and b, so the types differ, so the values
     // differ.
     return false;
diff --git a/test/gtest/possible-contents.cpp b/test/gtest/possible-contents.cpp
index 1e1f0e5c9..933e220bb 100644
--- a/test/gtest/possible-contents.cpp
+++ b/test/gtest/possible-contents.cpp
@@ -280,9 +280,16 @@ TEST_F(PossibleContentsTest, TestIntersection) {
   assertHaveIntersection(exactFuncSignatureType, exactFuncSignatureType);
   assertHaveIntersection(i32Zero, i32One); // TODO: this could be inferred false
 
+  // Exact types only differing by nullability can intersect (not on the null,
+  // but on something else).
+  assertHaveIntersection(exactAnyref, exactNonNullAnyref);
+
   // Due to subtyping, an intersection might exist.
   assertHaveIntersection(funcGlobal, funcGlobal);
   assertHaveIntersection(funcGlobal, exactFuncSignatureType);
+  assertHaveIntersection(nonNullFuncGlobal, exactFuncSignatureType);
+  assertHaveIntersection(funcGlobal, exactNonNullFuncSignatureType);
+  assertHaveIntersection(nonNullFuncGlobal, exactNonNullFuncSignatureType);
 
   // Neither is a subtype of the other, but nulls are possible, so a null can be
   // the intersection.
diff --git a/test/lit/passes/gufa-refs.wast b/test/lit/passes/gufa-refs.wast
index 24ebda381..42f1b349d 100644
--- a/test/lit/passes/gufa-refs.wast
+++ b/test/lit/passes/gufa-refs.wast
@@ -2766,6 +2766,9 @@
   ;; CHECK-NEXT:  (drop
   ;; CHECK-NEXT:   (i32.const 0)
   ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (i32.const 0)
+  ;; CHECK-NEXT:  )
   ;; CHECK-NEXT: )
   (func $ref.eq-zero (export "ref.eq-zero")
     ;; We do not track specific references, so only the types can be used here.
@@ -2791,6 +2794,14 @@
         )
       )
     )
+    (drop
+      (ref.eq
+        (struct.new $struct
+          (i32.const 5)
+        )
+        (ref.null $struct)
+      )
+    )
   )
 
   ;; CHECK:      (func $ref.eq-unknown (type $i32_ref?|$struct|_ref?|$struct|_ref?|$other|_ref|$struct|_ref|$struct|_ref|$other|_=>_none) (param $x i32) (param $struct (ref null $struct)) (param $struct2 (ref null $struct)) (param $other (ref null $other)) (param $nn-struct (ref $struct)) (param $nn-struct2 (ref $struct)) (param $nn-other (ref $other))