[PATCH] D57129: [SimpleLoopUnswitch] Early check exit for trivial unswitch with MemorySSA.

[Alina Sbirlea via Phabricator via llvm-commits]

asbirlea created this revision.
asbirlea added a reviewer: chandlerc.
Herald added subscribers: george.burgess.iv, Prazek, jlebar, sanjoy.

If MemorySSA is avaiable, we can skip checking all instructions if block has any Defs.
(volatile loads are also Defs).
We still need to check all instructions for "canThrow", even if no Defs are found.


Repository:
  rL LLVM

https://reviews.llvm.org/D57129

Files:
  lib/Transforms/Scalar/SimpleLoopUnswitch.cpp


Index: lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
===================================================================
--- lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -847,6 +847,10 @@
     // Check if there are any side-effecting instructions (e.g. stores, calls,
     // volatile loads) in the part of the loop that the code *would* execute
     // without unswitching.
+    if (MSSAU) // Possible early exit with MSSA
+      if (auto *Defs = MSSAU->getMemorySSA()->getBlockDefs(CurrentBB))
+        if (!isa<MemoryPhi>(*Defs->begin()) || (++Defs->begin() != Defs->end()))
+          return Changed;
     if (llvm::any_of(*CurrentBB,
                      [](Instruction &I) { return I.mayHaveSideEffects(); }))
       return Changed;


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