[llvm] [Inliner] Don't count a call penalty for foldable __memcpy_chk and similar (PR #117876)

[Marina Taylor via llvm-commits]

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@@ -2260,6 +2271,48 @@ bool CallAnalyzer::simplifyCallSite(Function *F, CallBase &Call) {
   return false;
 }
 
+bool CallAnalyzer::isLoweredToCall(Function *F, CallBase &Call) {
+  // Calls to memcpy with a known constant size 1/2/4/8 should not incur a call
+  // penalty, as the calls will be folded away by InstCombine. This is only
+  // really relevant on platforms whose headers redirect memcpy to __memcpy_chk
+  // (e.g. Mac), as other platforms use memcpy intrinsics, which are already
+  // exempt from the call penalty.
+  if (GetTLI) {
+    auto TLI = GetTLI(*F);
+    LibFunc LF;
+    if (TLI.getLibFunc(*F, LF) && TLI.has(LF)) {
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citymarina wrote:

In what way do you suggest to exit? The ultimate fallback at the end of the function is the `TTI`, so neither a quick `return true` nor `return false` would be ideal here.

https://github.com/llvm/llvm-project/pull/117876