[all-commits] [llvm/llvm-project] b0c2dc: [flang][PFT-to-MLIR] allocate missing body blocks ...

[Kareem Ergawy via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b0c2dc0cf8f8de2fd2f0306deea0c5fcd07282da
      https://github.com/llvm/llvm-project/commit/b0c2dc0cf8f8de2fd2f0306deea0c5fcd07282da
  Author: Kareem Ergawy <kergawy at nvidia.com>
  Date:   2026-07-22 (Wed, 22 Jul 2026)

  Changed paths:
    M flang/include/flang/Lower/DirectivesCommon.h
    A flang/test/Lower/OpenMP/wsloop-computed-goto.f90
    A flang/test/Lower/OpenMP/wsloop-select-case.f90

  Log Message:
  -----------
  [flang][PFT-to-MLIR] allocate missing body blocks in `createEmptyRegionBlocks` (#210950)

Problem
-------
Under -mmlir --wrap-unstructured-constructs-in-execute-region, branch
lowering hit a null Evaluation::block for body statements inside an
OpenMP loop. genMultiwayBranch tripped

Bridge.cpp: Assertion `block && "missing multiway branch block"' failed

and genFIR(SelectCaseStmt) tripped

    Bridge.cpp: Assertion `e->block && "missing CaseStmt block"' failed

The wrap machinery decides an unstructured DO/IF is wrappable and stops
propagating its isUnstructured flag to the enclosing OpenMPConstruct.
The OMP construct's isUnstructured stays false, so the top-level
createEmptyBlocks treats it as a structured directive with nested
evaluations — it allocates only the OMP construct's first-nested block
and does not recurse into the DO body. Then OMP loop lowering takes
over the body via createEmptyRegionBlocks, which was written to
*re-parent* pre-existing blocks into its region and silently skipped
evals whose .block was still null. Body targets (e.g. label 17's
ContinueStmt, or a SelectCase's CaseStmts) therefore had no block when
the consumer read evalOfLabel(...).block, tripping the asserts.

Solution
--------
Restore the invariant that consumers of eval.block can trust it at
lowering time. In createEmptyRegionBlocks (DirectivesCommon.h), when an
eval has isNewBlock but no .block, create one in the current region
alongside the existing re-parenting path. The OMP lowering path then
finds pre-allocated blocks for the whole body — matching the state that
existed before the wrap feature changed isUnstructured propagation —
without any lazy-allocation logic at consumer sites.

Co-authored-by: Claude Opus 4.7 <noreply at anthropic.com>



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