Re: [PATCH v2] testsuite: arm: Check that a far jump is used in thumb1-far-jump-2.c

[Torbjorn SVENSSON]

On 2024-12-04 12:41, Richard Earnshaw (lists) wrote:

On 22/11/2024 09:37, Torbjörn SVENSSON wrote:

Changes since v1:

- Rewrote the padding instructions in the macro to instead write to volatile
   memory. This ensures that every expansion of the base macro is exactly 2
   bytes.

If the `GO()` in f3 is removed, the generated assembly would be reduced to:

f3:
         @ args = 0, pretend = 0, frame = 0
         @ frame_needed = 0, uses_anonymous_args = 0
         push    {lr}
         cmp     r0, #0
         bne     .LCB7
         bl      .L1     @far jump
.LCB7:
         movs    r2, #1
         ldr     r3, .L6
         str     r2, [r3]
         ...
         str     r2, [r3]
.L1:
         @ sp needed
         pop     {pc}

Would this assembly be as stable as with the `GO()` in f3? If so, would it be
preferred to generate the simpler assembly in the test?

Ok for trunk as it is or perhaps with the simpler assembly?

--

With the changes in r15-1579-g792f97b44ff, the code used as "padding" in
the test case is optimized way. Prevent this optimization by forcing a
read of the volatile memory.
Also, validate that there is a far jump in the generated assembler.

Without this patch, the generated assembler is reduced to:
f3:
         cmp     r0, #0
         beq     .L1
         ldr     r4, .L6
.L1:
         bx      lr
.L7:
         .align  2
.L6:
         .word   g_0_1

With the patch, the generated assembler is:
f3:
         movs    r2, #1
         ldr     r3, .L6
         push    {lr}
         str     r2, [r3]
         cmp     r0, #0
         bne     .LCB10
         bl      .L1     @far jump
.LCB10:
         b       .L7
.L8:
         .align  2
.L6:
         .word   .LANCHOR0
.L7:
         str     r2, [r3]
         ...
         str     r2, [r3]
.L1:
         pop     {pc}

gcc/testsuite/ChangeLog:

        * gcc.target/arm/thumb1-far-jump-2.c: Write to volatile memmory
        in macro to avoid optimization.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svens...@foss.st.com>
---
  .../gcc.target/arm/thumb1-far-jump-2.c        | 95 ++++++++++---------
  1 file changed, 51 insertions(+), 44 deletions(-)

OK.

R.

Pushed as r15-6166-gb7e11b49992.

Kind regards,
Torbjörn