bolt/test/X86/shrinkwrapping-do-not-pessimize.s

   1 # This checks that shrink wrapping does not pessimize a CFG pattern where two
   2 # blocks can be proved to have the same execution count but, because of profile
   3 # inaccuricies, we could move saves into the second block. We can prove two
   4 # blocks have the same frequency when B post-dominate A and A dominates B and
   5 # are at the same loop nesting level. This would be a pessimization because
   6 # shrink wrapping is unlikely to be able to cleanly move PUSH instructions,
   7 # inserting additional store instructions.
   8
   9 # REQUIRES: system-linux
  10
  11 # RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown \
  12 # RUN:   %s -o %t.o
  13 # RUN: link_fdata %s %t.o %t.fdata
  14 # RUN: llvm-strip --strip-unneeded %t.o
  15 # RUN: %clang %cflags %t.o -o %t.exe -Wl,-q -nostdlib
  16 # RUN: llvm-bolt -relocs %t.exe -o %t.out -data %t.fdata \
  17 # RUN:     -frame-opt=all -equalize-bb-counts | FileCheck %s
  18
  19 # Here we create a CFG pattern with two blocks A and B belonging to the same
  20 # equivalency class as defined by dominance relations and having in theory
  21 # the same frequency. But we tweak edge counts from profile to make block A
  22 # hotter than block B.
  23   .globl _start
  24   .type _start, %function
  25 _start:
  26   .cfi_startproc
  27 # Hot prologue
  28 # FDATA: 0 [unknown] 0 1 _start 0 0 10
  29   push  %rbp
  30   mov   %rsp, %rbp
  31   push  %rbx
  32   push  %r14
  33   subq  $0x20, %rsp
  34 b:  je  end_if_1
  35 # FDATA: 1 _start #b# 1 _start #end_if_1# 0 1
  36 if_false:
  37   movq rel(%rip), %rdi  # Add this to create a relocation and run bolt w/ relocs
  38 c:  jmp end_if_1
  39 # Reduce frequency from 9 to 1 to simulate an inaccurate profile
  40 # FDATA: 1 _start #c# 1 _start #end_if_1# 0 1
  41 end_if_1:
  42   # first uses of R14 and RBX appear at this point, possible move point for SW
  43   mov %r14, %rdi
  44   mov %rbx, %rdi
  45   leaq -0x20(%rbp), %r14
  46   movq -0x20(%rbp), %rdi
  47   addq  $0x20, %rsp
  48   pop %r14
  49   pop %rbx
  50   pop %rbp
  51   ret
  52   .cfi_endproc
  53   .size _start, .-_start
  54
  55   .data
  56 rel:  .quad end_if_1
  57
  58 # CHECK:   BOLT-INFO: Shrink wrapping moved 0 spills inserting load/stores and 0 spills inserting push/pops