[PATCH] D99121: [IR][InstCombine] IntToPtr Produces Typeless Pointer To Byte

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri added subscribers: t.p.northover, dblaikie.
lebedev.ri added a comment.

In D99121#2644223 <https://reviews.llvm.org/D99121#2644223>, @nlopes wrote:

> The pointee type in LLVM doesn't really matter. It's even supposed to disappear one day after the migration is completed.
> E.g., i8* and i64* are exactly the same thing: they are pointers to data.

Yep. That will be indeed a great to see.

> So, I don't understand the motivation for this patch. It doesn't solve the root cause of the problem (which one btw?).

It is indeed temporary until Opaque pointers are here.
The problem has been stated last time in D99051 <https://reviews.llvm.org/D99051> by @ruiling:
https://godbolt.org/z/x7E1EjWvv, i.e. given the same integer,
there can be any number of pointers `inttoptr`'d from it,
and passes won't be able to tell that they are identical.

@dblaikie @t.p.northover can anyone comment on the Opaque Pointers progress? Is there a checklist somewhere?



================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp:278-280
+  if (firstOp == Instruction::IntToPtr && secondOp == Instruction::BitCast)
+    Res = 0;
+
----------------
ruiling wrote:
> If we want to disable int2ptr + bitcast unconditionally, then why not directly make it in CastInst::isEliminableCastPair()?
Because technically that is still legal, much like changing integer types of the `inttoptr`/`ptrtoint`,
which also aren't prohibited in `isEliminableCastPair()`.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp:1949-1953
+  if (CI.getType() != BytePtrTy) {
+    Value *P = Builder.CreateIntToPtr(CI.getOperand(0), BytePtrTy);
+    return new BitCastInst(P, CI.getType());
+  }
+
----------------
ruiling wrote:
> The idea here sounds good to me, but seems causing some new problems for the regression tests. I am not sure the whether the regressions are easy to fix?
FWIW all the problems are temporary until LLVM IR is migrated to typeless pointer types.


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