[PATCH] D107872: [SimplifyLibCalls] propagate tail/musttail/notail flags on CallInsts

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:2435-2444
   if (Value *With = Simplifier.optimizeCall(CI, Builder)) {
+    if (CI->isMustTailCall()) {
+      auto *NewCI = dyn_cast<CallInst>(With);
+      assert(NewCI && "replaced musttail call with non-CallInst");
+      assert(NewCI->isMustTailCall() &&
+             "replaced musttail call with non-musttail call");
+      (void)NewCI;
----------------
nickdesaulniers wrote:
> Thinking about this overnight...if this is the one place where replacement occurs, then why don't I just copy over the tail call kind here, rather than use the adapter in multiple locations in LibCallSimplifier? As I've already demonstrating, this approach is error prone; perhaps I could "do the work" here. Then we wouldn't need the asserts here, and this becomes a smaller change.  Let me give that a shot and see if there's something I'm missing here as to why that can't be done.
This is what was the idea of https://reviews.llvm.org/D89249 but check @efriedma 's comment. First point is problematic.

For second and third:

"A lot of combines create calls, but return some other value."

I think this is not a issue. We simply fail to preserve this info, but what is problematic .. musttail. I still think if CI->isMustTailCall() == true, than we should throw away NewCI if NewCI is not a CallInst.

"For the floating-point routines, we probably want to add "tail" unconditionally."

Yeah, probably okay and can be here. Not sure how to correctly detect it, maybe TLI.has(rountine) && rountine->getType() is FP?




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Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:1162
 Value *LibCallSimplifier::optimizeMemPCpy(CallInst *CI, IRBuilderBase &B) {
+  if (CI->isMustTailCall())
+    return nullptr;
----------------
Is it worth it at all?

I would just bail out libcall simplifier for musttail CIs


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D107872/new/

https://reviews.llvm.org/D107872