a416267a5f
This patch is episode three of the middle end implementation for the coroutine HALO improvement project published on discourse: https://discourse.llvm.org/t/language-extension-for-better-more-deterministic-halo-for-c-coroutines/80044 After we attribute the calls to some coroutines as "coro_elide_safe" in the C++ FE and creating a `noalloc` ramp function, we use a new middle end pass to move the call to coroutines to the noalloc variant. This pass should be run after CoroSplit. For each node we process in CoroSplit, we look for its callers and replace the attributed ones in presplit coroutines to the noalloc one. The transformed `noalloc` ramp function will also require a frame pointer to a block of memory it can use as an activation frame. We allocate this on the caller's frame with an alloca. Please note that we cannot safely transform such attributed calls in post-split coroutines due to memory lifetime reasons. The CoroSplit pass is responsible for creating the coroutine frame spills for all the allocas in the coroutine. Therefore it will be unsafe to create new allocas like this one in post-split coroutines. This happens relatively rarely because CGSCC performs the passes on the callees before the caller. However, if multiple coroutines coexist in one SCC, this situation does happen (and prevents us from having potentially unbound frame size due to recursion.) You can find episode 1: Clang FE of this patch series at https://github.com/llvm/llvm-project/pull/99282 Episode 2: CoroSplit at https://github.com/llvm/llvm-project/pull/99283
13 KiB
13 KiB