[PATCH] D102259: [flang] Limit the depth of expressions that the compiler will handle

[Pete Steinfeld via Phabricator via llvm-commits]

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The compiler analyzes expressions recusively.  Large expressions consume large
amounts of stack space.  Very large expressions can cause the compiler to
overflow the stack, which results in a seg fault.

I fixed this by imposing a limit of 1000 for the depth of the expression tree
analyzed by the compiler.  Upon reaching this limit, the compiler will emit a
message, unwind from the analysis of that expression, and proceed with the rest
of the compilation.

The limit of 1000 is a little arbitrary.  I experimentally verified that the
compiler cannot handle a limit of 5000, and 1000 seems big enough.

I added a test that will produce a seg fault without this change.  It also
contains an expression with 1000 operations that gets constant folded.  This
demonstrates that, if we can analyze an expression, we can fold it.  I also
included two cases where we create array constructors of many more elements
than the expression limit to verify that we can handle large array
constructors.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102259

Files:
  flang/include/flang/Semantics/expression.h
  flang/lib/Semantics/expression.cpp
  flang/test/Semantics/big-expr.f90

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