[llvm] MathExtras: MulOverflow: use builtin when available (PR #95046)

[Arjun P via llvm-commits]

https://github.com/Superty created https://github.com/llvm/llvm-project/pull/95046

This matches the other two functions AddOverflow and SubOverflow.

>From be441a78de17cbfef798a620769d21307cdf84f2 Mon Sep 17 00:00:00 2001
From: Arjun P <arjunpitchanathan at gmail.com>
Date: Mon, 10 Jun 2024 22:17:58 +0100
Subject: [PATCH] MathExtras: MulOverflow: use builtin when available

---
 llvm/include/llvm/Support/MathExtras.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
index f0e4ee534ece3..adb5ba6e3dcc2 100644
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -635,6 +635,9 @@ std::enable_if_t<std::is_signed_v<T>, T> SubOverflow(T X, T Y, T &Result) {
 /// result, returning true if an overflow ocurred.
 template <typename T>
 std::enable_if_t<std::is_signed_v<T>, T> MulOverflow(T X, T Y, T &Result) {
+#if __has_builtin(__builtin_mul_overflow)
+  return __builtin_mul_overflow(X, Y, &Result);
+#else
   // Perform the unsigned multiplication on absolute values.
   using U = std::make_unsigned_t<T>;
   const U UX = X < 0 ? (0 - static_cast<U>(X)) : static_cast<U>(X);
@@ -656,6 +659,7 @@ std::enable_if_t<std::is_signed_v<T>, T> MulOverflow(T X, T Y, T &Result) {
     return UX > (static_cast<U>(std::numeric_limits<T>::max()) + U(1)) / UY;
   else
     return UX > (static_cast<U>(std::numeric_limits<T>::max())) / UY;
+#endif
 }
 
 } // namespace llvm