Add 'umax' similar to 'smax' SCEV. Closes PR2003.

Parse reversed smax and umax as smin and umin and express them with negative
or binary-not SCEVs (which are really just subtract under the hood).

Parse 'xor %x, -1' as (-1 - %x).

Remove dead code (ConstantInt::get always returns a ConstantInt).

Don't use getIntegerSCEV(-1, Ty). The first value is an int, then it gets
passed into a uint64_t. Instead, create the -1 directly from
ConstantInt::getAllOnesValue().


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47360 91177308-0d34-0410-b5e6-96231b3b80d8

test/Analysis/ScalarEvolution/2008-02-15-UMax.ll

@@ -0,0 +1,17 @@
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution | grep umax
+; PR2003
+
+define i32 @foo(i32 %n) {
+entry:
+        br label %header
+header:
+        %i = phi i32 [ 100, %entry ], [ %i.inc, %next ]
+        %cond = icmp ult i32 %i, %n
+        br i1 %cond, label %next, label %return
+next:
+        %i.inc = add i32 %i, 1
+        br label %header
+return:
+        ret i32 %i
+}
+