tree 92ef2cf89b847e3bf4815af260a502d16654d17e
parent b38c23b4c199221af9e043041f2e594ec1e3745b
author Philip Reames <preames@rivosinc.com> 1743088323 -0700
committer GitHub <noreply@github.com> 1743088323 -0700
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[RISCV] Canonicalize foldable branch conditions in optimizeCondBranch (#132988)

optimizeCondBranch isn't allowed to modify the CFG, but it can rewrite
the branch condition freely. However, If we could fold a conditional
branch to an unconditional one (aside from that restriction), we can
also rewrite it into some canonical conditional branch instead.

Looking at the diffs, the only cases this catches in tree tests are
cases where we could have constant folded during lowering from IR, but
didn't. This is inspired by trying to salvage code from
https://github.com/llvm/llvm-project/pull/131684 which might be useful.
Given the test impact, it's of questionable merits. The main advantage
over only the late cleanup pass is that it kills off the LIs for the
constants early - which can help e.g. register allocation.