Use the stack_protector metadata to skip alloca's which don't need protection.

This is the LLVM piece of this work.  The clang work permitted the no_stack_protector
attribute on local variables. That generated new metadata which is used here to
skip any alloca's which would otherwise require a stack protector.

Author: cooperp

llvm/lib/CodeGen/StackProtector.cpp

@@ -431,6 +431,11 @@ bool SSPLayoutAnalysis::requiresStackProtector(Function *F,
   for (const BasicBlock &BB : *F) {
     for (const Instruction &I : BB) {
       if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
+        if (const MDNode *MD = AI->getMetadata("stack-protector")) {
+          const auto *CI = mdconst::dyn_extract<ConstantInt>(MD->getOperand(0));
+          if (CI->isZero())
+            continue;
+        }
         if (AI->isArrayAllocation()) {
           auto RemarkBuilder = [&]() {
             return OptimizationRemark(DEBUG_TYPE, "StackProtectorAllocaOrArray",

llvm/test/CodeGen/AArch64/stack-protector-metadata.ll

@@ -0,0 +1,58 @@
+; RUN: llc -mtriple=aarch64-apple-darwin < %s -o - | FileCheck %s
+
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "arm64-apple-darwin25.1.0"
+
+@.str = private unnamed_addr constant [4 x i8] c"%s\0A\00", align 1
+
+; CHECK-LABEL: test1:
+; CHECK-NOT: ___stack_chk_guard
+
+; Function Attrs: noinline nounwind optnone
+define void @test1(ptr noundef %msg) #0 {
+entry:
+  %msg.addr = alloca ptr, align 8
+  %a = alloca [1000 x i8], align 1, !stack-protector !2
+  store ptr %msg, ptr %msg.addr, align 8
+  %arraydecay = getelementptr inbounds [1000 x i8], ptr %a, i64 0, i64 0
+  %0 = load ptr, ptr %msg.addr, align 8
+  %call = call ptr @strcpy(ptr noundef %arraydecay, ptr noundef %0) #3
+  %arraydecay1 = getelementptr inbounds [1000 x i8], ptr %a, i64 0, i64 0
+  %call2 = call i32 (ptr, ...) @printf(ptr noundef @.str, ptr noundef %arraydecay1)
+  ret void
+}
+
+
+; CHECK-LABEL: test2:
+; CHECK: ___stack_chk_guard
+
+; Function Attrs: noinline nounwind optnone
+define void @test2(ptr noundef %msg) #0 {
+entry:
+  %msg.addr = alloca ptr, align 8
+  %b = alloca [1000 x i8], align 1
+  store ptr %msg, ptr %msg.addr, align 8
+  %arraydecay = getelementptr inbounds [1000 x i8], ptr %b, i64 0, i64 0
+  %0 = load ptr, ptr %msg.addr, align 8
+  %call = call ptr @strcpy(ptr noundef %arraydecay, ptr noundef %0) #3
+  %arraydecay1 = getelementptr inbounds [1000 x i8], ptr %b, i64 0, i64 0
+  %call2 = call i32 (ptr, ...) @printf(ptr noundef @.str, ptr noundef %arraydecay1)
+  ret void
+}
+
+; Function Attrs: nounwind
+declare ptr @strcpy(ptr noundef, ptr noundef) #1
+
+declare i32 @printf(ptr noundef, ...) #2
+
+attributes #0 = { noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" ssp }
+attributes #1 = { nounwind "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+attributes #2 = { "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+attributes #3 = { nounwind }
+
+!llvm.module.flags = !{!0}
+!llvm.ident = !{!1}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{!"clang version 22.0.0"}
+!2 = !{i32 0}