[all-commits] [llvm/llvm-project] 5d3f29: [CallPromotionUtils]Implement conditional indirect...

[Mingming Liu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5d3f296733b66281a53dd451a983e69ae0bb482f
      https://github.com/llvm/llvm-project/commit/5d3f296733b66281a53dd451a983e69ae0bb482f
  Author: Mingming Liu <mingmingl at google.com>
  Date:   2024-05-19 (Sun, 19 May 2024)

  Changed paths:
    M llvm/include/llvm/Transforms/Utils/CallPromotionUtils.h
    M llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
    M llvm/unittests/Transforms/Utils/CallPromotionUtilsTest.cpp

  Log Message:
  -----------
  [CallPromotionUtils]Implement conditional indirect call promotion with vtable-based comparison (#81378)

* Given the code sequence
   ```
   bb:
     %vtable = load ptr, ptr %d, !prof !8
     %vfn = getelementptr inbounds ptr, ptr %vtable, i64 1
     %1 = load ptr, ptr %vfn
     %call = tail call i32 %1(ptr %d), !prof !9
  ```
   The transformation looks like

   ```
   bb:
    %vtable = load ptr, ptr %d, align 8
    %vfn = getelementptr inbounds i8, ptr %vtable, i64 8  <-- Inst 1
    %func-addr = load ptr, ptr %vfn, align 8  <-- Inst 2
    # compare loaded pointers with address point of vtables
%1 = icmp eq ptr %vtable, getelementptr inbounds (i8, ptr @_ZTV<VTable>,
i32 16)
br i1 %1, label %if.true.direct_targ, label %if.false.orig_indirect,
!prof !18

  if.true.direct_targ:                              ; preds = %bb
    %2 = tail call i32 @<direct-call>(ptr nonnull %d)
    br label %if.end.icp

  if.false.orig_indirect:                           ; preds = %bb
    %call = tail call i32 %func-addr(ptr nonnull %d)
    br label %if.end.icp

if.end.icp: ; preds = %if.false.orig_indirect, %if.true.direct_targ
%4 = phi i32 [ %call, %if.false.orig_indirect ], [ %2,
%if.true.direct_targ ]

   ```
It's intentional that `Inst 1` and `Inst2` remains in `bb` (not in
`if.false.orig_indirect`). A follow up patch will implement code to sink
them (something like how `instcombine` would
[sink](https://github.com/llvm/llvm-project/blob/2fcfc9754a16805b81e541dc8222a8b5cf17a121/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp#L4293)
instructions along with [debug
intrinsics](https://github.com/llvm/llvm-project/blob/2fcfc9754a16805b81e541dc8222a8b5cf17a121/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp#L4356-L4368)
if possible)

* The parent patch is https://github.com/llvm/llvm-project/pull/81181



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications