Clean up previous cast optimization a bit. Also make zext elimination a bit more aggressive: if it's not necessary to emit an AND (i.e. high bits are already zero), it's profitable to evaluate the operand at a different type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62297 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/cast.ll

@@ -254,3 +254,10 @@ define i1 @test37(i32 %a) {
         ret i1 %e
 }
 
+define i64 @test38(i32 %a) {
+	%1 = icmp eq i32 %a, -2
+	%2 = zext i1 %1 to i8
+	%3 = xor i8 %2, 1
+	%4 = zext i8 %3 to i64
+        ret i64 %4
+}