[PATCH] D22782: Added 'inline' attribute to __init to inline the basic_string's constructor

[Laxman Sole via cfe-commits]

laxmansole added a comment.

In https://reviews.llvm.org/D22782#495436, @mclow.lists wrote:

> Do we have a test for the problem that this is solving?


$ cat foo.cpp

  int foo(const std::string name);
  int main(){
      return foo("bar");
  }

$clang++ -S -O3 -fno-exceptions foo.cpp

Assembly output without patch:

  _Z3barv:                                // @_Z3barv
  // BB#0:                                // %entry
      sub sp, sp, #64             // =64
      adrp    x1, .L.str
      add x1, x1, :lo12:.L.str
      add x0, sp, #8              // =8
      orr w2, wzr, #0x3
      stp xzr, x19, [sp, #24]     // 8-byte Folded Spill
      stp x29, x30, [sp, #48]     // 8-byte Folded Spill
      add x29, sp, #48            // =48
      stp xzr, xzr, [sp, #8]
      bl  _ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEPKcm
      add x0, sp, #8              // =8
      bl  _Z3fooNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE
      and w19, w0, #0x1
      add x0, sp, #8              // =8
      bl  _ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev
      mov  w0, w19
      ldp x29, x30, [sp, #48]     // 8-byte Folded Reload
      ldr x19, [sp, #32]          // 8-byte Folded Reload
      add sp, sp, #64             // =64
      ret

Assembly output with path:

  _Z3barv:                                // @_Z3barv
  // BB#0:                                // %entry
      sub sp, sp, #64             // =64
      orr w8, wzr, #0x6
      mov w9, #114
      mov w10, #24930
      add x0, sp, #8              // =8
      stp xzr, x19, [sp, #24]     // 8-byte Folded Spill
      stp x29, x30, [sp, #48]     // 8-byte Folded Spill
      add x29, sp, #48            // =48
      stp xzr, xzr, [sp, #8]
      strb    w8, [sp, #8]
      strb    w9, [sp, #11]
      sturh   w10, [sp, #9]
      strb    wzr, [sp, #12]
      bl  _Z3fooNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE
      and w19, w0, #0x1
      add x0, sp, #8              // =8
      bl  _ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev
      mov  w0, w19
      ldp x29, x30, [sp, #48]     // 8-byte Folded Reload
      ldr x19, [sp, #32]          // 8-byte Folded Reload
      add sp, sp, #64             // =64
      ret

We can see that call to _ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEPKcm get inlined.


https://reviews.llvm.org/D22782