fix(linter/tree-shaking): correct the calculation of >>, << and `…

…>>>` (#4932) fixes: #4914
oxc-project · Aug 16, 2024 · 508644a · 508644a
1 parent 80d0d1f
commit 508644a
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Showing 2 changed files with 51 additions and 18 deletions.
diff --git a/crates/oxc_codegen/Cargo.toml b/crates/oxc_codegen/Cargo.toml
@@ -28,10 +28,10 @@ oxc_sourcemap = { workspace = true }
 oxc_mangler   = { workspace = true }
 oxc_index     = { workspace = true }
 
-bitflags   = { workspace = true }
-nonmax     = { workspace = true }
-once_cell  = { workspace = true }
-daachorse  = { workspace = true }
+bitflags  = { workspace = true }
+nonmax    = { workspace = true }
+once_cell = { workspace = true }
+daachorse = { workspace = true }
 
 [dev-dependencies]
 oxc_parser = { workspace = true }

diff --git a/crates/oxc_linter/src/utils/tree_shaking.rs b/crates/oxc_linter/src/utils/tree_shaking.rs
@@ -420,12 +420,19 @@ pub fn calculate_binary_operation(op: BinaryOperator, left: Value, right: Value)
         }
 
         BinaryOperator::ShiftRightZeroFill => match (left, right) {
+            // <https://tc39.es/ecma262/#sec-numeric-types-number-unsignedRightShift>
             (Value::Number(a), Value::Number(b)) => {
-                if b >= a {
-                    Value::Number(0.0)
-                } else {
-                    Value::Number(f64::from((a as u32) >> (b as u32)))
-                }
+                // Casting between two integers of the same size (e.g. i32 -> u32) is a no-op
+                let a = a as i32;
+                let b = b as i32;
+                // 1. Let lNum be ! ToUint32(x).
+                let l_num = a as u32;
+                // 2. Let rNum be ! ToUint32(y).
+                let r_num = b as u32;
+                // 3. Let shiftCount be ℝ(rNum) modulo 32.
+                let shift_count = r_num % 32;
+                // 4. Return the result of performing a zero-filling right shift of lNum by shiftCount bits.
+                Value::Number(f64::from(l_num >> shift_count))
             }
             _ => Value::Unknown,
         },
@@ -450,18 +457,33 @@ pub fn calculate_binary_operation(op: BinaryOperator, left: Value, right: Value)
             _ => Value::Unknown,
         },
         BinaryOperator::ShiftLeft => match (left, right) {
+            // <https://tc39.es/ecma262/#sec-numeric-types-number-leftShift>
             (Value::Number(a), Value::Number(b)) => {
-                // NOTE: could overflow, in which case node produces `a`
-                if b >= 32.0 {
-                    Value::Number(a)
-                } else {
-                    Value::Number(f64::from((a as i32) << (b as i32)))
-                }
+                // 1. Let lNum be ! ToInt32(x).
+                let l_num = a as i32;
+                // 2. Let rNum be ! ToUint32(y).
+                let r_num = b as i32;
+                let r_num = r_num as u32;
+                // 3. Let shiftCount be ℝ(rNum) modulo 32.
+                let shift_count = r_num % 32;
+                // 4. Return the result of left shifting lNum by shiftCount bits.
+                Value::Number(f64::from(l_num << shift_count))
             }
             _ => Value::Unknown,
         },
         BinaryOperator::ShiftRight => match (left, right) {
-            (Value::Number(a), Value::Number(b)) => Value::Number(f64::from(a as i32 >> b as i32)),
+            // <https://tc39.es/ecma262/#sec-numeric-types-number-signedRightShift>
+            (Value::Number(a), Value::Number(b)) => {
+                // 1. Let lNum be ! ToInt32(x).
+                let l_num = a as i32;
+                // 2. Let rNum be ! ToUint32(y).
+                let r_num = b as i32;
+                let r_num = r_num as u32;
+                // 3. Let shiftCount be ℝ(rNum) modulo 32.
+                let shift_count = r_num % 32;
+                // 4. Return the result of performing a sign-extending right shift of lNum by shiftCount bits. The most significant bit is propagated. The mathematical value of the result is exactly representable as a 32-bit two's complement bit string.i
+                Value::Number(f64::from(l_num >> shift_count))
+            }
             _ => Value::Unknown,
         },
         BinaryOperator::In | BinaryOperator::Instanceof => Value::Unknown,
@@ -601,19 +623,30 @@ fn test_calculate_binary_operation() {
     assert_eq!(fun(op, Value::Number(1.0), Value::Number(0.0),), Value::Number(1.0));
     assert_eq!(fun(op, Value::Number(1.0), Value::Number(2.0),), Value::Number(4.0));
     assert_eq!(fun(op, Value::Number(1.0), Value::Number(31.0),), Value::Number(-2_147_483_648.0));
-    assert_eq!(fun(op, Value::Number(1.0), Value::Number(f64::MAX),), Value::Number(1.0));
+    assert_eq!(
+        fun(op, Value::Number(1.0), Value::Number(f64::MAX),),
+        Value::Number(-2_147_483_648.0)
+    );
+    assert_eq!(fun(op, Value::Number(-5.0), Value::Number(2.0),), Value::Number(-20.0));
 
     // ">>",
     let op = BinaryOperator::ShiftRight;
     assert_eq!(fun(op, Value::Number(4.0), Value::Number(2.0),), Value::Number(1.0));
+    // issue: https://github.com/oxc-project/oxc/issues/4914
+    assert_eq!(fun(op, Value::Number(4.0), Value::Number(49.0)), Value::Number(0.0));
+    assert_eq!(fun(op, Value::Number(-5.0), Value::Number(2.0),), Value::Number(-2.0));
 
     // ">>>",
     let op = BinaryOperator::ShiftRightZeroFill;
     assert_eq!(fun(op, Value::Number(0.0), Value::Number(0.0),), Value::Number(0.0));
     assert_eq!(fun(op, Value::Number(1.0), Value::Number(0.0),), Value::Number(1.0));
     assert_eq!(fun(op, Value::Number(4.0), Value::Number(2.0),), Value::Number(1.0));
     assert_eq!(fun(op, Value::Number(2.0), Value::Number(4.0),), Value::Number(0.0));
-    assert_eq!(fun(op, Value::Number(4096.0), Value::Number(4096.0)), Value::Number(0.0));
+    assert_eq!(fun(op, Value::Number(4096.0), Value::Number(4096.0)), Value::Number(4096.0));
+    assert_eq!(fun(op, Value::Number(4096.0), Value::Number(1024.0)), Value::Number(4096.0));
+    assert_eq!(fun(op, Value::Number(4096.0), Value::Number(33.0)), Value::Number(2048.0));
+    assert_eq!(fun(op, Value::Number(4.0), Value::Number(49.0)), Value::Number(0.0));
+    assert_eq!(fun(op, Value::Number(-5.0), Value::Number(2.0)), Value::Number(1_073_741_822.0));
 
     // "%",
     let op = BinaryOperator::Remainder;