compiler: fix ranging over maps with particular map types

Some map keys are hard to compare, such as floats. They are stored as if
the map keys are of interface type instead of the key type itself. This
makes working with them in the runtime package easier: they are compared
as regular interfaces.

Iterating over maps didn't care about this special case though. It just
returns the key, value pair as it is stored in the map. This is buggy,
and this commit fixes this bug.

compiler/map.go

@@ -171,19 +171,59 @@ func (b *builder) createMapDelete(keyType types.Type, m, key llvm.Value, pos tok
 // map. It returns a tuple of {bool, key, value} with the result of the
 // iteration.
 func (b *builder) createMapIteratorNext(rangeVal ssa.Value, llvmRangeVal, it llvm.Value) llvm.Value {
-	llvmKeyType := b.getLLVMType(rangeVal.Type().Underlying().(*types.Map).Key())
-	llvmValueType := b.getLLVMType(rangeVal.Type().Underlying().(*types.Map).Elem())
+	// Determine the type of the values to return from the *ssa.Next
+	// instruction. It is returned as {bool, keyType, valueType}.
+	keyType := rangeVal.Type().Underlying().(*types.Map).Key()
+	valueType := rangeVal.Type().Underlying().(*types.Map).Elem()
+	llvmKeyType := b.getLLVMType(keyType)
+	llvmValueType := b.getLLVMType(valueType)
 
-	mapKeyAlloca, mapKeyPtr, mapKeySize := b.createTemporaryAlloca(llvmKeyType, "range.key")
+	// There is a special case in which keys are stored as an interface value
+	// instead of the value they normally are. This happens for non-trivially
+	// comparable types such as float32 or some structs.
+	isKeyStoredAsInterface := false
+	if t, ok := keyType.Underlying().(*types.Basic); ok && t.Info()&types.IsString != 0 {
+		// key is a string
+	} else if hashmapIsBinaryKey(keyType) {
+		// key can be compared with runtime.memequal
+	} else {
+		// The key is stored as an interface value, and may or may not be an
+		// interface type (for example, float32 keys are stored as an interface
+		// value).
+		if _, ok := keyType.Underlying().(*types.Interface); !ok {
+			isKeyStoredAsInterface = true
+		}
+	}
+
+	// Determine the type of the key as stored in the map.
+	llvmStoredKeyType := llvmKeyType
+	if isKeyStoredAsInterface {
+		llvmStoredKeyType = b.getLLVMRuntimeType("_interface")
+	}
+
+	// Extract the key and value from the map.
+	mapKeyAlloca, mapKeyPtr, mapKeySize := b.createTemporaryAlloca(llvmStoredKeyType, "range.key")
 	mapValueAlloca, mapValuePtr, mapValueSize := b.createTemporaryAlloca(llvmValueType, "range.value")
 	ok := b.createRuntimeCall("hashmapNext", []llvm.Value{llvmRangeVal, it, mapKeyPtr, mapValuePtr}, "range.next")
+	mapKey := b.CreateLoad(mapKeyAlloca, "")
+	mapValue := b.CreateLoad(mapValueAlloca, "")
 
-	tuple := llvm.Undef(b.ctx.StructType([]llvm.Type{b.ctx.Int1Type(), llvmKeyType, llvmValueType}, false))
-	tuple = b.CreateInsertValue(tuple, ok, 0, "")
-	tuple = b.CreateInsertValue(tuple, b.CreateLoad(mapKeyAlloca, ""), 1, "")
-	tuple = b.CreateInsertValue(tuple, b.CreateLoad(mapValueAlloca, ""), 2, "")
+	if isKeyStoredAsInterface {
+		// The key is stored as an interface but it isn't of interface type.
+		// Extract the underlying value.
+		mapKey = b.extractValueFromInterface(mapKey, llvmKeyType)
+	}
+
+	// End the lifetimes of the allocas, because we're done with them.
 	b.emitLifetimeEnd(mapKeyPtr, mapKeySize)
 	b.emitLifetimeEnd(mapValuePtr, mapValueSize)
+
+	// Construct the *ssa.Next return value: {ok, mapKey, mapValue}
+	tuple := llvm.Undef(b.ctx.StructType([]llvm.Type{b.ctx.Int1Type(), llvmKeyType, llvmValueType}, false))
+	tuple = b.CreateInsertValue(tuple, ok, 0, "")
+	tuple = b.CreateInsertValue(tuple, mapKey, 1, "")
+	tuple = b.CreateInsertValue(tuple, mapValue, 2, "")
+
 	return tuple
 }