[PATCH] D24315: [CGP] Be less conservative about tail-duplicating a ret to allow tail calls

[Michael Kuperstein via llvm-commits]

mkuper created this revision.
mkuper added reviewers: hansw, rnk, iteratee.
mkuper added a subscriber: llvm-commits.

CGP tail-duplicates rets into blocks that end with a call that feed the ret. This puts the call in tail position, potentially allowing the DAG builder to lower it as a tail call. To avoid the tail-duplication in cases where we won't form the tail call, CGP tries to predict whether this is going to be possible, and avoid doing it when lowering as a tail call will definitely fail. However, it was being too conservative by always throwing away calls to functions with a signext/zeroext attribute on the return type.

Instead, we can use the exact same logic the builder itself uses to determine whether the attributes work out.

https://reviews.llvm.org/D24315

Files:
  include/llvm/CodeGen/Analysis.h
  lib/CodeGen/Analysis.cpp
  lib/CodeGen/CodeGenPrepare.cpp
  test/CodeGen/X86/tailcall-cgp-dup.ll

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