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Nested loops do not restore aL register with nested loops #86

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Wunkolo opened this issue Apr 22, 2024 · 0 comments
Open

Nested loops do not restore aL register with nested loops #86

Wunkolo opened this issue Apr 22, 2024 · 0 comments

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@Wunkolo
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Wunkolo commented Apr 22, 2024

Issue

Issue revealed in the shader unit-tests in #72, the shader-interpreter does not correctly handle nested loops properly. Specifically the aL(loop counter) register is not properly incremented and restored for the parent-loop.

1: -------------------------------------------------------------------------------
1: Nested Loop - ShaderInterpreterTest
1: -------------------------------------------------------------------------------
1: /__w/citra/citra/src/tests/video_core/shader/shader_jit_compiler.cpp:636
1: ...............................................................................
1: 
1: /__w/citra/citra/src/tests/video_core/shader/shader_jit_compiler.cpp:669: FAILED:
1:   REQUIRE( shader_unit.address_registers[2] == expected_aL )
1: with expansion:
1:   0 == 5

The top-most loop can end or break but multiple loops may need to be iterated at the same program counter, this is currently not handled.

citra/src/video_core/shader/shader_interpreter.cpp

Lines 709 to 722 in e26ceab

if (!loop_stack.empty() &&
(loop_stack.back().end_address == old_program_counter 1 || is_break)) {
auto& loop = loop_stack.back();
state.address_registers[2] = loop.address_increment;
if (!is_break && loop.loop_downcounter--) {
program_counter = loop.entry_address;
} else {
program_counter = loop.end_address;
// Only restore previous value if there is a surrounding LOOP scope.
if (loop_stack.size() > 1)
state.address_registers[2] = loop.previous_aL;
loop_stack.pop_back();
}
}

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@Wunkolo