Add a prototype of a new peephole optimizing pass that uses LazyValue info to simplify PHIs and select's.

This pass addresses the missed optimizations from PR2581 and PR4420.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112325 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/ValuePropagation/phi.ll

@@ -0,0 +1,17 @@
+; RUN: opt < %s -value-propagation -S | FileCheck %s
+; PR2581
+
+; CHECK: @run
+define i32 @run(i1 %C) nounwind  {
+        br i1 %C, label %exit, label %body
+
+body:           ; preds = %0
+; CHECK-NOT: select
+        %A = select i1 %C, i32 10, i32 11               ; <i32> [#uses=1]
+; CHECK: ret i32 11
+        ret i32 %A
+
+exit:           ; preds = %0
+; CHECK: ret i32 10
+        ret i32 10
+}