tint/transform: Skip SimplifyPointers if possible

Change-Id: Id937d82e9062cf7a4c54401121ed6d22e5d4fd73
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/116870
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/transform/simplify_pointers.cc

@@ -130,48 +130,22 @@ struct SimplifyPointers::State {
         // A map of saved expressions to their saved variable name
         utils::Hashmap<const ast::Expression*, Symbol, 8> saved_vars;
 
-        // Register the ast::Expression transform handler.
+        bool needs_transform = false;
-        // This performs two different transformations:
-        // * Identifiers that resolve to the pointer-typed `let` declarations are
-        // replaced with the recursively inlined initializer expression for the
-        // `let` declaration.
-        // * Sub-expressions inside the pointer-typed `let` initializer expression
-        // that have been hoisted to a saved variable are replaced with the saved
-        // variable identifier.
-        ctx.ReplaceAll([&](const ast::Expression* expr) -> const ast::Expression* {
-            // Look to see if we need to swap this Expression with a saved variable.
-            if (auto saved_var = saved_vars.Find(expr)) {
-                return ctx.dst->Expr(*saved_var);
-            }
-
-            // Reduce the expression, folding away chains of address-of / indirections
-            auto op = Reduce(expr);
-
-            // Clone the reduced root expression
-            expr = ctx.CloneWithoutTransform(op.expr);
-
-            // And reapply the minimum number of address-of / indirections
-            for (int i = 0; i < op.indirections; i++) {
-                expr = ctx.dst->Deref(expr);
-            }
-            for (int i = 0; i > op.indirections; i--) {
-                expr = ctx.dst->AddressOf(expr);
-            }
-            return expr;
-        });
 
         // Find all the pointer-typed `let` declarations.
         // Note that these must be function-scoped, as module-scoped `let`s are not
         // permitted.
         for (auto* node : ctx.src->ASTNodes().Objects()) {
-            if (auto* let = node->As<ast::VariableDeclStatement>()) {
+            Switch(
+                node,  //
+                [&](const ast::VariableDeclStatement* let) {
                     if (!let->variable->Is<ast::Let>()) {
-                    continue;  // Not a `let` declaration. Ignore.
+                        return;  // Not a `let` declaration. Ignore.
                     }
 
                     auto* var = ctx.src->Sem().Get(let->variable);
                     if (!var->Type()->Is<type::Pointer>()) {
-                    continue;  // Not a pointer type. Ignore.
+                        return;  // Not a pointer type. Ignore.
                     }
 
                     // We're dealing with a pointer-typed `let` declaration.
@@ -185,7 +159,8 @@ struct SimplifyPointers::State {
                             // Create a new variable
                             auto saved_name = ctx.dst->Symbols().New(
                                 ctx.src->Symbols().NameFor(var->Declaration()->symbol) + "_save");
-                        auto* decl = ctx.dst->Decl(ctx.dst->Let(saved_name, ctx.Clone(idx_expr)));
+                            auto* decl =
+                                ctx.dst->Decl(ctx.dst->Let(saved_name, ctx.Clone(idx_expr)));
                             saved.Push(decl);
                             // Record the substitution of `idx_expr` to the saved variable
                             // with the symbol `saved_name`. This will be used by the
@@ -221,9 +196,50 @@ struct SimplifyPointers::State {
                     // As the original `let` declaration will be fully inlined, there's no
                     // need for the original declaration to exist. Remove it.
                     RemoveStatement(ctx, let);
+                },
+                [&](const ast::UnaryOpExpression* op) {
+                    if (op->op == ast::UnaryOp::kAddressOf) {
+                        // Transform can be skipped if no address-of operator is used, as there
+                        // will be no pointers that can be inlined.
+                        needs_transform = true;
                     }
+                });
         }
 
+        if (!needs_transform) {
+            return SkipTransform;
+        }
+
+        // Register the ast::Expression transform handler.
+        // This performs two different transformations:
+        // * Identifiers that resolve to the pointer-typed `let` declarations are
+        // replaced with the recursively inlined initializer expression for the
+        // `let` declaration.
+        // * Sub-expressions inside the pointer-typed `let` initializer expression
+        // that have been hoisted to a saved variable are replaced with the saved
+        // variable identifier.
+        ctx.ReplaceAll([&](const ast::Expression* expr) -> const ast::Expression* {
+            // Look to see if we need to swap this Expression with a saved variable.
+            if (auto saved_var = saved_vars.Find(expr)) {
+                return ctx.dst->Expr(*saved_var);
+            }
+
+            // Reduce the expression, folding away chains of address-of / indirections
+            auto op = Reduce(expr);
+
+            // Clone the reduced root expression
+            expr = ctx.CloneWithoutTransform(op.expr);
+
+            // And reapply the minimum number of address-of / indirections
+            for (int i = 0; i < op.indirections; i++) {
+                expr = ctx.dst->Deref(expr);
+            }
+            for (int i = 0; i > op.indirections; i--) {
+                expr = ctx.dst->AddressOf(expr);
+            }
+            return expr;
+        });
+
         ctx.Clone();
         return Program(std::move(b));
     }

src/tint/transform/simplify_pointers_test.cc

@@ -24,11 +24,18 @@ using SimplifyPointersTest = TransformTest;
 
