[clang] [CIR] Add transform test for cir-flatten-cfg (PR #130861)

[Erich Keane via cfe-commits]

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@@ -0,0 +1,58 @@
+// RUN: cir-opt %s -cir-flatten-cfg -o - | FileCheck %s
+
+module {
+  cir.func @foo() {
+    cir.scope {
+      %0 = cir.alloca !cir.int<u, 32>, !cir.ptr<!cir.int<u, 32>>, ["a", init] {alignment = 4 : i64}
+      %1 = cir.const #cir.int<4> : !cir.int<u, 32>
+      cir.store %1, %0 : !cir.int<u, 32>, !cir.ptr<!cir.int<u, 32>>
+    }
+    cir.return
+  }
+// CHECK:  cir.func @foo() {
+// CHECK:    cir.br ^bb1
----------------
erichkeane wrote:

This here is a touch awkward, right?  I know we did a bit of work to remove 'empty' blocks in the pass.  I wonder if a future version of this pass should be checking the 'exit' of a block to see if it is a single-out (that is, no decisions being done, just a single `br`, and merge the two.  It seems to fit in well with the flatten.

That is, this function here seems like it should/could be a single block, right?

https://github.com/llvm/llvm-project/pull/130861