Fixes issue #43205: ICE in Rvalue::Len evaluation. #44060
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- fixes evaluation of array length for zero-sized type referenced by rvalue operand. - adds test to verify fix. Cause of the issue. Zero-sized aggregates are handled as operands, not lvalues. Therefore while visiting Assign statement by LocalAnalyser, mark_as_lvalue() is not called for related Local. This behaviour is controlled by rvalue_creates_operand() method. As result it causes error later, when rvalue operand is evaluated in trans_rvalue_operand() while handling Rvalue::Len case. Array length evaluation invokes trans_lvalue() which expects referenced Local to be value, not operand. How it is fixed. In certain cases result of Rvalue::Len can be evaluated without calling trans_lvalue(). Method evaluate_array_len() is introduced to handle length evaluation for zero-sized types referenced by Locals.
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Fixes issue #43205: ICE in Rvalue::Len evaluation. - fixes evaluation of array length for zero-sized type referenced by rvalue operand. - adds test to verify fix. *Cause of the issue*. Zero-sized aggregates are handled as operands, not lvalues. Therefore while visiting `Assign` statement by `LocalAnalyser`, `mark_as_lvalue()` is not called for related `Local`. This behaviour is controlled by `rvalue_creates_operand()` method. As result it causes error later, when rvalue operand is evaluated in `trans_rvalue_operand()` while handling `Rvalue::Len` case. Array length evaluation invokes `trans_lvalue()` which expects referenced `Local` to be value, not operand. *How it is fixed*. In certain cases result of `Rvalue::Len` can be evaluated without calling `trans_lvalue()`. Method `evaluate_array_len()` is introduced to handle length evaluation for zero-sized types referenced by Locals. *Some concerns*. - `trans_lvalue()` has two other entry points in `rvalue.rs`: it is invoked while handling `Rvalue::Ref` and `Rvalue::Discriminant`. There is a chance those may produce the same issue, but I've failed to write a specific test that leads to this. - `evaluate_array_len()` performs the same check (matches lvalue and `Local`), which is performed again in `trans_lvalue()`. Without changing `trans_lvalue()` signature to make it aware that caller deals with rvalue, it seems there is no cheap solution to avoid this check.
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☀️ Test successful - status-appveyor, status-travis |
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Cause of the issue.
Zero-sized aggregates are handled as operands, not lvalues. Therefore while visiting
Assignstatement byLocalAnalyser,mark_as_lvalue()is not called for relatedLocal. This behaviour is controlled byrvalue_creates_operand()method.As result it causes error later, when rvalue operand is evaluated in
trans_rvalue_operand()while handlingRvalue::Lencase. Array length evaluation invokestrans_lvalue()which expects referencedLocalto be value, not operand.How it is fixed.
In certain cases result of
Rvalue::Lencan be evaluated without callingtrans_lvalue(). Methodevaluate_array_len()is introduced to handle lengthevaluation for zero-sized types referenced by Locals.
Some concerns.
trans_lvalue()has two other entry points inrvalue.rs: it is invoked while handlingRvalue::RefandRvalue::Discriminant. There is a chance those may produce the same issue, but I've failed to write a specific test that leads to this.evaluate_array_len()performs the same check (matches lvalue andLocal), which is performed again intrans_lvalue(). Without changingtrans_lvalue()signature to make it aware that caller deals with rvalue, it seems there is no cheap solution to avoid this check.