Re: [PATCH] Remove not needed __builtin_expect due to malloc predictor.

[Jonathan Wakely]

On 10/08/18 12:32 +0200, Martin Liška wrote:

Hi.

After we introduced new non-NULL malloc predictor, we can remove these 
__builtin_expects.
Predictors will change in following way:

Before:

Predictions for bb 5
 first match heuristics: 10.00%
 combined heuristics: 10.00%
 __builtin_expect heuristics of edge 5->6: 10.00%
 call heuristics of edge 5->6 (ignored): 33.00%
 loop exit heuristics of edge 5->9 (ignored): 5.50%

After:

Predictions for bb 5
 first match heuristics: 0.04%
 combined heuristics: 0.04%
 pointer (on trees) heuristics of edge 5->6 (ignored): 30.00%
 malloc returned non-NULL heuristics of edge 5->6: 0.04%
 call heuristics of edge 5->6 (ignored): 33.00%
 loop exit heuristics of edge 5->9 (ignored): 5.50%


Maybe there are similar allocation-related expects, but I haven't found them.
Ready after it survives regression tests?

OK for trunk - thanks!

Martin

libstdc++-v3/ChangeLog:

2018-08-10  Martin Liska  <mli...@suse.cz>

        * libsupc++/new_op.cc (new): Remove __builtin_expect as malloc
       predictor can handle that.
        * libsupc++/new_opa.cc: Likewise.
        * libsupc++/new_opnt.cc (new): Likewise.
---
libstdc++-v3/libsupc++/new_op.cc   | 2 +-
libstdc++-v3/libsupc++/new_opa.cc  | 2 +-
libstdc++-v3/libsupc++/new_opnt.cc | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/libsupc++/new_op.cc b/libstdc++-v3/libsupc++/new_op.cc
index 3a1e38d9df7..3caa0bab2ea 100644
--- a/libstdc++-v3/libsupc++/new_op.cc
+++ b/libstdc++-v3/libsupc++/new_op.cc
@@ -47,7 +47,7 @@ operator new (std::size_t sz) _GLIBCXX_THROW (std::bad_alloc)
  if (sz == 0)
    sz = 1;

-  while (__builtin_expect ((p = malloc (sz)) == 0, false))
+  while ((p = malloc (sz)) == 0)
    {
      new_handler handler = std::get_new_handler ();
      if (! handler)
diff --git a/libstdc++-v3/libsupc++/new_opa.cc 
b/libstdc++-v3/libsupc++/new_opa.cc
index 68eac5b8ceb..a27ff843ca1 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -126,7 +126,7 @@ operator new (std::size_t sz, std::align_val_t al)
#endif

  using __gnu_cxx::aligned_alloc;
-  while (__builtin_expect ((p = aligned_alloc (align, sz)) == 0, false))
+  while ((p = aligned_alloc (align, sz)) == 0)
    {
      new_handler handler = std::get_new_handler ();
      if (! handler)
diff --git a/libstdc++-v3/libsupc++/new_opnt.cc 
b/libstdc++-v3/libsupc++/new_opnt.cc
index a2dc33ad4d3..faab44e66c2 100644
--- a/libstdc++-v3/libsupc++/new_opnt.cc
+++ b/libstdc++-v3/libsupc++/new_opnt.cc
@@ -40,7 +40,7 @@ operator new (std::size_t sz, const std::nothrow_t&) 
_GLIBCXX_USE_NOEXCEPT
  if (sz == 0)
    sz = 1;

-  while (__builtin_expect ((p = malloc (sz)) == 0, false))
+  while ((p = malloc (sz)) == 0)
    {
      new_handler handler = std::get_new_handler ();
      if (! handler)