Re: [PATCH] target/hppa: Move iaoq registers and thus reduce generated code size

[Richard Henderson <richard.henderson@linaro.org>]

On 7/30/23 09:30, Helge Deller wrote:
> On hppa the Instruction Address Offset Queue (IAOQ) registers specifies
> the next to-be-executed instructions addresses. Each generated TB writes those
> registers at least once, so those registers are used heavily in generated
> code.
> 
> Looking at the generated assembly, for a x86-64 host this code
> to write the address $0x7ffe826f into iaoq_f is generated:
> 0x7f73e8000184:  c7 85 d4 01 00 00 6f 82  movl     $0x7ffe826f, 0x1d4(%rbp)
> 0x7f73e800018c:  fe 7f
> 0x7f73e800018e:  c7 85 d8 01 00 00 73 82  movl     $0x7ffe8273, 0x1d8(%rbp)
> 0x7f73e8000196:  fe 7f
> 
> With the trivial change, by moving the variables iaoq_f and iaoq_b to
> the top of struct CPUArchState, the offset to %rbp is reduced (from
> 0x1d4 to 0), which allows the x86-64 tcg to generate 3 bytes less of
> generated code per move instruction:
> 0x7fc1e800018c:  c7 45 00 6f 82 fe 7f     movl     $0x7ffe826f, (%rbp)
> 0x7fc1e8000193:  c7 45 04 73 82 fe 7f     movl     $0x7ffe8273, 4(%rbp)
> 
> Overall this is a reduction of generated code (not a reduction of
> number of instructions).
> A test run with checks the generated code size by running "/bin/ls"
> with qemu-user shows that the code size shrinks from 1616767 to 1569273
> bytes, which is ~97% of the former size.
> 
> Signed-off-by: Helge Deller<deller@gmx.de>

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~