================
@@ -2282,6 +2282,15 @@ Instruction
*InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
if (MadeChange)
return &GEP;
+ // Canonicalize constant GEPs to i8 type.
----------------
bjope wrote:
FWIW, this is a bit interesting downstream with non-8-bit addressing units :-)
Today i8 would be quite rare as GEP type for us as it is smaller than the
addressing unit size. But I figure that canonicalizing to some other type
downstream could end up as a lot of work (or lots of missed optimizations).
Afaict accumulateConstantOffset is returning an offset that depends on
TypeStoreSize. So as long as this is used in a way so that the address still
would be given by `baseptr + DL.getTypeStoreSize(i8) * Offset` and not
`baseptr + 8 * Offset` , then I guess things will be fine (i.e not assuming
that the offset is an 8-bit offset).
As far as I can tell you could just as well have picked i1 instead of i8 (given
that `DL.getTypeStoreSize(i1)==DL.getTypeStoreSize(i8)`). That would probably
look confusing, but that is what happens for us when using i8 as type as we
can't address individual octets.
(I also see this as a reminder for looking at the ptradd RFC to understand how
that will impact us, so that we are prepared for that.)
https://github.com/llvm/llvm-project/pull/68882
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