Swift Optimizer: add the StackProtection optimization

It decides which functions need stack protection.

It sets the `needStackProtection` flags on all function which contain stack-allocated values for which an buffer overflow could occur.

Within safe swift code there shouldn't be any buffer overflows.
But if the address of a stack variable is converted to an unsafe pointer, it's not in the control of the compiler anymore.
This means, if there is any `address_to_pointer` instruction for an `alloc_stack`, such a function is marked for stack protection.
Another case is `index_addr` for non-tail allocated memory.
This pattern appears if pointer arithmetic is done with unsafe pointers in swift code.

If the origin of an unsafe pointer can only be tracked to a function argument, the pass tries to find the root stack allocation for such an argument by doing an inter-procedural analysis.
If this is not possible, the fallback is to move the argument into a temporary `alloc_stack` and do the unsafe pointer operations on the temporary.

rdar://93677524

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/CMakeLists.txt

@@ -15,6 +15,7 @@ add_subdirectory(Analysis)
 add_subdirectory(DataStructures)
 add_subdirectory(InstructionPasses)
 add_subdirectory(PassManager)
+add_subdirectory(ModulePasses)
 add_subdirectory(FunctionPasses)
 add_subdirectory(TestPasses)
 add_subdirectory(Utilities)

SwiftCompilerSources/Sources/Optimizer/ModulePasses/CMakeLists.txt

@@ -0,0 +1,11 @@
+# This source file is part of the Swift.org open source project
+#
+# Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See http://swift.org/LICENSE.txt for license information
+# See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+
+swift_compiler_sources(Optimizer
+  StackProtection.swift
+)