RFR: 8282204: Use lea instructions for arithmetic operations on x86_64 [v9]

[Quan Anh Mai]

On Fri, 4 Mar 2022 08:23:21 GMT, Jie Fu <jiefu at openjdk.org> wrote:

> Shall we also remove `leaP_rReg_imm` ?

Done.

> Did you check cases like 32-bit calculation overflow?
> Maybe add a jtreg test to verify the results?

According to Intel manual, volume 1, section 3.3.7:

> All 16-bit and 32-bit address calculations are zero-extended in IA-32e mode to form 64-bit addresses. Address calculations are first truncated to the effective address size of the current mode (64-bit mode or compatibility mode), as overridden by any address-size prefix. The result is then zero-extended to the full 64-bit address width.

It is trivial that truncation to 32 bit and zero extension from 32 bit keep the lower 32 bits untouched. Also, the lower 32 bits of integral additions and multiplications only depends on the lower 32 bits of the operands. As a result, calculations with 32-bit address, 32-bit operand give the same result as those with 64-bit address, 32-bit operand since the lower 32 bits are similar and the upper 32 bits are all zero. Also, looking at the generated code for (using `unsigned int` because overflow cause wrapping, similar to Java calculations)

    unsigned int test(unsigned int x, unsigned int y) {
        return x + y * 4 + 100;
    }

GCC conveniently output [`leal    0x64(%rdi,%rsi,4), %eax`](https://godbolt.org/z/M6o7zjoe3) with 64-bit address (without 0x67 prefix). So, we can be confident that we don't make a mistake here.

Thanks a lot.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7560