AST: Promote BuiltinUnprotectedStackAlloc feature to baseline.

Author: tshortli

include/swift/Basic/Features.def

@@ -157,7 +157,7 @@ BASELINE_LANGUAGE_FEATURE(BuiltinCreateAsyncDiscardingTaskInGroup, 0, "Task crea
 BASELINE_LANGUAGE_FEATURE(BuiltinCreateAsyncTaskWithExecutor, 0, "Task create builtin with extra executor preference")
 BASELINE_LANGUAGE_FEATURE(BuiltinCreateAsyncDiscardingTaskInGroupWithExecutor, 0, "Task create in discarding task group with extra executor preference")
 BASELINE_LANGUAGE_FEATURE(BuiltinStackAlloc, 0, "Builtin.stackAlloc")
-LANGUAGE_FEATURE(BuiltinUnprotectedStackAlloc, 0, "Builtin.unprotectedStackAlloc")
+BASELINE_LANGUAGE_FEATURE(BuiltinUnprotectedStackAlloc, 0, "Builtin.unprotectedStackAlloc")
 LANGUAGE_FEATURE(BuiltinAllocVector, 0, "Builtin.allocVector")
 BASELINE_LANGUAGE_FEATURE(BuiltinTaskRunInline, 0, "Builtin.taskRunInline")
 BASELINE_LANGUAGE_FEATURE(BuiltinUnprotectedAddressOf, 0, "Builtin.unprotectedAddressOf")

lib/AST/FeatureSet.cpp

@@ -124,7 +124,6 @@ static bool usesFeatureRethrowsProtocol(Decl *decl) {
   return usesFeatureRethrowsProtocol(decl, checked);
 }
 
-UNINTERESTING_FEATURE(BuiltinUnprotectedStackAlloc)
 UNINTERESTING_FEATURE(BuiltinAllocVector)
 
 static bool usesFeatureNewCxxMethodSafetyHeuristics(Decl *decl) {

stdlib/public/core/TemporaryAllocation.swift

@@ -189,19 +189,11 @@ internal func _withUnprotectedUnsafeTemporaryAllocation<
   // notice and complain.)
   let result: R
 
-#if $BuiltinUnprotectedStackAlloc
   let stackAddress = Builtin.unprotectedStackAlloc(
     capacity._builtinWordValue,
     MemoryLayout<T>.stride._builtinWordValue,
     alignment._builtinWordValue
   )
-#else
-  let stackAddress = Builtin.stackAlloc(
-    capacity._builtinWordValue,
-    MemoryLayout<T>.stride._builtinWordValue,
-    alignment._builtinWordValue
-  )
-#endif
 
   // The multiple calls to Builtin.stackDealloc() are because defer { } produces
   // a child function at the SIL layer and that conflicts with the verifier's