 TEST_F(SimplifyPointersTest, EmptyModule) {
     auto* src = "";
-    auto* expect = "";
 
-    auto got = Run<Unshadow, SimplifyPointers>(src);
+    EXPECT_FALSE(ShouldRun<SimplifyPointers>(src));
+}
 
-    EXPECT_EQ(expect, str(got));
+TEST_F(SimplifyPointersTest, NoAddressOf) {
+    auto* src = R"(
+fn f(p : ptr<function, i32>) {
+  var v : i32;
+}
+)";
+
+    EXPECT_FALSE(ShouldRun<SimplifyPointers>(src));
 }
 
 TEST_F(SimplifyPointersTest, FoldPointer) {

test/tint/ptr_ref/load/param/workgroup/struct_in_array.wgsl.expected.dxc.hlsl

@@ -16,13 +16,13 @@ void main_inner(uint local_invocation_index) {
   {
     for(uint idx = local_invocation_index; (idx < 4u); idx = (idx + 1u)) {
       const uint i_1 = idx;
-      const str tint_symbol_2 = (str)0;
+      const str tint_symbol_3 = (str)0;
-      S[i_1] = tint_symbol_2;
+      S[i_1] = tint_symbol_3;
     }
   }
   GroupMemoryBarrierWithGroupSync();
-  const uint tint_symbol_3[1] = {2u};
+  const uint tint_symbol_2[1] = {2u};
-  const str r = func_S_X(tint_symbol_3);
+  const str r = func_S_X(tint_symbol_2);
 }
 
 [numthreads(1, 1, 1)]

test/tint/ptr_ref/load/param/workgroup/struct_in_array.wgsl.expected.fxc.hlsl

@@ -16,13 +16,13 @@ void main_inner(uint local_invocation_index) {
   {
     for(uint idx = local_invocation_index; (idx < 4u); idx = (idx + 1u)) {
       const uint i_1 = idx;
-      const str tint_symbol_2 = (str)0;
+      const str tint_symbol_3 = (str)0;
-      S[i_1] = tint_symbol_2;
+      S[i_1] = tint_symbol_3;
     }
   }
   GroupMemoryBarrierWithGroupSync();
-  const uint tint_symbol_3[1] = {2u};
+  const uint tint_symbol_2[1] = {2u};
-  const str r = func_S_X(tint_symbol_3);
+  const str r = func_S_X(tint_symbol_2);
 }
 
 [numthreads(1, 1, 1)]

test/tint/ptr_ref/store/param/workgroup/struct_in_array.wgsl.expected.dxc.hlsl

@@ -17,13 +17,13 @@ void main_inner(uint local_invocation_index) {
   {
     for(uint idx = local_invocation_index; (idx < 4u); idx = (idx + 1u)) {
       const uint i_1 = idx;
-      const str tint_symbol_3 = (str)0;
+      const str tint_symbol_4 = (str)0;
-      S[i_1] = tint_symbol_3;
+      S[i_1] = tint_symbol_4;
     }
   }
   GroupMemoryBarrierWithGroupSync();
-  const uint tint_symbol_4[1] = {2u};
+  const uint tint_symbol_3[1] = {2u};
-  func_S_X(tint_symbol_4);
+  func_S_X(tint_symbol_3);
 }
 
 [numthreads(1, 1, 1)]

test/tint/ptr_ref/store/param/workgroup/struct_in_array.wgsl.expected.fxc.hlsl

@@ -17,13 +17,13 @@ void main_inner(uint local_invocation_index) {
   {
     for(uint idx = local_invocation_index; (idx < 4u); idx = (idx + 1u)) {
       const uint i_1 = idx;
-      const str tint_symbol_3 = (str)0;
+      const str tint_symbol_4 = (str)0;
-      S[i_1] = tint_symbol_3;
+      S[i_1] = tint_symbol_4;
     }
   }
   GroupMemoryBarrierWithGroupSync();
-  const uint tint_symbol_4[1] = {2u};
+  const uint tint_symbol_3[1] = {2u};
-  func_S_X(tint_symbol_4);
+  func_S_X(tint_symbol_3);
 }
 
 [numthreads(1, 1, 1)]