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aco: help clang 20 do some additions and subtractions

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clang 20 complains:

    ../src/amd/compiler/aco_assembler.cpp:837:28: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
      837 |       vaddr[num_vaddr + i] = reg(ctx, instr->operands.back(), 8) + i + 1;
          |       ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ../src/amd/compiler/aco_assembler.cpp:832:12: note: at offset 5 into destination object ‘vaddr’ of size 5
      832 |    uint8_t vaddr[5] = {0, 0, 0, 0, 0};
          |            ^~~~~
    ../src/amd/compiler/aco_assembler.cpp:837:28: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
      837 |       vaddr[num_vaddr + i] = reg(ctx, instr->operands.back(), 8) + i + 1;
          |       ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ../src/amd/compiler/aco_assembler.cpp:832:12: note: at offset 6 into destination object ‘vaddr’ of size 5
      832 |    uint8_t vaddr[5] = {0, 0, 0, 0, 0};
          |            ^~~~~
    ../src/amd/compiler/aco_assembler.cpp:837:28: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
      837 |       vaddr[num_vaddr + i] = reg(ctx, instr->operands.back(), 8) + i + 1;
          |       ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ../src/amd/compiler/aco_assembler.cpp:832:12: note: at offset 7 into destination object ‘vaddr’ of size 5
      832 |    uint8_t vaddr[5] = {0, 0, 0, 0, 0};
          |            ^~~~~

But `i < MIN2(instr->operands.back().size() - 1, 5 - num_vaddr)` means `i` is
at most `5 - num_vaddr - 1`, which means `vaddr[num_vaddr + i]` =>
`vaddr[num_vaddr + 5 - num_vaddr - 1]` => `vaddr[5 - 1]` => `vaddr[4]` which
is within the valid indices.

For some reason, using signed `int` instead allows clang to figure this
out, so let's do that since we don't need the extra range.

While at it, use ARRAY_SIZE(vaddr) instead of hard-coding the same `5`
in several places.

Backport-to: 25.0
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34625>
(cherry picked from commit 2bcb55f3f6)
This commit is contained in:
Eric Engestrom 2025-04-20 22:07:44 +02:00 • committed by Eric Engestrom
parent fec9695e67
commit cdd4f62e89
2 changed files with 3 additions and 3 deletions
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2
.pick_status.json
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@ -684,7 +684,7 @@
"description": "aco: help clang 20 do some additions and subtractions",
"nominated": true,
"nomination_type": 4,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": null,
"notes": null

4
src/amd/compiler/aco_assembler.cpp
View file

@ -832,8 +832,8 @@ emit_mimg_instruction_gfx12(asm_context& ctx, std::vector<uint32_t>& out, const
uint8_t vaddr[5] = {0, 0, 0, 0, 0};
for (unsigned i = 3; i < instr->operands.size(); i++)
vaddr[i - 3] = reg(ctx, instr->operands[i], 8);
unsigned num_vaddr = instr->operands.size() - 3;
for (unsigned i = 0; i < MIN2(instr->operands.back().size() - 1, 5 - num_vaddr); i++)
int num_vaddr = instr->operands.size() - 3;
for (int i = 0; i < (int)MIN2(instr->operands.back().size() - 1, ARRAY_SIZE(vaddr) - num_vaddr); i++)
vaddr[num_vaddr + i] = reg(ctx, instr->operands.back(), 8) + i + 1;
encoding = 0;