LVI: Recognize the form instcombine canonicalizes range checks into when forming constant ranges.

This could probably be made a lot smarter, but this is a common case and doesn't require LVI to scan a lot
of code. With this change CVP can optimize away the "shift == 0" case in Hashing.h that only gets hit when
"shift" is in a range not containing 0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151919 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/CorrelatedValuePropagation/range.ll

@@ -0,0 +1,43 @@
+; RUN: opt -correlated-propagation -S < %s | FileCheck %s
+
+declare i32 @foo()
+
+define i32 @test1(i32 %a) nounwind {
+  %a.off = add i32 %a, -8
+  %cmp = icmp ult i32 %a.off, 8
+  br i1 %cmp, label %then, label %else
+
+then:
+  %dead = icmp eq i32 %a, 7
+  br i1 %dead, label %end, label %else
+
+else:
+  ret i32 1
+
+end:
+  ret i32 2
+
+; CHECK: @test1
+; CHECK: then:
+; CHECK-NEXT: br i1 false, label %end, label %else
+}
+
+define i32 @test2(i32 %a) nounwind {
+  %a.off = add i32 %a, -8
+  %cmp = icmp ult i32 %a.off, 8
+  br i1 %cmp, label %then, label %else
+
+then:
+  %dead = icmp ugt i32 %a, 15
+  br i1 %dead, label %end, label %else
+
+else:
+  ret i32 1
+
+end:
+  ret i32 2
+
+; CHECK: @test2
+; CHECK: then:
+; CHECK-NEXT: br i1 false, label %end, label %else
+}