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A bit more analysis of a memset-related README entry.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128107 91177308-0d34-0410-b5e6-96231b3b80d8
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Eli Friedman 2011-03-22 20:49:53 +00:00
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lib/Target/README.txt
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@ -2074,11 +2074,12 @@ for.end: ; preds = %entry
}
This shouldn't need the ((zext (%n - 1)) + 1) game, and it should ideally fold
the two memset's together. The issue with %n seems to stem from poor handling
of the original loop.
the two memset's together.
To simplify this, we need SCEV to know that "n != 0" because of the dominating
conditional. That would turn the second memset into a simple memset of 'n'.
The issue with the addition only occurs in 64-bit mode, and appears to be at
least partially caused by Scalar Evolution not keeping its cache updated: it
returns the "wrong" result immediately after indvars runs, but figures out the
expected result if it is run from scratch on IR resulting from running indvars.
//===---------------------------------------------------------------------===//