[llvm-dev] How to clean-up SCEVs from sext/zext/trunc ?

[Stefanos Baziotis via llvm-dev]

Hi everyone,

I've been using SCEV Delinearization but it fails when
other-than-pointer-size values are used in the subscripts. To make that
clear, say that we have a target in which pointers are 64-bit

for (int32_t i ...)
  for (int32_t j ...)
  a[i][j] = ...

doesn't work

while this:

for (int64_t i ...)
  for (int64_t j ...)

does work.

I assume that the former does not work because of sext expressions inside
the SCEV.
So, one idea is to clean SCEVs from those and emit run-time checks to
validate
that extending 32-bit to 64-bit is ok (if they're needed).

First of all, does that sound reasonable ? Do I miss something ?

Second, what is the best way to clean them ? One possible way is to rebuild
them (i.e.
traverse them and build new almost identical expressions, except that we
ignore the
problematic instructions). Though I haven't tried it yet.

Thanks,
Stefanos Baziotis
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