[PATCH] D94248: [NFC][FuncAttrs] Add comment on why we look for noreturn calls

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks created this revision.
aeubanks added a reviewer: reames.
Herald added a subscriber: hiraditya.
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Followup to https://reviews.llvm.org/D93946.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D94248

Files:
  llvm/lib/Transforms/IPO/FunctionAttrs.cpp


Index: llvm/lib/Transforms/IPO/FunctionAttrs.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -1398,6 +1398,11 @@
 
 // A basic block can only return if it terminates with a ReturnInst and does not
 // contain calls to noreturn functions.
+// If we could assume that something like SimplifyCFG would always run before
+// FunctionAttrs and replace code after instructions that don't return with
+// unreachable, we would only need to look at the terminator. However, that's
+// not always true; for example the new PM's CGSCC pipeline first runs
+// FunctionAttrs, then function simplification passes.
 static bool basicBlockCanReturn(BasicBlock &BB) {
   if (!isa<ReturnInst>(BB.getTerminator()))
     return false;


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