[all-commits] [llvm/llvm-project] f3e1f4: [IVDescriptor] Get the exact FP instruction that d...

[CongzheUalberta via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f3e1f44340dc26e3810d601edf0e052813b7a11c
      https://github.com/llvm/llvm-project/commit/f3e1f44340dc26e3810d601edf0e052813b7a11c
  Author: Congzhe Cao <congzhe.cao at huawei.com>
  Date:   2022-01-27 (Thu, 27 Jan 2022)

  Changed paths:
    M llvm/lib/Analysis/IVDescriptors.cpp
    M llvm/test/Transforms/LoopVectorize/AArch64/strict-fadd.ll

  Log Message:
  -----------
  [IVDescriptor] Get the exact FP instruction that does not allow reordering

This is a bugfix in IVDescriptor.cpp.

The helper function `RecurrenceDescriptor::getExactFPMathInst()`
is supposed to return the 1st FP instruction that does not allow
reordering. However, when constructing the RecurrenceDescriptor,
we trace the use-def chain staring from a PHI node and for each
instruction in the use-def chain, its descriptor overrides the
previous one. Therefore in the final RecurrenceDescriptor we
constructed, we lose previous FP instructions that does not allow
reordering.

Reviewed By: kmclaughlin

Differential Revision: https://reviews.llvm.org/D118073