[compiler-rt] ea42515 - [asan] Faster version of QuickCheckForUnpoisonedRegion

[Vitaly Buka via llvm-commits]

Author: Vitaly Buka
Date: 2022-08-08T22:07:35-07:00
New Revision: ea42515dadfa3ca0020bc7107787761f026ad2dc

URL: https://github.com/llvm/llvm-project/commit/ea42515dadfa3ca0020bc7107787761f026ad2dc
DIFF: https://github.com/llvm/llvm-project/commit/ea42515dadfa3ca0020bc7107787761f026ad2dc.diff

LOG: [asan] Faster version of QuickCheckForUnpoisonedRegion

Slightly helps with performance regression after D128146.

Added: 
    

Modified: 
    compiler-rt/lib/asan/asan_interceptors_memintrinsics.h

Removed: 
    


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diff  --git a/compiler-rt/lib/asan/asan_interceptors_memintrinsics.h b/compiler-rt/lib/asan/asan_interceptors_memintrinsics.h
index 391e72b826d3..bbc5390ceaa4 100644
--- a/compiler-rt/lib/asan/asan_interceptors_memintrinsics.h
+++ b/compiler-rt/lib/asan/asan_interceptors_memintrinsics.h
@@ -26,17 +26,21 @@ namespace __asan {
 // Return true if we can quickly decide that the region is unpoisoned.
 // We assume that a redzone is at least 16 bytes.
 static inline bool QuickCheckForUnpoisonedRegion(uptr beg, uptr size) {
-  if (UNLIKELY(size == 0))
+  if (UNLIKELY(size == 0 || size > sizeof(uptr) * ASAN_SHADOW_GRANULARITY))
+    return !size;
+
+  uptr last = beg + size - 1;
+  uptr shadow_first = MEM_TO_SHADOW(beg);
+  uptr shadow_last = MEM_TO_SHADOW(last);
+  uptr uptr_first = RoundDownTo(shadow_first, sizeof(uptr));
+  uptr uptr_last = RoundDownTo(shadow_last, sizeof(uptr));
+  if (LIKELY(((*reinterpret_cast<const uptr *>(uptr_first) |
+               *reinterpret_cast<const uptr *>(uptr_last)) == 0)))
     return true;
-  if (size <= 32)
-    return !AddressIsPoisoned(beg) && !AddressIsPoisoned(beg + size - 1) &&
-           !AddressIsPoisoned(beg + size / 2);
-  if (size <= 64)
-    return !AddressIsPoisoned(beg) && !AddressIsPoisoned(beg + size / 4) &&
-           !AddressIsPoisoned(beg + size - 1) &&
-           !AddressIsPoisoned(beg + 3 * size / 4) &&
-           !AddressIsPoisoned(beg + size / 2);
-  return false;
+  u8 shadow = AddressIsPoisoned(last);
+  for (; shadow_first < shadow_last; ++shadow_first)
+    shadow |= *((u8 *)shadow_first);
+  return !shadow;
 }
 
 struct AsanInterceptorContext {