Fix 128-bit non-native integers comparison

Author: antoyo

Readme.md

@@ -113,6 +113,8 @@ $ LIBRARY_PATH=$(cat gcc_path) LD_LIBRARY_PATH=$(cat gcc_path) rustc +$(cat $CG_
     <dd>Display the time it took to perform codegen for a crate</dd>
     <dt>CG_RUSTFLAGS</dt>
     <dd>Send additional flags to rustc. Can be used to build the sysroot without unwinding by setting `CG_RUSTFLAGS=-Cpanic=abort`.</dd>
+    <dt>CG_GCCJIT_DUMP_TO_FILE</dt>
+    <dd>Dump a C-like representation to /tmp/gccjit_dumps and enable debug info in order to debug this C-like representation.</dd>
 </dl>
 
 ## Licensing

src/int.rs

@@ -353,23 +353,63 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
         (res.dereference(None).to_rvalue(), overflow)
     }
 
-    pub fn gcc_icmp(&self, op: IntPredicate, mut lhs: RValue<'gcc>, mut rhs: RValue<'gcc>) -> RValue<'gcc> {
+    pub fn gcc_icmp(&mut self, op: IntPredicate, mut lhs: RValue<'gcc>, mut rhs: RValue<'gcc>) -> RValue<'gcc> {
         let a_type = lhs.get_type();
         let b_type = rhs.get_type();
         if self.is_non_native_int_type(a_type) || self.is_non_native_int_type(b_type) {
-            let signed = a_type.is_compatible_with(self.i128_type);
-            let sign =
-                if signed {
-                    ""
-                }
-                else {
-                    "u"
-                };
-            let func_name = format!("__{}cmpti2", sign);
-            let param_a = self.context.new_parameter(None, a_type, "a");
-            let param_b = self.context.new_parameter(None, b_type, "b");
-            let func = self.context.new_function(None, FunctionType::Extern, self.int_type, &[param_a, param_b], func_name, false);
-            let cmp = self.context.new_call(None, func, &[lhs, rhs]);
+            // This algorithm is based on compiler-rt's __cmpti2:
+            // https://github.com/llvm-mirror/compiler-rt/blob/f0745e8476f069296a7c71accedd061dce4cdf79/lib/builtins/cmpti2.c#L21
+            let result = self.current_func().new_local(None, self.int_type, "icmp_result");
+            let block1 = self.current_func().new_block("block1");
+            let block2 = self.current_func().new_block("block2");
+            let block3 = self.current_func().new_block("block3");
+            let block4 = self.current_func().new_block("block4");
+            let block5 = self.current_func().new_block("block5");
+            let block6 = self.current_func().new_block("block6");
+            let block7 = self.current_func().new_block("block7");
+            let block8 = self.current_func().new_block("block8");
+            let after = self.current_func().new_block("after");
+
+            let native_int_type = a_type.dyncast_array().expect("get element type");
+            // NOTE: cast low to its unsigned type in order to perform a comparison correctly (e.g.
+            // the sign is only on high).
+            let unsigned_type = native_int_type.to_unsigned(&self.cx);
+
+            let lhs_low = self.context.new_cast(None, self.low(lhs), unsigned_type);
+            let rhs_low = self.context.new_cast(None, self.low(rhs), unsigned_type);
+
+            let condition = self.context.new_comparison(None, ComparisonOp::LessThan, self.high(lhs), self.high(rhs));
+            self.llbb().end_with_conditional(None, condition, block1, block2);
+
+            block1.add_assignment(None, result, self.context.new_rvalue_zero(self.int_type));
+            block1.end_with_jump(None, after);
+
+            let condition = self.context.new_comparison(None, ComparisonOp::GreaterThan, self.high(lhs), self.high(rhs));
+            block2.end_with_conditional(None, condition, block3, block4);
+
+            block3.add_assignment(None, result, self.context.new_rvalue_from_int(self.int_type, 2));
+            block3.end_with_jump(None, after);
+
+            let condition = self.context.new_comparison(None, ComparisonOp::LessThan, lhs_low, rhs_low);
+            block4.end_with_conditional(None, condition, block5, block6);
+
+            block5.add_assignment(None, result, self.context.new_rvalue_zero(self.int_type));
+            block5.end_with_jump(None, after);
+
+            let condition = self.context.new_comparison(None, ComparisonOp::GreaterThan, lhs_low, rhs_low);
+            block6.end_with_conditional(None, condition, block7, block8);
+
+            block7.add_assignment(None, result, self.context.new_rvalue_from_int(self.int_type, 2));
+            block7.end_with_jump(None, after);
+
+            block8.add_assignment(None, result, self.context.new_rvalue_one(self.int_type));
+            block8.end_with_jump(None, after);
+
+            // NOTE: since jumps were added in a place rustc does not expect, the current block in the
+            // state need to be updated.
+            self.switch_to_block(after);
+
+            let cmp = result.to_rvalue();
             let (op, limit) =
                 match op {
                     IntPredicate::IntEQ => {