| commit | c7c5666aac543a49b485a133f4a94865e2613a43 | [log] [tgz] |
|---|---|---|
| author | jeanPerier <jperier@nvidia.com> | Tue May 14 13:34:46 2024 +0200 |
| committer | GitHub <noreply@github.com> | Tue May 14 13:34:46 2024 +0200 |
| tree | e826a5a588d3b91827abdd39559ee20ba9767b83 | |
| parent | e6d3a4212d20b49a8e63f11fedea79cccf261479 [diff] |
[flang] Do not hoist all scalar sub-expressions from WHERE constructs (#91395) The HLFIR pass lowering WHERE (hlfir.where op) was too aggressive in its hoisting of scalar sub-expressions from LHS/RHS/MASKS outside of the loops generated for the WHERE construct. This violated F'2023 10.2.3.2 point 10 that stipulated that elemental operations must be evaluated only for elements corresponding to true values, because scalar operations are still elemental, and hoisting them is invalid if they could have side effects (e.g, division by zero) and if the MASK is always false (i.e., the loop body is never evaluated). The difficulty is that 10.2.3.2 point 9 mandates that nonelemental function must be evaluated before the loops. So it is not possible to simply stop hoisting non hlfir.elemental operations. Marking calls with an elemental/nonelemental attribute would not allow the pass to be correct if inlining is run before and drops this information, beside, extracting the argument tree that may have been CSE-ed with the rest of the expression evaluation would be a bit combursome. Instead, lower nonelemental calls into a new hlfir.exactly_once operation that will allow retaining the information that the operations contained inside its region must be hoisted. This allows inlining to operate before if desired in order to improve alias analysis. The LowerHLFIROrderedAssignments pass is updated to only hoist the operations contained inside hlfir.exactly_once bodies.
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