gimple-fold: Improve optimize_memcpy_to_memset by walking back until aliasing says the ref is a may clobber. [PR118947]

The case here is we have:
```
    char buf[32] = {};
    void* ret = aaa();
    __builtin_memcpy(ret, buf, 32);
```

And buf does not escape.  But we don't prop the zeroing from buf to the memcpy statement
because optimize_memcpy_to_memset only looks back one statement. This can be fixed to look back
until we get an statement that may clobber the reference.  If we get a phi node, then we don't do
anything.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/118947

gcc/ChangeLog:

	* gimple-fold.cc (optimize_memcpy_to_memset): Walk back until we get a
	statement that may clobber the read.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr118947-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

0 files changed, 0 insertions, 0 deletions