From 95d3ede664598916e6dced8a5e0f5003efd3c77a Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Thu, 20 Jun 2024 17:43:55 +0300
Subject: [PATCH] fix corner cases in `pure_getters` & `reduce_vars` (#5859)

fixes #5856
fixes #5857
fixes #5858
---
 lib/compress.js                  | 39 +++++++++++++++++++-------------
 test/compress/issue-5614.js      |  2 +-
 test/compress/optional-chains.js | 30 ++++++++++++++++++++++++
 test/compress/pure_getters.js    | 28 +++++++++++++++++++++++
 4 files changed, 82 insertions(+), 17 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index ff5652e4ba9..aaaf08b4714 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1261,8 +1261,9 @@ Compressor.prototype.compress = function(node) {
         });
         def(AST_Dot, function(tw, descend) {
             descend();
-            var expr = this.expression;
-            if (expr instanceof AST_SymbolRef) access(tw, expr.definition());
+            var node = this;
+            var expr = node.expression;
+            if (!node.optional && expr instanceof AST_SymbolRef) access(tw, expr.definition());
             return true;
         });
         def(AST_For, function(tw, descend, compressor) {
@@ -1362,15 +1363,18 @@ Compressor.prototype.compress = function(node) {
             pop_scope(tw, fn);
             return true;
         });
-        def(AST_Sub, function(tw) {
+        def(AST_Sub, function(tw, descend) {
             var node = this;
-            if (!node.optional) return;
             var expr = node.expression;
-            expr.walk(tw);
-            if (expr instanceof AST_SymbolRef) access(tw, expr.definition());
-            push(tw, true);
-            node.property.walk(tw);
-            pop(tw);
+            if (node.optional) {
+                expr.walk(tw);
+                push(tw, true);
+                node.property.walk(tw);
+                pop(tw);
+            } else {
+                descend();
+                if (expr instanceof AST_SymbolRef) access(tw, expr.definition());
+            }
             return true;
         });
         def(AST_Switch, function(tw, descend, compressor) {
@@ -8020,8 +8024,14 @@ Compressor.prototype.compress = function(node) {
                     prop.walk(tw);
                 });
                 if (node instanceof AST_Assign) {
-                    var right = get_rhs(node), shared = false;
-                    if (init && node.write_only === true && !right.has_side_effects(compressor)) {
+                    var fixed = sym.fixed_value();
+                    var right = get_rhs(node);
+                    var safe = fixed && fixed.is_constant();
+                    var shared = false;
+                    if (init
+                        && node.write_only === true
+                        && (safe || node.left === sym || right.equals(sym))
+                        && !right.has_side_effects(compressor)) {
                         initializations.add(node_def.id, right);
                     } else {
                         right.walk(tw);
@@ -8031,11 +8041,8 @@ Compressor.prototype.compress = function(node) {
                         if (!node.write_only || shared) {
                             verify_safe_usage(node_def, sym, value_modified[node_def.id]);
                         }
-                    } else {
-                        var fixed = sym.fixed_value();
-                        if (!fixed || !fixed.is_constant()) {
-                            verify_safe_usage(node_def, value_read[node_def.id], true);
-                        }
+                    } else if (!safe) {
+                        verify_safe_usage(node_def, value_read[node_def.id], true);
                     }
                 }
                 if (track_assigns(node_def, sym) && is_lhs(sym, node) !== sym) add_assigns(node_def, sym);
diff --git a/test/compress/issue-5614.js b/test/compress/issue-5614.js
index bdf6bfe17aa..27488731129 100644
--- a/test/compress/issue-5614.js
+++ b/test/compress/issue-5614.js
@@ -26,7 +26,7 @@ record_update: {
 currying: {
     options = {
         inline: true,
-        passes: 2,
+        passes: 3,
         pure_getters: "strict",
         reduce_funcs: true,
         reduce_vars: true,
diff --git a/test/compress/optional-chains.js b/test/compress/optional-chains.js
index fcff9a8a94d..4352bb66050 100644
--- a/test/compress/optional-chains.js
+++ b/test/compress/optional-chains.js
@@ -617,3 +617,33 @@ issue_5292_sub_pure_getters_strict: {
     ]
     node_version: ">=14"
 }
+
+issue_5856: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        try {
+            var a;
+            a?.p;
+            a.q;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            var a;
+            a?.p;
+            a.q;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=14"
+}
diff --git a/test/compress/pure_getters.js b/test/compress/pure_getters.js
index a06570c98e7..7f2ec4e8810 100644
--- a/test/compress/pure_getters.js
+++ b/test/compress/pure_getters.js
@@ -1687,3 +1687,31 @@ issue_4939: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5856: {
+    options = {
+        pure_getters: true,
+        reduce_vars: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = [ "FAIL", "PASS" ];
+        (function(b) {
+            var c = b[0];
+            b[0] = b[1];
+            b[1] = c;
+        })(a);
+        console.log(a[0]);
+    }
+    expect: {
+        var a = [ "FAIL", "PASS" ];
+        (function(b) {
+            var c = b[0];
+            b[0] = b[1];
+            b[1] = c;
+        })(a);
+        console.log(a[0]);
+    }
+    expect_stdout: "PASS"
+}