tor-browser

commit cf779e134b734420732099f0c0953365a6c5eee5
parent d2c64cf7da4818155aabf5fca53c686bda14ff69
Author: serge-sans-paille <sguelton@mozilla.com>
Date:   Wed, 22 Oct 2025 08:41:36 +0000

Bug 1993199 - Adjust implementation of mozilla::PodZero r=emilio

As a side effect, also remove unused inclusion of mfbt/PodOperations.h

Differential Revision: https://phabricator.services.mozilla.com/D267933

Diffstat:
M
dom/base/nsWindowMemoryReporter.h
 | 
1
-
M
dom/base/nsWindowSizes.h
 | 
1
-
M
mfbt/PodOperations.h
 | 
22
+++++++++++++---------

3 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/dom/base/nsWindowMemoryReporter.h b/dom/base/nsWindowMemoryReporter.h
@@ -7,7 +7,6 @@
 #ifndef nsWindowMemoryReporter_h__
 #define nsWindowMemoryReporter_h__
 
-#include "mozilla/PodOperations.h"
 #include "mozilla/TimeStamp.h"
 #include "nsIMemoryReporter.h"
 #include "nsIObserver.h"
diff --git a/dom/base/nsWindowSizes.h b/dom/base/nsWindowSizes.h
@@ -8,7 +8,6 @@
 #define nsWindowSizes_h
 
 #include "mozilla/Assertions.h"
-#include "mozilla/PodOperations.h"
 #include "mozilla/SizeOfState.h"
 #include "nsStyleStructList.h"
 
diff --git a/mfbt/PodOperations.h b/mfbt/PodOperations.h
@@ -18,8 +18,10 @@
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
 
-#include <stdint.h>
-#include <string.h>
+#include <cstdint>
+#include <cstring>
+#include <limits>
+#include <type_traits>
 
 namespace mozilla {
 
@@ -43,13 +45,15 @@ static MOZ_ALWAYS_INLINE void PodZero(T* aT, size_t aNElem) {
   static_assert(std::is_trivially_copyable_v<T>,
                 "PodZero requires trivially copyable types");
   /*
-   * This function is often called with 'aNElem' small; we use an inline loop
-   * instead of calling 'memset' with a non-constant length.  The compiler
-   * should inline the memset call with constant size, though.
+   * NB: If the caller uses a constant size, both GCC and Clang inline the
+   * memset call if they find it profitable.
+   *
+   * If the value is dynamic, some might think that it's more profitable to
+   * perform an explicit loop over the aNElem. It turns out Clang rolls back the
+   * loop anyway, so even if GCC doesn't, keep the codebase simple and clearly
+   * convey the intent instead of trying to outsmart the compiler.
    */
-  for (T* end = aT + aNElem; aT < end; aT++) {
-    memset(aT, 0, sizeof(T));
-  }
+  memset(aT, 0, sizeof(T) * aNElem);
 }
 
 /** Set the contents of |aNElem| elements starting at |aT| to 0. */
@@ -151,7 +155,7 @@ template <typename T>
 static MOZ_ALWAYS_INLINE void PodMove(T* aDst, const T* aSrc, size_t aNElem) {
   static_assert(std::is_trivially_copyable_v<T>,
                 "PodMove requires trivially copyable types");
-  MOZ_ASSERT(aNElem <= SIZE_MAX / sizeof(T),
+  MOZ_ASSERT(aNElem <= std::numeric_limits<size_t>::max() / sizeof(T),
              "trying to move an impossible number of elements");
   memmove(aDst, aSrc, aNElem * sizeof(T));
 }