fix #3645: constant folding for < > <= >=

evanw · evanw · commit 555db48d3ddf · 2024-02-18T15:28:37.000-08:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -28,6 +28,21 @@
     }
     ```
 
+* Constant folding for JavaScript inequality operators ([#3645](https://github.com/evanw/esbuild/issues/3645))
+
+    This release introduces constant folding for the `< > <= >=` operators. The minifier will now replace these operators with `true` or `false` when both sides are compile-time numeric or string constants:
+
+    ```js
+    // Original code
+    console.log(1 < 2, '🍕' > '🧀')
+
+    // Old output (with --minify)
+    console.log(1<2,"🍕">"🧀");
+
+    // New output (with --minify)
+    console.log(!0,!1);
+    ```
+
 * Fix cross-platform non-determinism with CSS color space transformations ([#3650](https://github.com/evanw/esbuild/issues/3650))
 
     The Go compiler takes advantage of "fused multiply and add" (FMA) instructions on certain processors which do the operation `x*y + z` without intermediate rounding. This causes esbuild's CSS color space math to differ on different processors (currently `ppc64le` and `s390x`), which breaks esbuild's guarantee of deterministic output. To avoid this, esbuild's color space math now inserts a `float64()` cast around every single math operation. This tells the Go compiler not to use the FMA optimization.
diff --git a/internal/bundler_tests/snapshots/snapshots_dce.txt b/internal/bundler_tests/snapshots/snapshots_dce.txt
@@ -274,10 +274,10 @@ console.log([
   3 /* a */ % 6 /* b */,
   3 /* a */ ** 6 /* b */
 ], [
-  3 /* a */ < 6 /* b */,
-  3 /* a */ > 6 /* b */,
-  3 /* a */ <= 6 /* b */,
-  3 /* a */ >= 6 /* b */,
+  !0,
+  !1,
+  !0,
+  !1,
   3 /* a */ == 6 /* b */,
   3 /* a */ != 6 /* b */,
   3 /* a */ === 6 /* b */,
@@ -312,10 +312,10 @@ console.log([
   3 % 6,
   3 ** 6
 ], [
-  3 < 6,
-  3 > 6,
-  3 <= 6,
-  3 >= 6,
+  !0,
+  !1,
+  !0,
+  !1,
   3 == 6,
   3 != 6,
   3 === 6,
diff --git a/internal/js_ast/js_ast_helpers.go b/internal/js_ast/js_ast_helpers.go
@@ -1086,6 +1086,45 @@ func extractNumericValues(left Expr, right Expr) (float64, float64, bool) {
 	return 0, 0, false
 }
 
+func extractStringValue(data E) ([]uint16, bool) {
+	switch e := data.(type) {
+	case *EAnnotation:
+		return extractStringValue(e.Value.Data)
+
+	case *EInlinedEnum:
+		return extractStringValue(e.Value.Data)
+
+	case *EString:
+		return e.Value, true
+	}
+
+	return nil, false
+}
+
+func extractStringValues(left Expr, right Expr) ([]uint16, []uint16, bool) {
+	if a, ok := extractStringValue(left.Data); ok {
+		if b, ok := extractStringValue(right.Data); ok {
+			return a, b, true
+		}
+	}
+	return nil, nil, false
+}
+
+func stringCompareUCS2(a []uint16, b []uint16) int {
+	var n int
+	if len(a) < len(b) {
+		n = len(a)
+	} else {
+		n = len(b)
+	}
+	for i := 0; i < n; i++ {
+		if delta := int(a[i]) - int(b[i]); delta != 0 {
+			return delta
+		}
+	}
+	return len(a) - len(b)
+}
+
 func approximatePrintedIntCharCount(intValue float64) int {
 	count := 1 + (int)(math.Max(0, math.Floor(math.Log10(math.Abs(intValue)))))
 	if intValue < 0 {
@@ -1106,7 +1145,11 @@ func ShouldFoldBinaryArithmeticWhenMinifying(binary *EBinary) bool {
 		// are unlikely to result in larger output.
 		BinOpBitwiseAnd,
 		BinOpBitwiseOr,
-		BinOpBitwiseXor:
+		BinOpBitwiseXor,
+		BinOpLt,
+		BinOpGt,
+		BinOpLe,
+		BinOpGe:
 		return true
 
