Bug 1615434 - Increase maximum initial memory size to 2GiB. r=lth

The spec no longer has an initial memory size limit, so we should allow up to
the limit imposed upon us by ArrayBuffer.

Differential Revision: https://phabricator.services.mozilla.com/D80140

js/src/wasm/WasmConstants.h

@@ -840,6 +840,11 @@ enum class NameType { Module = 0, Function = 1, Local = 2 };
 
 enum class FieldFlags { Mutable = 0x01, AllowedMask = 0x01 };
 
+// The WebAssembly spec hard-codes the virtual page size to be 64KiB and
+// requires the size of linear memory to always be a multiple of 64KiB.
+
+static const unsigned PageSize = 64 * 1024;
+
 // These limits are agreed upon with other engines for consistency.
 
 static const unsigned MaxTypes = 1000000;
@@ -861,7 +866,7 @@ static const unsigned MaxParams = 1000;
 static const unsigned MaxResults = 1000;
 static const unsigned MaxStructFields = 1000;
 static const unsigned MaxMemoryLimitField = 65536;
-static const unsigned MaxMemoryPages = 16384;
+static const unsigned MaxMemoryPages = INT32_MAX / PageSize;
 static const unsigned MaxStringBytes = 100000;
 static const unsigned MaxModuleBytes = 1024 * 1024 * 1024;
 static const unsigned MaxFunctionBytes = 7654321;

js/src/wasm/WasmTypes.cpp

@@ -45,6 +45,10 @@ using mozilla::MakeEnumeratedRange;
 #  endif
 #endif
 
+static_assert(MaxMemoryPages ==
+                  ArrayBufferObject::MaxBufferByteLength / PageSize,
+              "invariant");
+
 // All plausible targets must be able to do at least IEEE754 double
 // loads/stores, hence the lower limit of 8.  Some Intel processors support
 // AVX-512 loads/stores, hence the upper limit of 64.

js/src/wasm/WasmTypes.h

@@ -3098,11 +3098,6 @@ extern bool IsValidARMImmediate(uint32_t i);
 
 extern uint64_t RoundUpToNextValidARMImmediate(uint64_t i);
 
-// The WebAssembly spec hard-codes the virtual page size to be 64KiB and
-// requires the size of linear memory to always be a multiple of 64KiB.
-
-static const unsigned PageSize = 64 * 1024;
-
 // Bounds checks always compare the base of the memory access with the bounds
 // check limit. If the memory access is unaligned, this means that, even if the
 // bounds check succeeds, a few bytes of the access can extend past the end of