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

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:2440
+      assert(NewCI->isMustTailCall() &&
+             "replaced musttail call with non-musttail call");
+      (void)NewCI;
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I don't understand this assertion.  There are two possibilities for simplification:

1. We replace a call with some existing value.
2. We replace a call with another new call.

For (1), this assertion doesn't make sense: we don't have a call.  For (2), we probably can't safely do the replacement in general; musttail has a bunch of restrictions, and the replacement call might not satisfy them.


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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;
----------------
xbolva00 wrote:
> Is it worth it at all?
> 
> I would just bail out libcall simplifier for musttail CIs
I agree; musttail calls should be rare enough that it isn't a big deal to just skip libcall simplification completely


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https://reviews.llvm.org/D107872