[PATCH] Add a fence elimination pass

[hfinkel at anl.gov]

Have you been able to get compile-time data for large functions yet? We should move this forward unless there are practical problems with the min-cut algorithm.

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Comment at: lib/Target/PowerPC/PPCTargetMachine.cpp:184
@@ +183,3 @@
+    // FIXME: breaks a bunch of brittle tests
+    // addPass(createCFGSimplificationPass());
+  }
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If doing this is generally a good thing, then we should always do it (and on what target would that not be true?).

Otherwise, the CFG simplification pass is mostly a wrapper around the SimplifyCFG utility function, and perhaps it should just be called directly from the FencesPRE pass?

http://reviews.llvm.org/D5758