[PATCH] D89980: [hip] Remove kernel argument coercion.

[Michael Liao via Phabricator via cfe-commits]

hliao added a comment.

In D89980#2368506 <https://reviews.llvm.org/D89980#2368506>, @arsenm wrote:

> I think this is a dead end approach. I don't see the connection to the original problem you are trying to solve. Can you send me an IR testcase that this is supposed to help?

That's probably commonly known. If we pass an aggregate parameter directly by value and dynamically index it late, that `alloca` cannot be promoted as that aggregate value in LLVM IR cannot be dynamically indexed. For example,

  struct S {
     int a[100];
     int n;
  };
  
  int foo(S s) {
    return s.a[s.n];
  }

If the underlying ABI chooses to pass `s` directly by value, we have the following pseudo IR.

  %s = alloca S
  ; store `s` value into %s as the parameter is treated as a local variable by filling its initial value from LLVM IR parameter.
  ...
  ; regular parameter access through %s with dynamic indices

that `store` from the parameter from LLVM IR is an aggregate value store. Later, when %s is to be promoted, as it's once dynamically indexed, we cannot promote it as dynamic index on aggregate values is not representable in LLVM IR.

In contrast, if a parameter is passed by value indirectly, that `store` is replaced with a `memcpy`. It's straightforward to promote '%s' as they are all memory operands of the same layout.

If you need detailed IR, I may post here for your reference.


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https://reviews.llvm.org/D89980