[compiler-rt] 180b99c - [scudo] Relax MemtagTag.SelectRandomTag. (#68048)

[via llvm-commits]

Author: Evgenii Stepanov
Date: 2023-11-09T13:14:20-08:00
New Revision: 180b99c3027f0e26a0d9874b32569d58d109bafe

URL: https://github.com/llvm/llvm-project/commit/180b99c3027f0e26a0d9874b32569d58d109bafe
DIFF: https://github.com/llvm/llvm-project/commit/180b99c3027f0e26a0d9874b32569d58d109bafe.diff

LOG: [scudo] Relax MemtagTag.SelectRandomTag. (#68048)

As it turns out, PRNGs have varying quality.
Relax the test to accept less-then-perfect tag distribution.

Added: 
    

Modified: 
    compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp

Removed: 
    


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diff  --git a/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp b/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
index 2488e04856bd972..fd277f962a9aaac 100644
--- a/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
@@ -120,7 +120,15 @@ TEST_F(MemtagTest, SelectRandomTag) {
     uptr Tags = 0;
     for (uptr I = 0; I < 100000; ++I)
       Tags = Tags | (1u << extractTag(selectRandomTag(Ptr, 0)));
-    EXPECT_EQ(0xfffeull, Tags);
+    // std::popcnt is C++20
+    int PopCnt = 0;
+    while (Tags) {
+      PopCnt += Tags & 1;
+      Tags >>= 1;
+    }
+    // Random tags are not always very random, and this test is not about PRNG
+    // quality.  Anything above half would be satisfactory.
+    EXPECT_GE(PopCnt, 8);
   }
 }