[scudo][standalone] Optimization pass

Summary:
This introduces a bunch of small optimizations with the purpose of
making the fastpath tighter:
- tag more conditions as `LIKELY`/`UNLIKELY`: as a rule of thumb we
  consider that every operation related to the secondary is unlikely
- attempt to reduce the number of potentially extraneous instructions
- reorganize the `Chunk` header to not straddle a word boundary and
  use more appropriate types

Note that some `LIKELY`/`UNLIKELY` impact might be less obvious as
they are in slow paths (for example in `secondary.cc`), but at this
point I am throwing a pretty wide net, and it's consistant and doesn't
hurt.

This was mosly done for the benfit of Android, but other platforms
benefit from it too. An aarch64 Android benchmark gives:
- before:
```
  BM_youtube/min_time:15.000/repeats:4/manual_time_mean              445244 us       659385 us            4
  BM_youtube/min_time:15.000/repeats:4/manual_time_median            445007 us       658970 us            4
  BM_youtube/min_time:15.000/repeats:4/manual_time_stddev               885 us         1332 us            4
```
- after:
```
  BM_youtube/min_time:15.000/repeats:4/manual_time_mean       415697 us       621925 us            4
  BM_youtube/min_time:15.000/repeats:4/manual_time_median     415913 us       622061 us            4
  BM_youtube/min_time:15.000/repeats:4/manual_time_stddev        990 us         1163 us            4
```

Additional since `-Werror=conversion` is enabled on some platforms we
are built on, enable it upstream to catch things early: a few sign
conversions had slept through and needed additional casting.

Reviewers: hctim, morehouse, eugenis, vitalybuka

Reviewed By: vitalybuka

Subscribers: srhines, mgorny, javed.absar, kristof.beyls, delcypher, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D64664

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@366918 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 5 deletions

diff --git a/lib/scudo/standalone/primary32.h b/lib/scudo/standalone/primary32.h
index 2b2fa8b3d..10f921a8d 100644
--- a/lib/scudo/standalone/primary32.h
+++ b/lib/scudo/standalone/primary32.h
@@ -74,7 +74,7 @@ public:
       // See comment in the 64-bit primary about releasing smaller size classes.
       Sci->CanRelease = (ReleaseToOsInterval > 0) &&
                         (I != SizeClassMap::BatchClassId) &&
-                        (getSizeByClassId(I) >= (PageSize / 32));
+                        (getSizeByClassId(I) >= (PageSize / 16));
     }
     ReleaseToOsIntervalMs = ReleaseToOsInterval;
   }
@@ -99,9 +99,9 @@ public:
     SizeClassInfo *Sci = getSizeClassInfo(ClassId);
     ScopedLock L(Sci->Mutex);
     TransferBatch *B = Sci->FreeList.front();
-    if (B)
+    if (B) {
       Sci->FreeList.pop_front();
-    else {
+    } else {
       B = populateFreeList(C, ClassId, Sci);
       if (UNLIKELY(!B))
         return nullptr;
@@ -129,7 +129,7 @@ public:
 
   void enable() {
     for (sptr I = static_cast<sptr>(NumClasses) - 1; I >= 0; I--)
-      getSizeClassInfo(I)->Mutex.unlock();
+      getSizeClassInfo(static_cast<uptr>(I))->Mutex.unlock();
   }
 
   template <typename F> void iterateOverBlocks(F Callback) {
@@ -356,7 +356,8 @@ private:
       const s32 IntervalMs = ReleaseToOsIntervalMs;
       if (IntervalMs < 0)
         return;
-      if (Sci->ReleaseInfo.LastReleaseAtNs + IntervalMs * 1000000ULL >
+      if (Sci->ReleaseInfo.LastReleaseAtNs +
+              static_cast<uptr>(IntervalMs) * 1000000ULL >
           getMonotonicTime()) {
         return; // Memory was returned recently.
       }