[clang] [C23] Use thread_local semantics (PR #70107)

[Erich Keane via cfe-commits]

================
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -std=c23 -emit-llvm -o - %s | FileCheck %s
+
+// Ensure that thread_local and _Thread_local emit the same codegen. See
+// https://github.com/llvm/llvm-project/issues/70068 for details.
+
+void func(void) {
+  static thread_local int i = 12;
+  static _Thread_local int j = 13;
+
+  extern thread_local int k;
+  extern thread_local int l;
+
+  (void)k;
+  (void)l;
+}
+
+// CHECK:      @func.i = internal thread_local global i32 12, align 4
+// CHECK-NEXT: @func.j = internal thread_local global i32 13, align 4
+// CHECK-NEXT: @k = external thread_local global i32, align 4
+// CHECK-NEXT: @l = external thread_local global i32, align 4
+
+// CHECK:      define dso_local void @func()
+// CHECK-NEXT: entry:
+// CHECK-NEXT: %0 = call align 4 ptr @llvm.threadlocal.address.p0(ptr align 4 @k)
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erichkeane wrote:

for the %0-3 you probably want to do wildcards, since these can sometimes end up with 'names' depending on your config.  The rest I think are all ok.

https://github.com/llvm/llvm-project/pull/70107