Merge pull request rust-lang#156 from yvt/fix-int-ops

Implement `saturating_{add, sub}` for non-native integer types

Author: antoyo

src/intrinsic/mod.rs

@@ -967,34 +967,55 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
     }
 
     fn saturating_add(&mut self, lhs: RValue<'gcc>, rhs: RValue<'gcc>, signed: bool, width: u64) -> RValue<'gcc> {
-        let func = self.current_func.borrow().expect("func");
-
+        let result_type = lhs.get_type();
         if signed {
-            // Algorithm from: https://stackoverflow.com/a/56531252/389119
-            let after_block = func.new_block("after");
-            let func_name =
-                match width {
-                    8 => "__builtin_add_overflow",
-                    16 => "__builtin_add_overflow",
-                    32 => "__builtin_sadd_overflow",
-                    64 => "__builtin_saddll_overflow",
-                    128 => "__builtin_add_overflow",
-                    _ => unreachable!(),
-                };
-            let overflow_func = self.context.get_builtin_function(func_name);
-            let result_type = lhs.get_type();
+            // Based on algorithm from: https://stackoverflow.com/a/56531252/389119
+            let func = self.current_func.borrow().expect("func");
             let res = func.new_local(None, result_type, "saturating_sum");
-            let overflow = self.overflow_call(overflow_func, &[lhs, rhs, res.get_address(None)], None);
+            let supports_native_type = self.is_native_int_type(result_type);
+            let overflow =
+                if supports_native_type {
+                    let func_name =
+                        match width {
+                            8 => "__builtin_add_overflow",
+                            16 => "__builtin_add_overflow",
+                            32 => "__builtin_sadd_overflow",
+                            64 => "__builtin_saddll_overflow",
+                            128 => "__builtin_add_overflow",
+                            _ => unreachable!(),
+                        };
+                    let overflow_func = self.context.get_builtin_function(func_name);
+                    self.overflow_call(overflow_func, &[lhs, rhs, res.get_address(None)], None)
+                }
+                else {
+                    let func_name =
+                        match width {
+                            128 => "__rust_i128_addo",
+                            _ => unreachable!(),
+                        };
+                    let param_a = self.context.new_parameter(None, result_type, "a");
+                    let param_b = self.context.new_parameter(None, result_type, "b");
+                    let result_field = self.context.new_field(None, result_type, "result");
+                    let overflow_field = self.context.new_field(None, self.bool_type, "overflow");
+                    let return_type = self.context.new_struct_type(None, "result_overflow", &[result_field, overflow_field]);
+                    let func = self.context.new_function(None, FunctionType::Extern, return_type.as_type(), &[param_a, param_b], func_name, false);
+                    let result = self.context.new_call(None, func, &[lhs, rhs]);
+                    let overflow = result.access_field(None, overflow_field);
+                    let int_result = result.access_field(None, result_field);
+                    self.llbb().add_assignment(None, res, int_result);
+                    overflow
+                };
 
             let then_block = func.new_block("then");
+            let after_block = func.new_block("after");
 
-            let unsigned_type = self.context.new_int_type(width as i32 / 8, false);
-            let shifted = self.context.new_cast(None, lhs, unsigned_type) >> self.context.new_rvalue_from_int(unsigned_type, width as i32 - 1);
-            let uint_max = self.context.new_unary_op(None, UnaryOp::BitwiseNegate, unsigned_type,
-                self.context.new_rvalue_from_int(unsigned_type, 0)
-            );
-            let int_max = uint_max >> self.context.new_rvalue_one(unsigned_type);
-            then_block.add_assignment(None, res, self.context.new_cast(None, shifted + int_max, result_type));
+            // Return `result_type`'s maximum or minimum value on overflow
+            // NOTE: convert the type to unsigned to have an unsigned shift.
+            let unsigned_type = result_type.to_unsigned(&self.cx);
+            let shifted = self.gcc_lshr(self.gcc_int_cast(lhs, unsigned_type), self.gcc_int(unsigned_type, width as i64 - 1));
+            let uint_max = self.gcc_not(self.gcc_int(unsigned_type, 0));
+            let int_max = self.gcc_lshr(uint_max, self.gcc_int(unsigned_type, 1));
+            then_block.add_assignment(None, res, self.gcc_int_cast(self.gcc_add(shifted, int_max), result_type));
             then_block.end_with_jump(None, after_block);
 
             self.llbb().end_with_conditional(None, overflow, then_block, after_block);
@@ -1007,19 +1028,18 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
         }
         else {
             // Algorithm from: http://locklessinc.com/articles/sat_arithmetic/
-            let res = lhs + rhs;
-            let res_type = res.get_type();
-            let cond = self.context.new_comparison(None, ComparisonOp::LessThan, res, lhs);
-            let value = self.context.new_unary_op(None, UnaryOp::Minus, res_type, self.context.new_cast(None, cond, res_type));
-            res | value
+            let res = self.gcc_add(lhs, rhs);
+            let cond = self.gcc_icmp(IntPredicate::IntULT, res, lhs);
+            let value = self.gcc_neg(self.gcc_int_cast(cond, result_type));
+            self.gcc_or(res, value)
         }
     }
 
     // Algorithm from: https://locklessinc.com/articles/sat_arithmetic/
     fn saturating_sub(&mut self, lhs: RValue<'gcc>, rhs: RValue<'gcc>, signed: bool, width: u64) -> RValue<'gcc> {
+        let result_type = lhs.get_type();
         if signed {
-            // Also based on algorithm from: https://stackoverflow.com/a/56531252/389119
-            let result_type = lhs.get_type();
+            // Based on algorithm from: https://stackoverflow.com/a/56531252/389119
             let func = self.current_func.borrow().expect("func");
             let res = func.new_local(None, result_type, "saturating_diff");
             let supports_native_type = self.is_native_int_type(result_type);
@@ -1059,6 +1079,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
             let then_block = func.new_block("then");
             let after_block = func.new_block("after");
 
+            // Return `result_type`'s maximum or minimum value on overflow
             // NOTE: convert the type to unsigned to have an unsigned shift.
             let unsigned_type = result_type.to_unsigned(&self.cx);
             let shifted = self.gcc_lshr(self.gcc_int_cast(lhs, unsigned_type), self.gcc_int(unsigned_type, width as i64 - 1));
@@ -1076,11 +1097,10 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
             res.to_rvalue()
         }
         else {
-            let res = lhs - rhs;
-            let comparison = self.context.new_comparison(None, ComparisonOp::LessThanEquals, res, lhs);
-            let comparison = self.context.new_cast(None, comparison, lhs.get_type());
-            let unary_op = self.context.new_unary_op(None, UnaryOp::Minus, comparison.get_type(), comparison);
-            self.and(res, unary_op)
+            let res = self.gcc_sub(lhs, rhs);
+            let comparison = self.gcc_icmp(IntPredicate::IntULE, res, lhs);
+            let value = self.gcc_neg(self.gcc_int_cast(comparison, result_type));
+            self.gcc_and(res, value)
         }
     }
 }