[PATCH] D103007: [LoopUtils] Avoid expanding complicated SCEVNAry when rewriteLoopExitValues

Mon May 24 05:42:48 PDT 2021

guopeilin added a comment.

In D103007#2776598 <https://reviews.llvm.org/D103007#2776598>, @lebedev.ri wrote:

> I'm not a fan of this direction.
> Which stack overflow are you seeing?

The details are that the variable `%add.i.2.i` can be computed by SCEV, and after expanding the SCEV value, this variable contains thousands of operands.
During ISel, we need to build a SelectionDAG first, so we need to visit all the operands to build SDNodes, and this will exhaust the stack due to plenty of operands.

Also, if you use `opt -indvars -S`, you can see that the program keeps printing the IR for a very long long time. More specifically, the program keeps printing the replaced variable.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D103007/new/

https://reviews.llvm.org/D103007