diff --git a/.github/workflows/e2e-tests.yml b/.github/workflows/e2e-tests.yml
index 60d5a23a406..f5989b740b8 100644
--- a/.github/workflows/e2e-tests.yml
+++ b/.github/workflows/e2e-tests.yml
@@ -307,6 +307,11 @@ jobs:
               echo "$OUTPUT"
               ../bashunit -a matches "Note: Using configuration file .+phpstan.neon." "$OUTPUT"
               ../bashunit -a contains 'Result cache not used because the metadata do not match: metaExtensions' "$OUTPUT"
+          - script: |
+              cd e2e/result-cache-restore-without-reflection
+              composer install
+              ../../bin/phpstan -vvv
+              ../../bin/phpstan -vvv
           - script: |
               cd e2e/bug-12606
               export CONFIGTEST=test
diff --git a/e2e/result-cache-restore-without-reflection/.gitignore b/e2e/result-cache-restore-without-reflection/.gitignore
new file mode 100644
index 00000000000..8b7ef350326
--- /dev/null
+++ b/e2e/result-cache-restore-without-reflection/.gitignore
@@ -0,0 +1,2 @@
+/vendor
+composer.lock
diff --git a/e2e/result-cache-restore-without-reflection/composer.json b/e2e/result-cache-restore-without-reflection/composer.json
new file mode 100644
index 00000000000..c0d4ee43781
--- /dev/null
+++ b/e2e/result-cache-restore-without-reflection/composer.json
@@ -0,0 +1,24 @@
+{
+    "require-dev": {
+        "phpstan/phpstan-symfony": "@dev",
+        "phpstan/extension-installer": "^1.4",
+        "phpstan/phpstan-doctrine": "@dev",
+        "phpstan/phpstan-beberlei-assert": "@dev",
+        "phpstan/phpstan-phpunit": "@dev",
+        "phpstan/phpstan-webmozart-assert": "@dev",
+        "phpstan/phpstan-mockery": "@dev",
+        "phpstan/phpstan-nette": "@dev",
+        "phpstan/phpstan-dibi": "@dev",
+        "php-standard-library/phpstan-extension": "@dev"
+    },
+	"autoload": {
+		"classmap": [
+			"lib/"
+		]
+	},
+    "config": {
+        "allow-plugins": {
+            "phpstan/extension-installer": true
+        }
+    }
+}
diff --git a/e2e/result-cache-restore-without-reflection/lib/ThrowingSourceLocator.php b/e2e/result-cache-restore-without-reflection/lib/ThrowingSourceLocator.php
new file mode 100644
index 00000000000..197e78e755d
--- /dev/null
+++ b/e2e/result-cache-restore-without-reflection/lib/ThrowingSourceLocator.php
@@ -0,0 +1,25 @@
+<?php declare(strict_types = 1);
+
+namespace E2EFixture;
+
+use LogicException;
+use PHPStan\BetterReflection\Identifier\Identifier;
+use PHPStan\BetterReflection\Identifier\IdentifierType;
+use PHPStan\BetterReflection\Reflection\Reflection;
+use PHPStan\BetterReflection\Reflector\Reflector;
+use PHPStan\BetterReflection\SourceLocator\Type\SourceLocator;
+
+final class ThrowingSourceLocator implements SourceLocator
+{
+
+	public function locateIdentifier(Reflector $reflector, Identifier $identifier): ?Reflection
+	{
+		throw new LogicException('SourceLocator::locateIdentifier must not be called during result cache construction');
+	}
+
+	public function locateIdentifiersByType(Reflector $reflector, IdentifierType $identifierType): array
+	{
+		throw new LogicException('SourceLocator::locateIdentifiersByType must not be called during result cache construction');
+	}
+
+}
