Bug 1550037 - patch 3 - Remove mAddr from the ShmBlock struct, as mShmem->memory() is now a trivial inline accessor. r=jwatt

In mozilla::ipc::SharedMemory, the memory() method was virtual, so we cached the address here
(although the compiler would likely have inlined the accessor as the `final` concrete subclass
was known). Anyhow, in base::SharedMemory it's a trivial (non-virtual) accessor, so there's
no sense in shadowing it here.

Differential Revision: https://phabricator.services.mozilla.com/D68789

--HG--
extra : moz-landing-system : lando

gfx/thebes/SharedFontList-impl.h

@@ -270,20 +270,19 @@ class FontList {
  private:
   struct ShmBlock {
     // Takes ownership of aShmem
-    ShmBlock(base::SharedMemory* aShmem, void* aAddr)
-        : mShmem(aShmem), mAddr(aAddr) {}
+    ShmBlock(base::SharedMemory* aShmem) : mShmem(aShmem) {}
+
+    // Get pointer to the mapped memory.
+    void* Memory() const { return mShmem->memory(); }
 
     // The first 32-bit word of each block holds the current amount allocated
     // in that block; this is updated whenever a new record is stored in the
     // block.
     std::atomic<uint32_t>& Allocated() const {
-      return *static_cast<std::atomic<uint32_t>*>(mAddr);
+      return *static_cast<std::atomic<uint32_t>*>(Memory());
     }
 
     mozilla::UniquePtr<base::SharedMemory> mShmem;
-    void* mAddr;  // Address where the shared memory block is mapped in this
-                  // process; avoids virtual call to mShmem->memory() each time
-                  // we need to convert between Pointer and a real C++ pointer.
   };
 
   Header& GetHeader() {

gfx/thebes/SharedFontList.cpp

@@ -60,7 +60,7 @@ void* Pointer::ToPtr(FontList* aFontList) const {
     }
     MOZ_ASSERT(block < aFontList->mBlocks.Length());
   }
-  return static_cast<char*>(aFontList->mBlocks[block]->mAddr) + Offset();
+  return static_cast<char*>(aFontList->mBlocks[block]->Memory()) + Offset();
 }
 
 void String::Assign(const nsACString& aString, FontList* aList) {
@@ -524,17 +524,11 @@ bool FontList::AppendShmBlock() {
     MOZ_CRASH("failed to create shared memory");
     return false;
   }
-  if (!newShm->Map(SHM_BLOCK_SIZE)) {
+  if (!newShm->Map(SHM_BLOCK_SIZE) || !newShm->memory()) {
     MOZ_CRASH("failed to map shared memory");
   }
 
-  char* addr = static_cast<char*>(newShm->memory());
-  if (!addr) {
-    MOZ_CRASH("null shared memory?");
-    return false;
-  }
-
-  ShmBlock* block = new ShmBlock(newShm, addr);
+  ShmBlock* block = new ShmBlock(newShm);
   // Allocate space for the Allocated() header field present in all blocks
   block->Allocated().store(4);
 
@@ -576,14 +570,10 @@ FontList::ShmBlock* FontList::GetBlockFromParent(uint32_t aIndex) {
   if (!newShm->SetHandle(handle, true)) {
     MOZ_CRASH("failed to set shm handle");
   }
-  if (!newShm->Map(SHM_BLOCK_SIZE)) {
+  if (!newShm->Map(SHM_BLOCK_SIZE) || !newShm->memory()) {
     MOZ_CRASH("failed to map shared memory");
   }
-  char* addr = static_cast<char*>(newShm->memory());
-  if (!addr) {
-    MOZ_CRASH("null shared memory?");
-  }
-  return new ShmBlock(newShm, addr);
+  return new ShmBlock(newShm);
 }
 
 bool FontList::UpdateShmBlocks() {
@@ -924,7 +914,7 @@ Pointer FontList::ToSharedPointer(const void* aPtr) {
   const char* p = (const char*)aPtr;
   const uint32_t blockCount = mBlocks.Length();
   for (uint32_t i = 0; i < blockCount; ++i) {
-    const char* blockAddr = (const char*)mBlocks[i]->mAddr;
+    const char* blockAddr = (const char*)mBlocks[i]->Memory();
     if (p >= blockAddr && p < blockAddr + SHM_BLOCK_SIZE) {
       return Pointer(i, p - blockAddr);
     }