From 10971912e87e0ab10e1f7c6e9da8086f11ced68a Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Mon, 2 May 2022 23:00:12 +0200
Subject: [PATCH] rv64 implement muldi3 intrinsic

Implement the __muldi3 intrinsic to prevent infinite recursion during
multiplication on rv64 without the 'm' extension.
---
 library/compiler-builtins/src/int/mul.rs        |  1 +
 library/compiler-builtins/src/lib.rs            |  4 ++--
 .../src/{riscv32.rs => riscv.rs}                | 17 +++++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)
 rename library/compiler-builtins/src/{riscv32.rs => riscv.rs} (54%)

diff --git a/library/compiler-builtins/src/int/mul.rs b/library/compiler-builtins/src/int/mul.rs
index a5238eeac70e..37eb03ec054f 100644
--- a/library/compiler-builtins/src/int/mul.rs
+++ b/library/compiler-builtins/src/int/mul.rs
@@ -100,6 +100,7 @@ impl_signed_mulo!(i128_overflowing_mul, i128, u128);
 intrinsics! {
     #[maybe_use_optimized_c_shim]
     #[arm_aeabi_alias = __aeabi_lmul]
+    #[cfg(not(target_arch = "riscv64"))]
     pub extern "C" fn __muldi3(a: u64, b: u64) -> u64 {
         a.mul(b)
     }
diff --git a/library/compiler-builtins/src/lib.rs b/library/compiler-builtins/src/lib.rs
index 9ca72bc20f4e..009923d27e5b 100644
--- a/library/compiler-builtins/src/lib.rs
+++ b/library/compiler-builtins/src/lib.rs
@@ -60,8 +60,8 @@ pub mod arm;
 ))]
 pub mod arm_linux;
 
-#[cfg(any(target_arch = "riscv32"))]
-pub mod riscv32;
+#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
+pub mod riscv;
 
 #[cfg(target_arch = "x86")]
 pub mod x86;
diff --git a/library/compiler-builtins/src/riscv32.rs b/library/compiler-builtins/src/riscv.rs
similarity index 54%
rename from library/compiler-builtins/src/riscv32.rs
rename to library/compiler-builtins/src/riscv.rs
index 9a3c1714c1f0..d9a65e200745 100644
--- a/library/compiler-builtins/src/riscv32.rs
+++ b/library/compiler-builtins/src/riscv.rs
@@ -1,6 +1,7 @@
 intrinsics! {
     // Implementation from gcc
     // https://raw.githubusercontent.com/gcc-mirror/gcc/master/libgcc/config/epiphany/mulsi3.c
+    #[cfg(target_arch = "riscv32")]
     pub extern "C" fn __mulsi3(a: u32, b: u32) -> u32 {
         let (mut a, mut b) = (a, b);
         let mut r = 0;
@@ -15,4 +16,20 @@ intrinsics! {
 
         r
     }
+
+    #[cfg(target_arch = "riscv64")]
+    pub extern "C" fn __muldi3(a: u64, b: u64) -> u64 {
+        let (mut a, mut b) = (a, b);
+        let mut r = 0;
+
+        while a > 0 {
+            if a & 1 > 0 {
+                r += b;
+            }
+            a >>= 1;
+            b <<= 1;
+        }
+
+        r
+    }
 }