diff mbox series

target/hppa: Move iaoq registers and thus reduce generated code size

Message ID ZMaQGwK1Ikj27ZPk@p100
State New
Headers show
Series target/hppa: Move iaoq registers and thus reduce generated code size | expand

Commit Message

Helge Deller July 30, 2023, 4:30 p.m. UTC 
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>

Comments

Richard Henderson July 30, 2023, 5:50 p.m. UTC | #1 
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~
Philippe Mathieu-Daudé July 31, 2023, 9:55 a.m. UTC | #2 
On 30/7/23 18:30, 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: Philippe Mathieu-Daudé <philmd@linaro.org>
diff mbox series

Patch

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;