[PATCH] D32674: [LoopIdiom] PR32811 check for safety while expanding
Eli Friedman via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon May 1 14:11:53 PDT 2017
efriedma added inline comments.
================
Comment at: lib/Transforms/Scalar/LoopIdiomRecognize.cpp:823
Value *NumBytes =
Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
----------------
hiraditya wrote:
> efriedma wrote:
> > Do we also need to check whether it's safe to expand NumBytesS?
> I don't think so (IIUC), because the NumBytes is based on the trip count of the loop*storesize, both of them should be safe to expand if the loop has a valid SCEV.
The store size is a constant, so that's obviously fine, but I don't see how the loop's trip count is obviously safe to expand; . Consider, e.g.:
```
#include <stdio.h>
void f(unsigned a, unsigned b, char* x) {
for (int j = 0; j < a; j++)
if (b != 0)
for (long long i = 0; i < a / b; ++i)
x[i] = 0;
}
```
https://reviews.llvm.org/D32674
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