[llvm] r330301 - Fix data race in X86FloatingPoint.cpp ASSERT_SORTED

[Bob Haarman via llvm-commits]

Author: inglorion
Date: Wed Apr 18 16:04:09 2018
New Revision: 330301

URL: http://llvm.org/viewvc/llvm-project?rev=330301&view=rev
Log:
Fix data race in X86FloatingPoint.cpp ASSERT_SORTED

Summary:
ASSERT_SORTED checks if a table is sorted, and uses a boolean to
prevent the check from being run again if it was earlier determined
that the table is in fact sorted. Unsynchronized reads and writes of
that boolean triggered ThreadSanitizer's data race detection. This
change rewrites the code to use std::atomic<bool> instead.

Fixes PR36922.

Reviewers: rnk

Reviewed By: rnk

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D45742

Modified:
    llvm/trunk/lib/Target/X86/X86FloatingPoint.cpp

Modified: llvm/trunk/lib/Target/X86/X86FloatingPoint.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FloatingPoint.cpp?rev=330301&r1=330300&r2=330301&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86FloatingPoint.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86FloatingPoint.cpp Wed Apr 18 16:04:09 2018
@@ -599,13 +599,14 @@ static int Lookup(ArrayRef<TableEntry> T
 #ifdef NDEBUG
 #define ASSERT_SORTED(TABLE)
 #else
-#define ASSERT_SORTED(TABLE)                                              \
-  { static bool TABLE##Checked = false;                                   \
-    if (!TABLE##Checked) {                                                \
-       assert(std::is_sorted(std::begin(TABLE), std::end(TABLE)) &&       \
-              "All lookup tables must be sorted for efficient access!");  \
-       TABLE##Checked = true;                                             \
-    }                                                                     \
+#define ASSERT_SORTED(TABLE)                                                   \
+  {                                                                            \
+    static std::atomic<bool> TABLE##Checked(false);                            \
+    if (!TABLE##Checked.load(std::memory_order_relaxed)) {                     \
+      assert(std::is_sorted(std::begin(TABLE), std::end(TABLE)) &&             \
+             "All lookup tables must be sorted for efficient access!");        \
+      TABLE##Checked.store(true, std::memory_order_relaxed);                   \
+    }                                                                          \
   }
 #endif