Avoid duplicating loop header which leads to unnatural loops (and just seem like general badness to me, likely to cause code explosion).

Patch by Florian Brandner.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52223 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/TailDup/2008-06-11-AvoidDupLoopHeader.ll

@@ -0,0 +1,27 @@
+; RUN: llvm-as < %s | opt -tailduplicate -taildup-threshold=3 -stats -disable-output |&
+; RUN:   not grep tailduplicate
+
+define i32 @foo(i32 %l) nounwind  {
+entry:
+	%cond = icmp eq i32 %l, 1		; <i1> [#uses=1]
+	br i1 %cond, label %bb, label %bb9
+
+bb:		; preds = %entry
+	br label %bb9
+
+bb5:		; preds = %bb9
+	%tmp7 = call i32 (...)* @bar( i32 %x.0 ) nounwind 		; <i32> [#uses=1]
+	br label %bb9
+
+bb9:		; preds = %bb5, %bb, %entry
+	%x.0 = phi i32 [ 0, %entry ], [ %tmp7, %bb5 ], [ 1525, %bb ]		; <i32> [#uses=2]
+	%l_addr.0 = phi i32 [ %l, %entry ], [ %tmp11, %bb5 ], [ %l, %bb ]		; <i32> [#uses=1]
+	%tmp11 = add i32 %l_addr.0, -1		; <i32> [#uses=2]
+	%tmp13 = icmp eq i32 %tmp11, -1		; <i1> [#uses=1]
+	br i1 %tmp13, label %bb15, label %bb5
+
+bb15:		; preds = %bb9
+	ret i32 %x.0
+}
+
+declare i32 @bar(...)