 	case BinOpAdd:
@@ -1221,6 +1264,38 @@ func FoldBinaryArithmetic(loc logger.Loc, e *EBinary) Expr {
 		if left, right, ok := extractNumericValues(e.Left, e.Right); ok {
 			return Expr{Loc: loc, Data: &ENumber{Value: float64(ToInt32(left) ^ ToInt32(right))}}
 		}
+
+	case BinOpLt:
+		if left, right, ok := extractNumericValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: left < right}}
+		}
+		if left, right, ok := extractStringValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: stringCompareUCS2(left, right) < 0}}
+		}
+
+	case BinOpGt:
+		if left, right, ok := extractNumericValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: left > right}}
+		}
+		if left, right, ok := extractStringValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: stringCompareUCS2(left, right) > 0}}
+		}
+
+	case BinOpLe:
+		if left, right, ok := extractNumericValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: left <= right}}
+		}
+		if left, right, ok := extractStringValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: stringCompareUCS2(left, right) <= 0}}
+		}
+
+	case BinOpGe:
+		if left, right, ok := extractNumericValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: left >= right}}
+		}
+		if left, right, ok := extractStringValues(e.Left, e.Right); ok {
+			return Expr{Loc: loc, Data: &EBoolean{Value: stringCompareUCS2(left, right) >= 0}}
+		}
 	}
 
 	return Expr{}
diff --git a/internal/js_parser/js_parser_test.go b/internal/js_parser/js_parser_test.go
@@ -4653,15 +4653,31 @@ func TestMangleBinaryConstantFolding(t *testing.T) {
 	expectPrintedNormalAndMangle(t, "x = -123 / 0", "x = -123 / 0;\n", "x = -Infinity;\n")
 	expectPrintedNormalAndMangle(t, "x = -123 / -0", "x = -123 / -0;\n", "x = Infinity;\n")
 
-	expectPrintedNormalAndMangle(t, "x = 3 < 6", "x = 3 < 6;\n", "x = 3 < 6;\n")
-	expectPrintedNormalAndMangle(t, "x = 3 > 6", "x = 3 > 6;\n", "x = 3 > 6;\n")
-	expectPrintedNormalAndMangle(t, "x = 3 <= 6", "x = 3 <= 6;\n", "x = 3 <= 6;\n")
-	expectPrintedNormalAndMangle(t, "x = 3 >= 6", "x = 3 >= 6;\n", "x = 3 >= 6;\n")
+	expectPrintedNormalAndMangle(t, "x = 3 < 6", "x = 3 < 6;\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = 3 > 6", "x = 3 > 6;\n", "x = false;\n")
+	expectPrintedNormalAndMangle(t, "x = 3 <= 6", "x = 3 <= 6;\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = 3 >= 6", "x = 3 >= 6;\n", "x = false;\n")
 	expectPrintedNormalAndMangle(t, "x = 3 == 6", "x = false;\n", "x = false;\n")
 	expectPrintedNormalAndMangle(t, "x = 3 != 6", "x = true;\n", "x = true;\n")
 	expectPrintedNormalAndMangle(t, "x = 3 === 6", "x = false;\n", "x = false;\n")
 	expectPrintedNormalAndMangle(t, "x = 3 !== 6", "x = true;\n", "x = true;\n")
 
+	expectPrintedNormalAndMangle(t, "x = 'a' < 'b'", "x = \"a\" < \"b\";\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = 'a' > 'b'", "x = \"a\" > \"b\";\n", "x = false;\n")
+	expectPrintedNormalAndMangle(t, "x = 'a' <= 'b'", "x = \"a\" <= \"b\";\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = 'a' >= 'b'", "x = \"a\" >= \"b\";\n", "x = false;\n")
+
+	expectPrintedNormalAndMangle(t, "x = 'ab' < 'abc'", "x = \"ab\" < \"abc\";\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = 'ab' > 'abc'", "x = \"ab\" > \"abc\";\n", "x = false;\n")
+	expectPrintedNormalAndMangle(t, "x = 'ab' <= 'abc'", "x = \"ab\" <= \"abc\";\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = 'ab' >= 'abc'", "x = \"ab\" >= \"abc\";\n", "x = false;\n")
+
+	// This checks for comparing by code point vs. by code unit
+	expectPrintedNormalAndMangle(t, "x = '𐙩' < 'ﬡ'", "x = \"𐙩\" < \"ﬡ\";\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = '𐙩' > 'ﬡ'", "x = \"𐙩\" > \"ﬡ\";\n", "x = false;\n")
+	expectPrintedNormalAndMangle(t, "x = '𐙩' <= 'ﬡ'", "x = \"𐙩\" <= \"ﬡ\";\n", "x = true;\n")
+	expectPrintedNormalAndMangle(t, "x = '𐙩' >= 'ﬡ'", "x = \"𐙩\" >= \"ﬡ\";\n", "x = false;\n")
+
 	expectPrintedNormalAndMangle(t, "x = 3 in 6", "x = 3 in 6;\n", "x = 3 in 6;\n")
 	expectPrintedNormalAndMangle(t, "x = 3 instanceof 6", "x = 3 instanceof 6;\n", "x = 3 instanceof 6;\n")
 	expectPrintedNormalAndMangle(t, "x = (3, 6)", "x = (3, 6);\n", "x = 6;\n")
