[mips64][compiler] Fix kAtomicLoadWord32

Allows atomic loading of an unsigned 32bit value from 64bit widths.

Bug: v8:12093
Change-Id: Ib6ca2f3f44d4e82e5e41bf1ca0494e48ca90a21a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3096888Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Auto-Submit: Liu yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#76307}

src/compiler/backend/mips64/code-generator-mips64.cc

@@ -1883,7 +1883,10 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       ASSEMBLE_ATOMIC_LOAD_INTEGER(Lhu);
       break;
     case kAtomicLoadWord32:
-      ASSEMBLE_ATOMIC_LOAD_INTEGER(Lw);
+      if (AtomicWidthField::decode(opcode) == AtomicWidth::kWord32)
+        ASSEMBLE_ATOMIC_LOAD_INTEGER(Lw);
+      else
+        ASSEMBLE_ATOMIC_LOAD_INTEGER(Lwu);
       break;
     case kMips64Word64AtomicLoadUint64:
       ASSEMBLE_ATOMIC_LOAD_INTEGER(Ld);