[TLI] Add support for inferring attr `cold`/`noreturn` on `std::terminate` and `__cxa_throw`

These functions are both inherently on the error path so `cold` seems
appropriate. `noreturn` is definitional.

Closes #101622

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
index c23d53f..b0da198 100644
--- a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
@@ -50,6 +50,7 @@ STATISTIC(NumNoUndef, "Number of function returns inferred as noundef returns");
 STATISTIC(NumReturnedArg, "Number of arguments inferred as returned");
 STATISTIC(NumWillReturn, "Number of functions inferred as willreturn");
 STATISTIC(NumCold, "Number of functions inferred as cold");
+STATISTIC(NumNoReturn, "Number of functions inferred as no return");
 
 static bool setDoesNotAccessMemory(Function &F) {
   if (F.doesNotAccessMemory())
@@ -67,6 +68,14 @@ static bool setIsCold(Function &F) {
   return true;
 }
 
+static bool setNoReturn(Function &F) {
+  if (F.hasFnAttribute(Attribute::NoReturn))
+    return false;
+  F.addFnAttr(Attribute::NoReturn);
+  ++NumNoReturn;
+  return true;
+}
+
 static bool setOnlyAccessesInaccessibleMemory(Function &F) {
   if (F.onlyAccessesInaccessibleMemory())
     return false;
@@ -1103,6 +1112,15 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_abort:
     Changed |= setIsCold(F);
     break;
+  case LibFunc_terminate:
+    Changed |= setIsCold(F);
+    Changed |= setNoReturn(F);
+    break;
+  case LibFunc_cxa_throw:
+    Changed |= setIsCold(F);
+    Changed |= setNoReturn(F);
+    // Don't add `nofree` on `__cxa_throw`
+    return Changed;
   // int __nvvm_reflect(const char *)
   case LibFunc_nvvm_reflect:
     Changed |= setRetAndArgsNoUndef(F);