new testcase for a simple optimization that simplifycfg is about to do.

All CFG edges to DEAD should be eliminated.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20299 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/SimplifyCFG/switch_thread.ll

@@ -0,0 +1,78 @@
+; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | not grep 'call void %DEAD'
+
+; Test that we can thread a simple known condition through switch statements.
+
+declare void %foo1()
+declare void %foo2()
+declare void %DEAD()
+
+void %test1(uint %V) {
+        switch uint %V, label %A [
+                 uint 4, label %T
+                 uint 17, label %Done
+                 uint 1234, label %A
+        ]
+
+T:  ;; V == 4 if we get here.
+	call void %foo1()
+        ;; This switch is always statically determined.
+        switch uint %V, label %A2 [
+                 uint 4, label %B
+                 uint 17, label %C
+		 uint 42, label %C
+        ]
+A2:
+	call void %DEAD()
+	call void %DEAD()
+	%cond2 = seteq uint %V, 4    ;; always false
+	br bool %cond2, label %Done, label %C
+
+A:
+	call void %foo1()
+	%cond = setne uint %V, 4    ;; always true
+	br bool %cond, label %Done, label %C
+
+
+Done:
+        ret void
+
+B:
+        call void %foo2()
+	%cond3 = seteq uint %V, 4    ;; always true
+	br bool %cond3, label %Done, label %C
+C:
+	call void %DEAD()
+	ret void
+}
+
+void %test2(uint %V) {
+        switch uint %V, label %A [
+                 uint 4, label %T
+                 uint 17, label %D
+                 uint 1234, label %E
+        ]
+
+A:  ;; V != 4, 17, 1234 here.
+	call void %foo1()
+        ;; This switch is always statically determined.
+        switch uint %V, label %E [
+                 uint 4, label %C
+                 uint 17, label %C
+		 uint 42, label %D
+        ]
+C:
+	call void %DEAD()  ;; unreacahble.
+	ret void
+T:
+	call void %foo1()
+	call void %foo1()
+	ret void
+
+D:
+	call void %foo1()
+	ret void
+
+E:
+        ret void
+}
+