[PATCH] D12013: [InstCombineCasts] Add cost model to decide which truncates are worth removing

[hfinkel@anl.gov via llvm-commits]

hfinkel added a subscriber: hfinkel.

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Comment at: lib/Transforms/InstCombine/InstCombineCasts.cpp:341
@@ +340,3 @@
+/// and store it into the "Cost" argument.
+/// Currently cost model is simple - increase cost by one for each additional
+/// instruction required, decrease cost by one for each instruction that
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Currently cost model is simple -> Currently, the cost model is simple

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Comment at: lib/Transforms/InstCombine/InstCombineCasts.cpp:457
@@ +456,3 @@
+  // This is not a recognized instruction, but we can always truncate it by
+  // adding additional explicit trunc.
+  Cost += 1;
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This does not seem right. Arbitrary instructions don't commute with truncation, by which I mean trunc(arbitrary(x, y)) != arbitrary(trunc(x), trunc(y)) in general. Also, for many instructions you'd hit the llvm_unreachable in the default case in EvaluateInDifferentType.




Repository:
  rL LLVM

http://reviews.llvm.org/D12013