[mips64] Fix implicit conversion loses integer precision warning

Change-Id: Ic2bbf2b3ff542d916da43929445bd83553b5091f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2401952Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#69796}

src/codegen/mips64/macro-assembler-mips64.cc

@@ -4378,13 +4378,13 @@ void TurboAssembler::BranchLong(Label* L, BranchDelaySlot bdslot) {
   } else {
     // Generate position independent long branch.
     BlockTrampolinePoolScope block_trampoline_pool(this);
-    int64_t imm64;
-    imm64 = branch_long_offset(L);
+    int64_t imm64 = branch_long_offset(L);
     DCHECK(is_int32(imm64));
+    int32_t imm32 = static_cast<int32_t>(imm64);
     or_(t8, ra, zero_reg);
     nal();                                        // Read PC into ra register.
-    lui(t9, (imm64 & kHiMaskOf32) >> kLuiShift);  // Branch delay slot.
-    ori(t9, t9, (imm64 & kImm16Mask));
+    lui(t9, (imm32 & kHiMaskOf32) >> kLuiShift);  // Branch delay slot.
+    ori(t9, t9, (imm32 & kImm16Mask));
     daddu(t9, ra, t9);
     if (bdslot == USE_DELAY_SLOT) {
       or_(ra, t8, zero_reg);
@@ -4402,12 +4402,12 @@ void TurboAssembler::BranchAndLinkLong(Label* L, BranchDelaySlot bdslot) {
   } else {
     // Generate position independent long branch and link.
     BlockTrampolinePoolScope block_trampoline_pool(this);
-    int64_t imm64;
-    imm64 = branch_long_offset(L);
+    int64_t imm64 = branch_long_offset(L);
     DCHECK(is_int32(imm64));
-    lui(t8, (imm64 & kHiMaskOf32) >> kLuiShift);
+    int32_t imm32 = static_cast<int32_t>(imm64);
+    lui(t8, (imm32 & kHiMaskOf32) >> kLuiShift);
     nal();                              // Read PC into ra register.
-    ori(t8, t8, (imm64 & kImm16Mask));  // Branch delay slot.
+    ori(t8, t8, (imm32 & kImm16Mask));  // Branch delay slot.
     daddu(t8, ra, t8);
     jalr(t8);
     // Emit a nop in the branch delay slot if required.