Add a unprotectedStackAlloc builtin

It's like `Builtin.stackAlloc`, but doesn't set the `[stack_protection]` flag on its containing function.

Author: eeckstein

include/swift/AST/Builtins.def

@@ -629,6 +629,10 @@ BUILTIN_MISC_OPERATION(DeallocRaw, "deallocRaw", "", Special)
 /// is not known at compile time, MaximumAlignment is assumed.
 BUILTIN_MISC_OPERATION(StackAlloc, "stackAlloc", "", Special)
 
+/// Like `stackAlloc`, but doesn't set the `[stack_protection]` flag on its
+/// containing function.
+BUILTIN_MISC_OPERATION(UnprotectedStackAlloc, "unprotectedStackAlloc", "", Special)
+
 /// StackDealloc has type (Builtin.RawPointer) -> ()
 ///
 /// Parameters: address.

include/swift/Basic/Features.def

@@ -82,6 +82,7 @@ LANGUAGE_FEATURE(BuiltinBuildMainExecutor, 0, "MainActor executor building built
 LANGUAGE_FEATURE(BuiltinCreateAsyncTaskInGroup, 0, "MainActor executor building builtin", true)
 LANGUAGE_FEATURE(BuiltinCopy, 0, "Builtin.copy()", true)
 LANGUAGE_FEATURE(BuiltinStackAlloc, 0, "Builtin.stackAlloc", true)
+LANGUAGE_FEATURE(BuiltinUnprotectedStackAlloc, 0, "Builtin.unprotectedStackAlloc", true)
 LANGUAGE_FEATURE(BuiltinTaskRunInline, 0, "Builtin.taskRunInline", true)
 LANGUAGE_FEATURE(BuiltinUnprotectedAddressOf, 0, "Builtin.unprotectedAddressOf", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(SpecializeAttributeWithAvailability, 0, "@_specialize attribute with availability", true)

lib/AST/ASTPrinter.cpp

@@ -3020,6 +3020,10 @@ static bool usesFeatureBuiltinStackAlloc(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureBuiltinUnprotectedStackAlloc(Decl *decl) {
+  return false;
+}
+
 static bool usesFeatureBuiltinAssumeAlignment(Decl *decl) {
   return false;
 }

lib/AST/Builtins.cpp

@@ -2707,6 +2707,7 @@ ValueDecl *swift::getBuiltinValueDecl(ASTContext &Context, Identifier Id) {
     return getDeallocOperation(Context, Id);
 
   case BuiltinValueKind::StackAlloc:
+  case BuiltinValueKind::UnprotectedStackAlloc:
     return getStackAllocOperation(Context, Id);
   case BuiltinValueKind::StackDealloc:
     return getStackDeallocOperation(Context, Id);

lib/IRGen/IRGenSIL.cpp

@@ -3237,7 +3237,8 @@ static Alignment getStackAllocationAlignment(IRGenSILFunction &IGF,
 /// some other builtin.)
 static bool emitStackAllocBuiltinCall(IRGenSILFunction &IGF,
                                       swift::BuiltinInst *i) {
-  if (i->getBuiltinKind() == BuiltinValueKind::StackAlloc) {
+  if (i->getBuiltinKind() == BuiltinValueKind::StackAlloc ||
+      i->getBuiltinKind() == BuiltinValueKind::UnprotectedStackAlloc) {
     // Stack-allocate a buffer with the specified size/alignment.
     auto loc = i->getLoc().getSourceLoc();
     auto size = getStackAllocationSize(

lib/SIL/IR/OperandOwnership.cpp

@@ -783,6 +783,7 @@ BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, SRem)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, GenericSRem)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, SSubOver)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, StackAlloc)
+BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, UnprotectedStackAlloc)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, StackDealloc)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, SToSCheckedTrunc)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, SToUCheckedTrunc)

lib/SIL/IR/SILInstruction.cpp

@@ -1243,7 +1243,8 @@ bool SILInstruction::isAllocatingStack() const {
     return PA->isOnStack();
 
   if (auto *BI = dyn_cast<BuiltinInst>(this)) {
-    if (BI->getBuiltinKind() == BuiltinValueKind::StackAlloc) {
+    if (BI->getBuiltinKind() == BuiltinValueKind::StackAlloc ||
+        BI->getBuiltinKind() == BuiltinValueKind::UnprotectedStackAlloc) {
       return true;
     }
   }

lib/SIL/IR/ValueOwnership.cpp

@@ -498,6 +498,7 @@ CONSTANT_OWNERSHIP_BUILTIN(None, AllocRaw)
 CONSTANT_OWNERSHIP_BUILTIN(None, AssertConf)
 CONSTANT_OWNERSHIP_BUILTIN(None, UToSCheckedTrunc)
 CONSTANT_OWNERSHIP_BUILTIN(None, StackAlloc)
+CONSTANT_OWNERSHIP_BUILTIN(None, UnprotectedStackAlloc)
 CONSTANT_OWNERSHIP_BUILTIN(None, StackDealloc)
 CONSTANT_OWNERSHIP_BUILTIN(None, SToSCheckedTrunc)
 CONSTANT_OWNERSHIP_BUILTIN(None, SToUCheckedTrunc)

lib/SIL/Utils/MemAccessUtils.cpp

@@ -2519,6 +2519,7 @@ static void visitBuiltinAddress(BuiltinInst *builtin,
     case BuiltinValueKind::AllocRaw:
     case BuiltinValueKind::DeallocRaw:
     case BuiltinValueKind::StackAlloc:
+    case BuiltinValueKind::UnprotectedStackAlloc:
     case BuiltinValueKind::StackDealloc:
     case BuiltinValueKind::Fence:
     case BuiltinValueKind::StaticReport:

lib/SILOptimizer/Transforms/AccessEnforcementReleaseSinking.cpp

@@ -153,6 +153,7 @@ static bool isBarrier(SILInstruction *inst) {
     case BuiltinValueKind::CreateTaskGroupWithFlags:
     case BuiltinValueKind::DestroyTaskGroup:
     case BuiltinValueKind::StackAlloc:
+    case BuiltinValueKind::UnprotectedStackAlloc:
     case BuiltinValueKind::StackDealloc:
     case BuiltinValueKind::AssumeAlignment:
       return false;