[SPIRV] Fix forloop codegen in vulkan

[tqchen]

This PR fixes a regression in vulkan codegen where we need to create phi node after the start label.

[tqchen]

cc @wrongtest-intellif

[gemini-code-assist]

Summary of Changes

Hello @tqchen, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a regression in the Vulkan code generation for SPIRV by correcting the placement of Phi nodes within for loops. The change ensures that the Phi node, essential for loop variable management, is created after the loop's start label, which is a requirement for proper Vulkan codegen. This fix improves the stability and correctness of generated SPIRV code for loops.

Highlights

• SPIRV Code Generation Fix: The creation of the spirv::PhiValue for loop variables has been relocated to occur after the StartLabel call within the loop head. This addresses a regression in Vulkan codegen where Phi nodes were incorrectly placed.
• Loop Step Type Inference: The type inference for the loop step calculation now correctly uses init_value.stype instead of loop_var.stype, aligning with the new placement of loop_var's definition and ensuring correct type handling.

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Changelog

• src/target/spirv/codegen_spirv.cc
  • Moved the declaration and initialization of spirv::PhiValue loop_var from before the loop head's StartLabel call to immediately after it, within the loop head block.
  • Adjusted the type argument for builder_->IntImm and builder_->UIntImm in the loop step calculation from loop_var.stype to init_value.stype to reflect the new order of loop_var definition.

Activity

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[gemini-code-assist]

Code Review

This pull request addresses a regression in SPIR-V code generation for Vulkan loops. The core issue was that the OpPhi instruction for the loop variable was generated before the loop header's OpLabel, which is invalid according to the SPIR-V specification. The fix correctly relocates the OpPhi instruction creation to after the OpLabel, ensuring the generated shader is valid. The changes are logical, correct, and well-contained. I have no further suggestions.

[MasterJH5574]

Thanks for the fix!