[PATCH] D70562: [LiveRegUnits] Add phys_regs_and_masks iterator range (NFC).

[Jin Lin via Phabricator via llvm-commits]

jinlin added a comment.

Hi Florian,

I have encountered a big compile time regression in the machine outlining caused by https://reviews.llvm.org/D70562.

After I backed out the change in D70562 <https://reviews.llvm.org/D70562>, the compile time for the three apps below was back.

I believe the reason is due to the introduction of function phys_regs_and_masks as below.  Originally there is only one loop. With this change, it becomes two loops since it collects the legal operands first. If the filter does not have any effect, it essentially means the loop trip count is doubled.

for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {

>
-

for (const MachineOperand &MOP : phys_regs_and_masks(MI)) {

When I back out the change D70562 <https://reviews.llvm.org/D70562>, I have also made minor changes in file llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp since phys_regs_and_masks is used in that file.

            app1                                               app2                                    app3

Build Time (LLVM 9.0)                                                    4278.512s                                2547.800s                               5917.305s

Build Time (LLVM 10.0)                                                  5625.795s                                4254.092s                                9474.335s

Build Time (LLVM 10.0 + backout D70562 <https://reviews.llvm.org/D70562>)                 4757.243s (+15%)                   2618.070s (+42%)                  6996.272s (+26%)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70562/new/

https://reviews.llvm.org/D70562