refactor : get rid of std::abs() & improve comments

Author: ge28boj

mlir/lib/Dialect/PDL/IR/Builtins.cpp

@@ -107,15 +107,17 @@ LogicalResult static unaryOp(PatternRewriter &rewriter, PDLResultList &results,
           return failure();
 
         results.push_back(rewriter.getIntegerAttr(
-            integerType, std::abs(operandIntAttr.getSInt())));
+            integerType, operandIntAttr.getValue().abs()));
         return success();
       }
       if (integerType.isSignless()) {
+        // Overflow should not be checked.
+        // Otherwise the purpose of signless integer is meaningless.
         results.push_back(rewriter.getIntegerAttr(
-            integerType, std::abs(operandIntAttr.getInt())));
+            integerType, operandIntAttr.getValue().abs()));
         return success();
       }
-      // If unsigned, don't do anything
+      // If unsigned, do nothing
       results.push_back(operandIntAttr);
       return success();
     } else {
@@ -163,9 +165,10 @@ LogicalResult static unaryOp(PatternRewriter &rewriter, PDLResultList &results,
           operandFloatAttr.getType(),
           (double)operandFloatAttr.getValue().getExactLog2()));
     } else if constexpr (T == UnaryOpKind::abs) {
-      results.push_back(rewriter.getFloatAttr(
-          operandFloatAttr.getType(),
-          std::abs(operandFloatAttr.getValue().convertToFloat())));
+      auto resultVal = operandFloatAttr.getValue();
+      resultVal.clearSign();
+      results.push_back(
+          rewriter.getFloatAttr(operandFloatAttr.getType(), resultVal));
     } else {
       llvm::llvm_unreachable_internal(
           "encountered an unsupported unary operator");

mlir/lib/Tools/PDLL/Parser/Lexer.h

@@ -81,11 +81,11 @@ class Token {
     equal_arrow,
     semicolon,
     /// Paired punctuation.
+    add,
+    sub,
     mul,
     div,
     mod,
-    add,
-    sub,
     log2,
     exp2,
     abs,

mlir/unittests/Dialect/PDL/BuiltinTest.cpp

@@ -752,6 +752,19 @@ TEST_F(BuiltinTest, abs) {
         7);
   }
 
+  // signless integer: edge case -128
+  // Overflow should not be checked
+  // otherwise the purpose of signless integer is meaningless
+  {
+    auto value = rewriter.getI8IntegerAttr(-128);
+    TestPDLResultList results(1);
+    EXPECT_TRUE(builtin::abs(rewriter, results, {value}).succeeded());
+    auto result = results.getResults()[0];
+    EXPECT_EQ(
+        cast<IntegerAttr>(result.cast<Attribute>()).getValue().getSExtValue(),
+        -128);
+  }
+
   // float
   {
     auto value = rewriter.getF32FloatAttr(-1.0);