Make GlobalOpt be conservative with TLS variables (PR14309)

For global variables that get the same value stored into them
everywhere, GlobalOpt will replace them with a constant. The problem is
that a thread-local GlobalVariable looks like one value (the address of
the TLS var), but is different between threads.

This patch introduces Constant::isThreadDependent() which returns true
for thread-local variables and constants which depend on them (e.g. a GEP
into a thread-local array), and teaches GlobalOpt not to track such
values.

llvm-svn: 168037

1 files changed, 53 insertions, 0 deletions

diff --git a/llvm/test/Transforms/GlobalOpt/tls.ll b/llvm/test/Transforms/GlobalOpt/tls.ll
new file mode 100644
index 00000000000..7a410e5ed20
--- /dev/null
+++ b/llvm/test/Transforms/GlobalOpt/tls.ll
@@ -0,0 +1,53 @@
+; RUN: opt < %s -globalopt -S | FileCheck %s
+
+declare void @wait()
+declare void @signal()
+declare void @start_thread(void ()*)
+
+@x = internal thread_local global [100 x i32] zeroinitializer, align 16
+@ip = internal global i32* null, align 8
+
+; PR14309: GlobalOpt would think that the value of @ip is always the address of
+; x[1]. However, that address is different for different threads so @ip cannot
+; be replaced with a constant.
+
+define i32 @f() {
+entry:
+  ; Set @ip to point to x[1] for thread 1.
+  store i32* getelementptr inbounds ([100 x i32]* @x, i64 0, i64 1), i32** @ip, align 8
+
+  ; Run g on a new thread.
+  tail call void @start_thread(void ()* @g) nounwind
+  tail call void @wait() nounwind
+
+  ; Reset x[1] for thread 1.
+  store i32 0, i32* getelementptr inbounds ([100 x i32]* @x, i64 0, i64 1), align 4
+
+  ; Read the value of @ip, which now points at x[1] for thread 2.
+  %0 = load i32** @ip, align 8
+
+  %1 = load i32* %0, align 4
+  ret i32 %1
+
+; CHECK: @f
+; Make sure that the load from @ip hasn't been removed.
+; CHECK: load i32** @ip
+; CHECK: ret
+}
+
+define internal void @g() nounwind uwtable {
+entry:
+  ; Set @ip to point to x[1] for thread 2.
+  store i32* getelementptr inbounds ([100 x i32]* @x, i64 0, i64 1), i32** @ip, align 8
+
+  ; Store 50 in x[1] for thread 2.
+  store i32 50, i32* getelementptr inbounds ([100 x i32]* @x, i64 0, i64 1), align 4
+
+  tail call void @signal() nounwind
+  ret void
+
+; CHECK: @g
+; Make sure that the store to @ip hasn't been removed.
+; CHECK: store {{.*}} @ip
+; CHECK: ret
+}