[mips][wasm] Correct wasm address space limit.

MIPS64 has a user space of 2^40 bytes on most processors, address
space limits needs to be smaller. 256G is ok, but it will cause
many wasm tests get a OOM error.

This patch also skip some tests which need correct IEEE-745 2008
NaN bit patterns on mips.

Change-Id: I52968df3934e8748b2c42a0abf19db1540441d2b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1712929Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Yu Yin <xwafish@gmail.com>
Cr-Commit-Position: refs/heads/master@{#63050}

src/objects/backing-store.cc

@@ -28,7 +28,7 @@ constexpr bool kUseGuardRegions = false;
 #if V8_TARGET_ARCH_MIPS64
 // MIPS64 has a user space of 2^40 bytes on most processors,
 // address space limits needs to be smaller.
-constexpr size_t kAddressSpaceLimit = 0x4000000000L;  // 256 GiB
+constexpr size_t kAddressSpaceLimit = 0x8000000000L;  // 512 GiB
 #elif V8_TARGET_ARCH_64_BIT
 constexpr size_t kAddressSpaceLimit = 0x10100000000L;  // 1 TiB + 4 GiB
 #else

test/wasm-spec-tests/wasm-spec-tests.status

@@ -22,6 +22,8 @@
   'tests/f64': [SKIP],
   'tests/f32_bitwise': [SKIP],
   'tests/f64_bitwise': [SKIP],
+  'tests/proposals/reference-types/conversions':  [SKIP],
+  'tests/proposals/bulk-memory-operations/conversions': [SKIP],
 }],  # 'arch == mipsel or arch == mips64el or arch == mips or arch == mips64'
 
 ['(arch == mipsel or arch == mips64el or arch == mips or arch == mips64) and not simulator_run', {