[RISCV-V] Provide muldi3 builtin assembly implementation

Provides an assembly implementation of muldi3 for RISC-V, to solve bug 43388.
Since the implementation is the same as for mulsi3, that code was moved to
`riscv/int_mul_impl.inc` and is now reused by both `mulsi3.S` and `muldi3.S`.

Differential Revision: https://reviews.llvm.org/D80465

(cherry picked from commit e31ccee)

Author: kamleshbhalui

compiler-rt/lib/builtins/riscv/int_mul_impl.inc

@@ -0,0 +1,31 @@
+//===-- int_mul_impl.inc - Integer multiplication -------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Helpers used by __mulsi3, __muldi3.
+//
+//===----------------------------------------------------------------------===//
+
+#if !defined(__riscv_mul)
+	.text
+	.align 2
+
+	.globl __mulxi3
+	.type  __mulxi3, @function
+__mulxi3:
+	mv     a2, a0
+	mv     a0, zero
+.L1:
+	andi   a3, a1, 1
+	beqz   a3, .L2
+	add    a0, a0, a2
+.L2:
+	srli   a1, a1, 1
+	slli   a2, a2, 1
+	bnez   a1, .L1
+	ret
+#endif

compiler-rt/lib/builtins/riscv/muldi3.S

@@ -0,0 +1,11 @@
+//===--- muldi3.S - Integer multiplication routines -----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#if __riscv_xlen == 64
+#define __mulxi3 __muldi3
+#include "int_mul_impl.inc"
+#endif

compiler-rt/lib/builtins/riscv/mulsi3.S

@@ -1,27 +1,12 @@
-//===--- mulsi3.S - Integer multiplication routines routines ---===//
+//===--- mulsi3.S - Integer multiplication routines -----------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-#if !defined(__riscv_mul) && __riscv_xlen == 32
-	.text
-	.align 2
-
-	.globl __mulsi3
-	.type  __mulsi3, @function
-__mulsi3:
-	mv     a2, a0
-	mv     a0, zero
-.L1:
-	andi   a3, a1, 1
-	beqz   a3, .L2
-	add    a0, a0, a2
-.L2:
-	srli   a1, a1, 1
-	slli   a2, a2, 1
-	bnez   a1, .L1
-	ret
+#if __riscv_xlen == 32
+#define __mulxi3 __mulsi3
+#include "int_mul_impl.inc"
 #endif