InstructionCombining: merge realloc and free handling

[durin42]

Summary

As best I can tell, all this code _actually_ cares about is that it's a
function from an allocator family, not that it's specifically realloc or
free (which are the only options anyway). We can check for the allocator
family instead of looking at "is realloc like" and "is free like"
separately. The downside is that we need to add the free() codepath to
the work list, but since it returns nothing that should be
inconsequential in terms of cost.

[nikic]

I don't think this change is semantically right. For example, the function could now also be an allocator function that just happens to accept a pointer argument -- say, an allocator that allocates into a memory region. I think we do need to explicitly check that it's a free/realloc.

What's the motivation for this change?

[durin42]

In D123054#3472752, @nikic wrote:

I don't think this change is semantically right. For example, the function could now also be an allocator function that just happens to accept a pointer argument -- say, an allocator that allocates into a memory region. I think we do need to explicitly check that it's a free/realloc.

What's the motivation for this change?

Oh, great point. This was an unconsidered leftover from a previous incarnation of this (before allockind() existed) and it can be replaced by D124425 (which comes later in the sequence). I'll mark this as abandoned. Thanks!

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

for (User *U : PI->users()) {
           }
         }
 
         if (isRemovableWrite(*cast<CallBase>(I), PI, TLI)) {
           Users.emplace_back(I);
           continue;
         }
 
-        if (isFreeCall(I, &TLI) && getAllocationFamily(I, &TLI) == Family) {
-          assert(Family);
-          Users.emplace_back(I);
-          continue;
-        }
-
-        if (isReallocLikeFn(I, &TLI) &&
-            getAllocationFamily(I, &TLI) == Family) {
-          assert(Family);
+        if (Family && getAllocationFamily(I, &TLI) == Family) {
           Users.emplace_back(I);
           Worklist.push_back(I);
           continue;
         }
 
         return false;
 
       case Instruction::Store: {