About cctest/test-run-load-store/RunLoadStoreZeroExtend64 in v8

[Yahan Lu]

Hi all ~

   I notice the case cctest/test-run-load-store/RunLoadStoreZeroExtend64.  

   It  load a uint32 from a pointer and store it back by Kword64

    Node* load64 = m.LoadFromPointer(&buffer[0], MachineType::Uint64());

    m.StoreToPointer(&buffer[3], MachineRepresentation::kWord64, load32);

    Does V8 default uint32 must be unsigned extended to 64bit in 64-bit platform?

    Due to riscv64 spec, riscv64 load a uint32 into register  and SignExtend to 64bit.

https://github.com/riscv-collab/riscv-gnu-toolchain/issues/680#issuecomment-666367253

https://github.com/riscv-collab/riscv-gnu-toolchain/issues/680#issuecomment-686225804

 

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aswaterman commented on 3 Sep 2020

The sign-extension is an ABI constraint. If you want zero extension, you need to use a wider unsigned type, like uint64_t.

sorear commented on 30 Jul 2020

The intent of the RISC-V ISA is that 32-bit C values are stored sign extended in registers, even for unsigned types.

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