perf(compiler): reduce amount of generated code for safe accesses and nullish coalescing (#41563)

This is follow-up from #41437 and it reduces the amount of code we generate for safe property accesses (`a?.b`) and nullish coalescing (`a ?? b`) by:
1. Reusing variables in nested nullish coalescing expressions.
2. Not initializing temporary variables to `null`. The way our code is generated means that the value will always be overwritten before we compare against it so the initializer didn't really matter.

Fixes #41491.

PR Close #41563

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler/nullish_coalescing/nullish_coalescing_host_bindings.js

@@ -1,13 +1,12 @@
 hostBindings: function MyApp_HostBindings(rf, ctx) {
   if (rf & 1) {
     i0.ɵɵlistener("click", function MyApp_click_HostBindingHandler() {
-      let tmp_b_0 = null;
+      let $tmp$;
-      let tmp_b_1 = null;
+      return ctx.logLastName(($tmp$ = ($tmp$ = ctx.lastName) !== null && $tmp$ !== undefined ? $tmp$ : ctx.lastNameFallback) !== null && $tmp$ !== undefined ? $tmp$ : "unknown");
-      return ctx.logLastName((tmp_b_0 = (tmp_b_1 = ctx.lastName) !== null && tmp_b_1 !== undefined ? tmp_b_1 : ctx.lastNameFallback) !== null && tmp_b_0 !== undefined ? tmp_b_0 : "unknown");
     });
   }
   if (rf & 2) {
-    let tmp_b_0 = null;
+    let $tmp$;
-    i0.ɵɵattribute("first-name", "Hello, " + ((tmp_b_0 = ctx.firstName) !== null && tmp_b_0 !== undefined ? tmp_b_0 : "Frodo") + "!");
+    i0.ɵɵattribute("first-name", "Hello, " + (($tmp$ = ctx.firstName) !== null && $tmp$ !== undefined ? $tmp$ : "Frodo") + "!");
   }
 }

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler/nullish_coalescing/nullish_coalescing_interpolation_template.js

@@ -8,12 +8,11 @@ template: function MyApp_Template(rf, ctx) {
     i0.ɵɵelementEnd();
   }
   if (rf & 2) {
-    let tmp_0_0 = null;
+    let $tmp_0_0$;
-    let tmp_1_0 = null;
+    let $tmp_1_0$;
-    let tmp_1_1 = null;
     i0.ɵɵadvance(1);
-    i0.ɵɵtextInterpolate1("Hello, ", (tmp_0_0 = ctx.firstName) !== null && tmp_0_0 !== undefined ? tmp_0_0 : "Frodo", "!");
+    i0.ɵɵtextInterpolate1("Hello, ", ($tmp_0_0$ = ctx.firstName) !== null && $tmp_0_0$ !== undefined ? $tmp_0_0$ : "Frodo", "!");
     i0.ɵɵadvance(2);
-    i0.ɵɵtextInterpolate1("Your last name is ", (tmp_1_0 = (tmp_1_1 = ctx.lastName) !== null && tmp_1_1 !== undefined ? tmp_1_1 : ctx.lastNameFallback) !== null && tmp_1_0 !== undefined ? tmp_1_0 : "unknown", "");
+    i0.ɵɵtextInterpolate1("Your last name is ", ($tmp_1_0$ = ($tmp_1_0$ = ctx.lastName) !== null && $tmp_1_0$ !== undefined ? $tmp_1_0$ : ctx.lastNameFallback) !== null && $tmp_1_0$ !== undefined ? $tmp_1_0$ : "unknown", "");
   }
 }

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler/nullish_coalescing/nullish_coalescing_property_template.js

@@ -4,11 +4,10 @@ template: function MyApp_Template(rf, ctx) {
     i0.ɵɵelement(1, "span", 0);
   }
   if (rf & 2) {
-    let tmp_0_0 = null;
+    let $tmp_0_0$;
-    let tmp_1_0 = null;
+    let $tmp_1_0$;
-    let tmp_1_1 = null;
+    i0.ɵɵproperty("title", "Hello, " + (($tmp_0_0$ = ctx.firstName) !== null && $tmp_0_0$ !== undefined ? $tmp_0_0$ : "Frodo") + "!");
-    i0.ɵɵproperty("title", "Hello, " + ((tmp_0_0 = ctx.firstName) !== null && tmp_0_0 !== undefined ? tmp_0_0 : "Frodo") + "!");
     i0.ɵɵadvance(1);
-    i0.ɵɵproperty("title", (tmp_1_0 = (tmp_1_1 = "Your last name is " + ctx.lastName) !== null && tmp_1_1 !== undefined ? tmp_1_1 : ctx.lastNameFallback) !== null && tmp_1_0 !== undefined ? tmp_1_0 : "unknown");
+    i0.ɵɵproperty("title", ($tmp_1_0$ = ($tmp_1_0$ = "Your last name is " + ctx.lastName) !== null && $tmp_1_0$ !== undefined ? $tmp_1_0$ : ctx.lastNameFallback) !== null && $tmp_1_0$ !== undefined ? $tmp_1_0$ : "unknown");
   }
 }

