Fix integer overflow for widening addition

PiperOrigin-RevId: 879258854
Change-Id: Ied83d7ca7609a21ce10ee466e96131030f7cdd37

riscv/riscv_i_instructions.cc

diff --git a/riscv/riscv_i_instructions.cc b/riscv/riscv_i_instructions.cc
index baf0afe..ecdd6bf 100644
--- a/riscv/riscv_i_instructions.cc
+++ b/riscv/riscv_i_instructions.cc
@@ -201,7 +201,7 @@
 void RiscVIAddw(const Instruction* instruction) {
   RiscVBinaryOp<RegisterType, IntReg, NarrowIntReg>(
       instruction, [](NarrowIntReg a, NarrowIntReg b) {
-        IntReg c = static_cast<IntReg>(a + b);
+        IntReg c = static_cast<IntReg>(a) + static_cast<IntReg>(b);
         return c;
       });
 }