diff --git a/e2e/result-cache-restore-without-reflection/phpstan.neon b/e2e/result-cache-restore-without-reflection/phpstan.neon
new file mode 100644
index 00000000000..96c80e517ca
--- /dev/null
+++ b/e2e/result-cache-restore-without-reflection/phpstan.neon
@@ -0,0 +1,10 @@
+parameters:
+	level: 8
+	paths:
+		- src
+
+services:
+	betterReflectionSourceLocator:
+		class: PHPStan\BetterReflection\SourceLocator\Type\SourceLocator
+		factory: E2EFixture\ThrowingSourceLocator
+		autowired: false
diff --git a/e2e/result-cache-restore-without-reflection/src/foo.php b/e2e/result-cache-restore-without-reflection/src/foo.php
new file mode 100644
index 00000000000..83d9c120c76
--- /dev/null
+++ b/e2e/result-cache-restore-without-reflection/src/foo.php
@@ -0,0 +1,4 @@
+<?php
+
+echo "";
+
diff --git a/src/Node/Expr/AlwaysRememberedExpr.php b/src/Node/Expr/AlwaysRememberedExpr.php
index 71f40b97244..f389fac356b 100644
--- a/src/Node/Expr/AlwaysRememberedExpr.php
+++ b/src/Node/Expr/AlwaysRememberedExpr.php
@@ -7,6 +7,7 @@
 use PHPStan\Node\VirtualNode;
 use PHPStan\Type\Type;
 
+/** Wraps an expression so its type is always remembered in the scope, bypassing impurity checks. */
 final class AlwaysRememberedExpr extends Expr implements VirtualNode
 {
 
diff --git a/src/Type/Php/ClassExistsFunctionTypeSpecifyingExtension.php b/src/Type/Php/ClassExistsFunctionTypeSpecifyingExtension.php
index 8265a598b1f..06c1aad5937 100644
--- a/src/Type/Php/ClassExistsFunctionTypeSpecifyingExtension.php
+++ b/src/Type/Php/ClassExistsFunctionTypeSpecifyingExtension.php
@@ -12,7 +12,9 @@
 use PHPStan\Analyser\TypeSpecifierAwareExtension;
 use PHPStan\Analyser\TypeSpecifierContext;
 use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Node\Expr\AlwaysRememberedExpr;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\BooleanType;
 use PHPStan\Type\ClassStringType;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\Constant\ConstantStringType;
@@ -47,10 +49,11 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 		$args = $node->getArgs();
 		$argType = $scope->getType($args[0]->value);
 		if ($argType instanceof ConstantStringType) {
+			$funcCall = new FuncCall(new FullyQualified('class_exists'), [
+				new Arg(new String_(ltrim($argType->getValue(), '\\'))),
+			]);
 			return $this->typeSpecifier->create(
-				new FuncCall(new FullyQualified('class_exists'), [
-					new Arg(new String_(ltrim($argType->getValue(), '\\'))),
-				]),
+				new AlwaysRememberedExpr($funcCall, new BooleanType(), new BooleanType()),
 				new ConstantBooleanType(true),
 				$context,
 				$scope,
diff --git a/tests/PHPStan/Analyser/data/do-not-remember-possibly-impure-function-values.php b/tests/PHPStan/Analyser/data/do-not-remember-possibly-impure-function-values.php
index 5adbbc52200..158ab83dec7 100644
--- a/tests/PHPStan/Analyser/data/do-not-remember-possibly-impure-function-values.php
+++ b/tests/PHPStan/Analyser/data/do-not-remember-possibly-impure-function-values.php
@@ -109,3 +109,50 @@ function test(): void
 		assertType('int', impure());
 	}
 }
+
+function testClassExistsRemembered(): void
+{
+	if (\class_exists('Bug8579RememberedA')) {
+		assertType('true', \class_exists('Bug8579RememberedA'));
+	} else {
+		assertType('bool', \class_exists('Bug8579RememberedA'));
+	}
+
