[all-commits] [llvm/llvm-project] 9d2493: Recommit f0c2a5a "[LV] Generalize conditions for s...

[Florian Hahn via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 9d24933f79dd7db3e469b3c4402e076cc41418f7
      https://github.com/llvm/llvm-project/commit/9d24933f79dd7db3e469b3c4402e076cc41418f7
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2019-11-24 (Sun, 24 Nov 2019)

  Changed paths:
    M llvm/lib/Analysis/IVDescriptors.cpp
    M llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
    A llvm/test/Transforms/LoopVectorize/first-order-recurrence-complex.ll
    A llvm/test/Transforms/LoopVectorize/first-order-recurrence-multiply-recurrences.ll

  Log Message:
  -----------
  Recommit f0c2a5a "[LV] Generalize conditions for sinking instrs for first order recurrences."

This version contains 2 fixes for reported issues:
1. Make sure we do not try to sink terminator instructions.
2. Make sure we bail out, if we try to sink an instruction that needs to
   stay in place for another recurrence.

Original message:
If the recurrence PHI node has a single user, we can sink any
instruction without side effects, given that all users are dominated by
the instruction computing the incoming value of the next iteration
('Previous'). We can sink instructions that may cause traps, because
that only causes the trap to occur later, but not on any new paths.

With the relaxed check, we also have to make sure that we do not have a
direct cycle (meaning PHI user == 'Previous), which indicates a
reduction relation, which potentially gets missed by
ReductionDescriptor.

As follow-ups, we can also sink stores, iff they do not alias with
other instructions we move them across and we could also support sinking
chains of instructions and multiple users of the PHI.

Fixes PR43398.

Reviewers: hsaito, dcaballe, Ayal, rengolin

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D69228