TailRecursionElimination does not cleanup a stale basicblock

[Arnaud A. de Grandmaison]

When the BasicBlock containing the return instrution has a PHI with 2

incoming values, FoldReturnIntoUncondBranch will remove the no longer

used incoming value and remove the no longer needed phi as well. This

leaves us with a BB that no longer has a PHI, but the subsequent call

to FoldReturnIntoUncondBranch from FoldReturnAndProcessPred will not

remove the return instruction (which still uses the result of the call

instruction). This prevents EliminateRecursiveTailCall to remove

the value, as it is still being used in a basicblock which has no

predecessors.

 

The basicblock can not be erased on the spot, because its iterator is

still being used in runTRE.

 

This issue was exposed when removing the threshold on size for lifetime

marker insertion for named temporaries in clang. The testcase is a much

reduced version of peelOffOuterExpr(const Expr*, const ExplodedNode *)

from clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp.

 

Cheers,

--

Arnaud A. de Grandmaison

 
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