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler_bindings/host_bindings/host_bindings_with_temporaries.js

@@ -5,7 +5,7 @@ HostBindingDir.ɵdir = /*@__PURE__*/ $r3$.ɵɵdefineDirective({
     hostVars: 1,
     hostBindings: function HostBindingDir_HostBindings(rf, ctx) {
       if (rf & 2) {
-        let $tmp0$ = null;
+        let $tmp0$;
         $r3$.ɵɵhostProperty("id", ($tmp0$ = ctx.getData()) == null ? null : $tmp0$.id);
       }
     }

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler_bindings/property_bindings/temporary_variables.js

@@ -1,7 +1,7 @@
 template: function MyComponent_Template(rf, ctx) {
   …
   if (rf & 2) {
-    let $tmp0$ = null;
+    let $tmp0$;
-    $r3$.ɵɵproperty("title", ctx.myTitle)("id", (tmp_1_0 = i0.ɵɵpipeBind1(1, 3, ctx.auth().identity())) == null ? null : tmp_1_0.id)("tabindex", 1);
+    $r3$.ɵɵproperty("title", ctx.myTitle)("id", ($tmp0$ = i0.ɵɵpipeBind1(1, 3, ctx.auth().identity())) == null ? null : $tmp0$.id)("tabindex", 1);
   }
 }

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler_i18n/element_attributes/interpolation_complex_expressions.js

@@ -14,7 +14,7 @@ template: function MyComponent_Template(rf, ctx) {
     $r3$.ɵɵelementEnd();
   }
   if (rf & 2) {
-    let $tmp_0_0$ = null;
+    let $tmp_0_0$;
     $r3$.ɵɵi18nExp(($tmp_0_0$ = ctx.valueA.getRawValue()) == null ? null : $tmp_0_0$.getTitle());
     $r3$.ɵɵi18nApply(1);
   }

packages/compiler-cli/test/compliance/test_cases/r3_view_compiler_i18n/nested_nodes/interpolation_complex_expressions.js

@@ -12,11 +12,11 @@ template: function MyComponent_Template(rf, ctx) {
     $r3$.ɵɵelementEnd();
   }
   if (rf & 2) {
-    let $tmp_2_0$ = null;
+    let $tmp_2_0$;
     $r3$.ɵɵadvance(2);
     $r3$.ɵɵi18nExp($r3$.ɵɵpipeBind1(2, 3, ctx.valueA))
                   (ctx.valueA == null ? null : ctx.valueA.a == null ? null : ctx.valueA.a.b)
                   (($tmp_2_0$ = ctx.valueA.getRawValue()) == null ? null : $tmp_2_0$.getTitle());
     $r3$.ɵɵi18nApply(1);
   }
-}
+}

packages/compiler/src/compiler_util/expression_converter.ts

@@ -259,8 +259,8 @@ function temporaryName(bindingId: string, temporaryNumber: number): string {
   return `tmp_${bindingId}_${temporaryNumber}`;
 }
 
-export function temporaryDeclaration(bindingId: string, temporaryNumber: number): o.Statement {
+function temporaryDeclaration(bindingId: string, temporaryNumber: number): o.Statement {
-  return new o.DeclareVarStmt(temporaryName(bindingId, temporaryNumber), o.NULL_EXPR);
+  return new o.DeclareVarStmt(temporaryName(bindingId, temporaryNumber));
 }
 
 function prependTemporaryDecls(
@@ -728,15 +728,13 @@ class _AstToIrVisitor implements cdAst.AstVisitor {
     }
 
     // Produce the conditional
-    return convertToStatementIfNeeded(mode, condition.conditional(o.literal(null), access));
+    return convertToStatementIfNeeded(mode, condition.conditional(o.NULL_EXPR, access));
   }
 
   private convertNullishCoalesce(ast: cdAst.Binary, mode: _Mode): any {
-    // Allocate the temporary variable before visiting the LHS and RHS, because they
-    // may allocate temporary variables too and we don't want them to be reused.
-    const temporary = this.allocateTemporary();
     const left: o.Expression = this._visit(ast.left, _Mode.Expression);
     const right: o.Expression = this._visit(ast.right, _Mode.Expression);
+    const temporary = this.allocateTemporary();
     this.releaseTemporary(temporary);
 
     // Generate the following expression. It is identical to how TS