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Function should store Arguments contiguously not in an iplist #16910

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llvmbot opened this issue Jul 4, 2013 · 0 comments
Closed

Function should store Arguments contiguously not in an iplist #16910

llvmbot opened this issue Jul 4, 2013 · 0 comments
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bugzilla llvm:core

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@llvmbot llvmbot commented Jul 4, 2013

Bugzilla Link 16536
Resolution FIXED
Resolved on Apr 30, 2020 13:05
Version trunk
OS Linux
Reporter LLVM Bugzilla Contributor
CC @ekatz
Fixed by commit(s) rL298105

Extended Description

Functions are created separately from their Argument list, which is stored as a linked list. The Argument list is inseparably tied to the type of the function, which is an immutable property of the function when created. We aren't benefiting from giving Argument lists efficient insertion you need to destroy and recreate the whole Function regardless.

Instead, we should contiguously allocate the space for the arguments and construct them when the function is created, and destroy them when the function is destroyed.

Pros:

  • Efficient random access to the n-th Argument*.
  • One fewer allocation for the function and arguments.
  • Saves two pointers per Argument, since there's no more ilist_node<> for each one.
  • Argument::getArgNo() could be reimplemented as O(1) using pointer subtraction instead of the present O(n) list walk.

Cons:

  • No longer be efficient to swap two same-typed arguments.
  • No longer lazily create the argument list.
  • No longer support polymorphic Arguments (in case we do already).

This gives us the nice property that we could walk from a callsite parameter operand number to a function's n-th argument in constant time.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 9, 2021
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