[all-commits] [llvm/llvm-project] 911e06: [ICP] Handling must tail calls in indirect call pr...

[Hongtao Yu via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 911e06f5eba66516e87c73d8e76016e549051cd7
      https://github.com/llvm/llvm-project/commit/911e06f5eba66516e87c73d8e76016e549051cd7
  Author: Hongtao Yu <hoy at fb.com>
  Date:   2020-05-03 (Sun, 03 May 2020)

  Changed paths:
    M llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
    A llvm/test/Transforms/PGOProfile/indirect_call_promotion_musttail.ll

  Log Message:
  -----------
  [ICP] Handling must tail calls in indirect call promotion

Per the IR convention, a musttail call must precede a ret with an optional bitcast. This was violated by the indirect call promotion optimization which could result an IR like:

    ; <label>:2192:
      br i1 %2198, label %2199, label %2201, !dbg !226012, !prof !229483

    ; <label>:2199:                                   ; preds = %2192
      musttail call fastcc void @foo(i8* %2195), !dbg !226012
      br label %2202, !dbg !226012

    ; <label>:2201:                                   ; preds = %2192
      musttail call fastcc void %2197(i8* %2195), !dbg !226012
      br label %2202, !dbg !226012

    ; <label>:2202:                                   ; preds = %605, %2201, %2199
      ret void, !dbg !229485

This is being fixed in this change where the return statement goes together with the promoted indirect call. The code generated is like:

    ; <label>:2192:
      br i1 %2198, label %2199, label %2201, !dbg !226012, !prof !229483

    ; <label>:2199:                                   ; preds = %2192
      musttail call fastcc void @foo(i8* %2195), !dbg !226012
      ret void, !dbg !229485

    ; <label>:2201:                                   ; preds = %2192
      musttail call fastcc void %2197(i8* %2195), !dbg !226012
      ret void, !dbg !229485

Differential Revision: https://reviews.llvm.org/D79258