[TIR][FEAT] Require DeclBuffer before use in verify_well_formed

[tqchen]

Summary

• Add UndefinedBufferVerifier to verify_well_formed that checks buffer-scope invariants: buffers declared via buffer_map, DeclBuffer, alloc_buffers, match_buffers, or buffer_bind_scope must not be used outside their declaration scope
• In schedule-level TIR (functions with SBlock nodes), all buffers in BufferLoad/BufferStore must have a prior declaration
• Fix TIRVisitorWithPath to call WithDef for Buffer at two previously missing sites: SBlock::match_buffers and AttrStmt::buffer_bind_scope

Follows up on the concept from draft PR #14778 (RFC#70). The check is gated to schedule-level TIR only, since FlattenBuffer strips DeclBuffer statements.

Test plan

• 6 new tests in test_tir_analysis_verify_well_formed.py (buffer_map, decl_buffer, alloc_buffer, match_buffer, error_out_of_scope, error_undeclared)
• All 23 existing + new tests pass
• CI checks

[gemini-code-assist]

Summary of Changes

Hello, 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 significantly enhances the TensoIR (TIR) verification process by introducing robust checks for buffer declaration and usage. It ensures that buffers are always used within their defined scopes and, for schedule-level TIR, that all buffers are explicitly declared before use. This improves the correctness and reliability of TIR programs by catching common buffer-related errors early in the compilation pipeline.

Highlights

• New Buffer Verification: Introduced UndefinedBufferVerifier to enforce buffer-scope invariants within verify_well_formed, ensuring buffers are used only within their declared scopes.
• Stricter Schedule-Level TIR Checks: Implemented a stricter check for schedule-level TIR, requiring all buffers used in BufferLoad or BufferStore to have a prior declaration.
• TIRVisitorWithPath Fixes: Corrected TIRVisitorWithPath to properly track Buffer definitions in SBlock::match_buffers and AttrStmt::buffer_bind_scope.

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Changelog

• src/tir/analysis/verify_well_formed.cc
  • Added UndefinedBufferVerifier class to check buffer declaration scopes and usage.
  • Integrated UndefinedBufferVerifier into VerifyWellFormed for both PrimFunc and IRModule verification.
• src/tir/ir/tir_visitor_with_path.cc
  • Updated AttrStmtNode visitor to include DefContext<Buffer> for buffer_bind_scope attributes.
  • Updated SBlockNode visitor to include DefContext<Buffer> for match_buffers.
• tests/python/tir-analysis/test_tir_analysis_verify_well_formed.py
  • Added test_buffer_in_buffer_map_is_well_formed to verify buffers from function parameters.
  • Added test_decl_buffer_is_well_formed to verify buffers declared via DeclBuffer.
  • Added test_alloc_buffer_in_block_is_well_formed to verify buffers allocated in SBlock::alloc_buffers.
  • Added test_match_buffer_in_block_is_well_formed to verify buffers matched in SBlock::match_buffers.
  • Added test_error_buffer_used_out_of_decl_scope to test out-of-scope buffer usage.
  • Added test_error_undeclared_buffer_in_schedulable_tir to test undeclared buffer usage in schedule-level TIR.

Activity

• No human activity (comments, reviews, progress updates) was provided in the context.

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[gemini-code-assist]

Code Review

This pull request introduces a new UndefinedBufferVerifier to enforce buffer declaration and scope rules in TIR, which is a valuable addition for ensuring TIR well-formedness. The changes correctly identify out-of-scope and undeclared buffer usages, particularly for schedule-level TIR. The fixes in TIRVisitorWithPath to properly handle buffer definitions from match_buffers and buffer_bind_scope are also correct and necessary. The overall implementation is solid and well-tested. I've found one issue in the logic for tracking out-of-scope buffers that could lead to misleading error messages, for which I've provided a suggestion.

[gemini-code-assist]

std::unordered_map::insert does not update the value if an element with the same key already exists. If a buffer is defined, goes out of scope, and is then redefined in a later non-overlapping scope, previously_defined_ will retain the AccessPath from the end of the first scope. This can lead to confusing error messages that point to an older, incorrect declaration site. Using operator[] or insert_or_assign will ensure the path to the most recent out-of-scope definition is always stored.

Suggested change

	previously_defined_.insert({buffer, path});
	previously_defined_[buffer] = path;