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

[Jeff Law]

On 4/17/25 11:50 AM, Andrew Pinski wrote:

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.

OK
jeff