[llvm] [FunctionAttrs] deduce attr `cold` on functions if all CG paths call a `cold` function (PR #101298)

[Nikita Popov via llvm-commits]

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@@ -1760,6 +1761,70 @@ static void addNoReturnAttrs(const SCCNodeSet &SCCNodes,
   }
 }
 
+static bool
+allBBPathsGoThroughCold(BasicBlock *BB,
+                        SmallDenseMap<BasicBlock *, bool, 16> &Visited) {
+  // If BB contains a cold callsite this path through the CG is cold.
+  if (any_of(*BB, [](Instruction &I) {
+        if (auto *CB = dyn_cast<CallBase>(&I))
+          return CB->hasFnAttr(Attribute::Cold);
+        return false;
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nikic wrote:

I'd add a note that this assumes throwing an diverging code paths are cold, which is why this does not check for guaranteed-to-transfer.

https://github.com/llvm/llvm-project/pull/101298