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. Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org> Reviewed-by: Richard Henderson <richard.hender...@linaro.org> Signed-off-by: Helge Deller <del...@gmx.de> Cc: qemu-sta...@nongnu.org --- target/hppa/cpu.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/target/hppa/cpu.h b/target/hppa/cpu.h index 9fe79b1242..75c5c0ccf7 100644 --- a/target/hppa/cpu.h +++ b/target/hppa/cpu.h @@ -168,6 +168,9 @@ typedef struct { } hppa_tlb_entry; typedef struct CPUArchState { + target_ureg iaoq_f; /* front */ + target_ureg iaoq_b; /* back, aka next instruction */ + target_ureg gr[32]; uint64_t fr[32]; uint64_t sr[8]; /* stored shifted into place for gva */ @@ -186,8 +189,6 @@ typedef struct CPUArchState { target_ureg psw_cb; /* in least significant bit of next nibble */ target_ureg psw_cb_msb; /* boolean */ - target_ureg iaoq_f; /* front */ - target_ureg iaoq_b; /* back, aka next instruction */ uint64_t iasq_f; uint64_t iasq_b; -- 2.41.0