+	assertType('bool', \class_exists('Bug8579RememberedA'));
+}
+
+function testClassExistsFalseNotRemembered(): void
+{
+	if (!\class_exists('Bug8579FalseNotRememberedA')) {
+		assertType('bool', \class_exists('Bug8579FalseNotRememberedA'));
+	}
+
+	assertType('bool', \class_exists('Bug8579FalseNotRememberedA'));
+}
+
+function testInterfaceExistsFalseNotRemembered(): void
+{
+	if (!\interface_exists('Bug8579FalseNotRememberedC')) {
+		assertType('bool', \interface_exists('Bug8579FalseNotRememberedC'));
+	}
+
+	assertType('bool', \interface_exists('Bug8579FalseNotRememberedC'));
+}
+
+function testTraitExistsFalseNotRemembered(): void
+{
+	if (!\trait_exists('Bug8579FalseNotRememberedD')) {
+		assertType('bool', \trait_exists('Bug8579FalseNotRememberedD'));
+	}
+
+	assertType('bool', \trait_exists('Bug8579FalseNotRememberedD'));
+}
+
+function testEnumExistsFalseNotRemembered(): void
+{
+	if (!\enum_exists('Bug8579FalseNotRememberedE')) {
+		assertType('bool', \enum_exists('Bug8579FalseNotRememberedE'));
+	}
+
+	assertType('bool', \enum_exists('Bug8579FalseNotRememberedE'));
+}
diff --git a/tests/PHPStan/Rules/Classes/InstantiationDoNotRememberPossiblyImpureValuesRuleTest.php b/tests/PHPStan/Rules/Classes/InstantiationDoNotRememberPossiblyImpureValuesRuleTest.php
new file mode 100644
index 00000000000..d40092f3932
--- /dev/null
+++ b/tests/PHPStan/Rules/Classes/InstantiationDoNotRememberPossiblyImpureValuesRuleTest.php
@@ -0,0 +1,35 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Classes;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use function array_merge;
+
+/**
+ * @extends RuleTestCase<InstantiationRule>
+ */
+class InstantiationDoNotRememberPossiblyImpureValuesRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return self::getContainer()->getByType(InstantiationRule::class);
+	}
+
+	public function testBug8579(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-8579.php'], []);
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return array_merge(
+			parent::getAdditionalConfigFiles(),
+			[
+				__DIR__ . '/doNotRememberPossiblyImpureValues.neon',
+			],
+		);
+	}
+
+}
diff --git a/tests/PHPStan/Rules/Classes/data/bug-8579.php b/tests/PHPStan/Rules/Classes/data/bug-8579.php
new file mode 100644
index 00000000000..018ab54678c
--- /dev/null
+++ b/tests/PHPStan/Rules/Classes/data/bug-8579.php
@@ -0,0 +1,13 @@
+<?php
+
+if (!class_exists('NonexistentClassBug8579')) throw new \Exception('nonexistentclass');
+$x = new \NonexistentClassBug8579();
+
+if (!interface_exists('NonexistentInterfaceBug8579')) throw new \Exception('nonexistentinterface');
+$x = new \NonexistentInterfaceBug8579();
+
+if (!trait_exists('NonexistentTraitBug8579')) throw new \Exception('nonexistenttrait');
+$x = new \NonexistentTraitBug8579();
+
+if (!enum_exists('NonexistentEnumBug8579')) throw new \Exception('nonexistentenum');
+$x = new \NonexistentEnumBug8579();
diff --git a/tests/PHPStan/Rules/Classes/doNotRememberPossiblyImpureValues.neon b/tests/PHPStan/Rules/Classes/doNotRememberPossiblyImpureValues.neon
new file mode 100644
index 00000000000..971a1184f48
--- /dev/null
+++ b/tests/PHPStan/Rules/Classes/doNotRememberPossiblyImpureValues.neon
@@ -0,0 +1,2 @@
+parameters:
+	rememberPossiblyImpureFunctionValues: false