Move a test from cast-set to a new bit-tracking.ll file. Update file comments

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@9674 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/bit-tracking.ll

@@ -0,0 +1,18 @@
+; This file contains various testcases that require tracking whether bits are
+; set or cleared by various instructions.
+
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep %ELIM
+
+; test1 - Eliminating the casts in this testcase (by narrowing the AND 
+; operation) allows instcombine to realize the function always returns false.
+;
+bool %test1(int %A, int %B) {
+        %C1 = setlt int %A, %B
+        %ELIM1 = cast bool %C1 to uint
+        %C2 = setgt int %A, %B
+        %ELIM2 = cast bool %C2 to uint
+        %C3 = and uint %ELIM1, %ELIM2
+        %ELIM3 = cast uint %C3 to bool
+        ret bool %ELIM3
+}
+

test/Transforms/InstCombine/cast-set.ll

@@ -1,7 +1,5 @@
-; I'm not really sure if instcombine should do things like these.  LevelRaise 
-; already sufficiently takes care of these cases, but level raise is really
-; slow.  Might it be better to make there be an instcombine prepass before
-; level raise that takes care of the obvious stuff?
+; This tests for various complex cast elimination cases instcombine should
+; handle.
 
 ; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep cast
 
@@ -18,16 +16,6 @@ bool %test2(int %X, int %Y) {
 	ret bool %c
 }
 
-bool %test3(int %A, int %B) {
-        %cond216 = setlt int %A, %B             ; <bool> [#uses=1]
-        %cst109 = cast bool %cond216 to uint           ; <uint> [#uses=1]
-        %cond219 = setgt int %A, %B             ; <bool> [#uses=1]
-        %cst111 = cast bool %cond219 to uint           ; <uint> [#uses=1]
-        %reg113 = and uint %cst109, %cst111           ; <uint> [#uses=1]
-        %cst222 = cast uint %reg113 to bool             ; <int> [#uses=1]
-        ret bool %cst222
-}
-
 int %test4(int %A) {
 	%B = cast int %A to uint
 	%C = shl uint %B, ubyte 2