make jump threading handle lexically identical compare instructions

as if they were multiple uses of the same instruction.  This interacts
well with the existing loadpre that j-t does to open up many new jump
threads earlier.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73768 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/JumpThreading/dup-cond.ll

@@ -0,0 +1,30 @@
+; RUN: llvm-as < %s | opt -jump-threading -die | llvm-dis | grep icmp | count 1
+
+declare void @f1()
+declare void @f2()
+declare void @f3()
+
+define i32 @test(i32 %A) {
+	%tmp455 = icmp eq i32 %A, 42
+	br i1 %tmp455, label %BB1, label %BB2
+        
+BB2:
+	call void @f1()
+	br label %BB1
+        
+
+BB1:
+	%tmp459 = icmp eq i32 %A, 42
+	br i1 %tmp459, label %BB3, label %BB4
+
+BB3:
+	call void @f2()
+        ret i32 3
+
+BB4:
+	call void @f3()
+	ret i32 4
+}
+
+
+