Juneyoung Lee 1605593440 [SimplifyLibCalls] Fix memchr opt to use CreateLogicalAnd ...

This fixes a bug at LibCallSimplifier::optimizeMemChr which does the following transformation:

```
// memchr("\r\n", C, 2) != nullptr -> (1 << C & ((1 << '\r') | (1 << '\n')))
// != 0
//   after bounds check.
```

As written above, a bounds check on C (whether it is less than integer bitwidth) is done before doing `1 << C` otherwise 1 << C will overflow.
If the bounds check is false, the result of (1 << C & ...) must not be used at all, otherwise the result of shift (which is poison) will contaminate the whole results.
A correct way to encode this is `select i1 (bounds check), (1 << C & ...), false`  because select does not allow the unused operand to contaminate the result.
However, this optimization was introducing `and (bounds check), (1 << C & ...)` which cannot do that.

The bug was found from compilation of this C++ code: https://reviews.llvm.org/rG2fd3037ac615#1007197

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D104901

2021-06-26 05:59:35 +09:00

126 KiB

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