Add a helper to remove a branch and DCE the condition, and use it

consistently for deleting branches.  In addition to being slightly 
more readable, this makes SimplifyCFG a bit better 
about cleaning up after itself when it makes conditions unused.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61100 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/SimplifyCFG/2008-12-16-DCECond.ll

@@ -0,0 +1,46 @@
+; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | not grep icmp
+; ModuleID = '/tmp/x.bc'
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i686-pc-linux-gnu"
+
+define i32 @x(i32 %x) {
+entry:
+	%cmp = icmp eq i32 %x, 8		; <i1> [#uses=1]
+	br i1 %cmp, label %ifthen, label %ifend
+
+ifthen:		; preds = %entry
+	%call = call i32 (...)* @foo()		; <i32> [#uses=0]
+	br label %ifend
+
+ifend:		; preds = %ifthen, %entry
+	%cmp2 = icmp ne i32 %x, 8		; <i1> [#uses=1]
+	br i1 %cmp2, label %ifthen3, label %ifend5
+
+ifthen3:		; preds = %ifend
+	%call4 = call i32 (...)* @foo()		; <i32> [#uses=0]
+	br label %ifend5
+
+ifend5:		; preds = %ifthen3, %ifend
+	%cmp7 = icmp eq i32 %x, 9		; <i1> [#uses=1]
+	br i1 %cmp7, label %ifthen8, label %ifend10
+
+ifthen8:		; preds = %ifend5
+	%call9 = call i32 (...)* @bar()		; <i32> [#uses=0]
+	br label %ifend10
+
+ifend10:		; preds = %ifthen8, %ifend5
+	%cmp12 = icmp ne i32 %x, 9		; <i1> [#uses=1]
+	br i1 %cmp12, label %ifthen13, label %ifend15
+
+ifthen13:		; preds = %ifend10
+	%call14 = call i32 (...)* @bar()		; <i32> [#uses=0]
+	br label %ifend15
+
+ifend15:		; preds = %ifthen13, %ifend10
+	ret i32 0
+}
+
+declare i32 @foo(...)
+
+declare i32 @bar(...)
+