Revert "StructurizeCFG: Directly invert cmp instructions"

This reverts commit r300732. This breaks a few tests.
I think the problem is related to adding more uses of
the condition that don't yet exist at this point.

llvm-svn: 301242
diff --git a/llvm/test/CodeGen/AMDGPU/loop_break.ll b/llvm/test/CodeGen/AMDGPU/loop_break.ll
index 84c42e8..b9df2cb 100644
--- a/llvm/test/CodeGen/AMDGPU/loop_break.ll
+++ b/llvm/test/CodeGen/AMDGPU/loop_break.ll
@@ -10,7 +10,7 @@
 
 ; OPT: bb4:
 ; OPT: load volatile
-; OPT: %cmp1 = icmp sge i32 %tmp, %load
+; OPT: xor i1 %cmp1
 ; OPT: call i64 @llvm.amdgcn.if.break(
 ; OPT: br label %Flow