[browser][coreclr] Add profile-guided partial ReadyToRun

eng/restore/browserWasmMibcProfile.props

@@ -0,0 +1,10 @@
+<Project>
+  <PropertyGroup>
+    <BrowserWasmMibcPackageVersion>1.0.0-prerelease.26501.1</BrowserWasmMibcPackageVersion>
+    <BrowserWasmMibcProfile>$([MSBuild]::NormalizePath('$(NuGetPackageRoot)', 'optimization.browser-wasm.mibc.runtime', '$(BrowserWasmMibcPackageVersion)', 'data', 'DotNet_Blazor_Wasm.mibc'))</BrowserWasmMibcProfile>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageDownload Include="optimization.browser-wasm.MIBC.Runtime"
+                     Version="[$(BrowserWasmMibcPackageVersion)]" />
+  </ItemGroup>
+</Project>

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System.Runtime.InteropServices.JavaScript.Tests.csproj

@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+  <Import Condition="'$(RuntimeFlavor)' == 'CoreCLR'" Project="$(RepositoryEngineeringDir)restore\browserWasmMibcProfile.props" />
   <Import Condition="'$(TargetOS)' == 'browser'" Project="$(CommonTestPath)System/Net/Prerequisites/LocalEchoServer.props" />
 
   <PropertyGroup>
@@ -23,6 +24,8 @@
 
     <!-- Remove when PublishReadyToRun becomes default https://github.com/dotnet/runtime/issues/132466 -->
     <PublishReadyToRun Condition="'$(PublishReadyToRun)' == '' and '$(RuntimeFlavor)' == 'CoreCLR'">true</PublishReadyToRun>
+    <!-- Eager R2R profile: precompile only the profiled subset; the rest stays interpreted. -->
+    <WasmReadyToRunProfile Condition="'$(RuntimeFlavor)' == 'CoreCLR'">$(BrowserWasmMibcProfile)</WasmReadyToRunProfile>
   </PropertyGroup>
 
   <!-- Make debugging easier -->

src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets

@@ -25,8 +25,21 @@ Copyright (c) .NET Foundation. All rights reserved.
     <PublishReadyToRunComposite Condition="'$(PublishReadyToRunComposite)' == ''">false</PublishReadyToRunComposite>
     <!-- Compile every assembly into one shared (large) version bubble. -->
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--opt-cross-module:*</PublishReadyToRunCrossgen2ExtraArgs>
+    <!-- With a profile, compile only the profiled subset into the eager image (smaller startup); the rest
+         runs interpreted. Hardware intrinsics stay (ContainsMethodBody keeps them when the target has no
+         runtime codegen, i.e. wasm) and CoreLib JIT-helper implementations are rooted, so both remain
+         available before any interpreted call needs them. Without a profile the partial switch is omitted
+         and the full closure is compiled (unchanged behavior). -->
+    <PublishReadyToRunCrossgen2ExtraArgs Condition="'$(WasmReadyToRunProfile)' != ''">$(PublishReadyToRunCrossgen2ExtraArgs);--partial</PublishReadyToRunCrossgen2ExtraArgs>
   </PropertyGroup>
 
+  <!-- Optional external method profile (.mibc) that selects the eager partial subset. Flows into the base
+       SDK ReadyToRun PGO input, so crossgen2 receives it as -m:&lt;profile&gt;; combined with the partial
+       switch above it compiles just the profiled methods. Absent, the eager image is the full closure. -->
+  <ItemGroup Condition="'$(PublishReadyToRun)' == 'true' and '$(WasmReadyToRunProfile)' != ''">
+    <PublishReadyToRunPgoFiles Include="$(WasmReadyToRunProfile)" />
+  </ItemGroup>
+
   <!-- Prebuilt R2R probe directory for ConvertDllsToWebcil. PublishTrimmed is deliberately not consulted:
        publish always crossgens the whole closure, so framework and app R2R both come from obj/R2R. Only the
        dev-loop build differs - it never crossgens, so its BCL comes from the runtime pack's R2R images.
@@ -55,6 +68,8 @@ Copyright (c) .NET Foundation. All rights reserved.
   <Target Name="_WasmCoreClrValidateReadyToRun"
           Condition="'$(PublishReadyToRun)' == 'true'"
           BeforeTargets="_WasmCoreClrSelectR2RDirectories;_ResolveWasmOutputs">
+    <Error Condition="'$(WasmReadyToRunProfile)' != '' and !Exists('$(WasmReadyToRunProfile)')"
+           Text="WasmReadyToRunProfile '$(WasmReadyToRunProfile)' does not exist. Specify an existing .mibc file generated for the assemblies being published." />
     <Error Condition="'$(PublishReadyToRunComposite)' == 'true' and '$(_WasmEnableWebcil)' != 'true'"
            Text="PublishReadyToRunComposite for CoreCLR browser-wasm requires WebCIL-in-Wasm assemblies; enable WasmEnableWebcil." />
     <Error Condition="'$(PublishReadyToRunContainerFormat)' != 'wasm'"
@@ -230,11 +245,32 @@ Copyright (c) .NET Foundation. All rights reserved.
   <Target Name="_WasmCoreClrConservativeR2RInputs"
           Condition="'$(PublishReadyToRun)' == 'true'"
           BeforeTargets="_CreateR2RImages">
+    <PropertyGroup>
+      <_WasmReadyToRunState>Composite=$(PublishReadyToRunComposite)|Profile=$(WasmReadyToRunProfile)|ExtraArgs=$(PublishReadyToRunCrossgen2ExtraArgs)</_WasmReadyToRunState>
+      <_WasmReadyToRunStateHash>$([MSBuild]::StableStringHash('$(_WasmReadyToRunState)', 'Sha256'))</_WasmReadyToRunStateHash>
+      <_WasmReadyToRunStateDirectory>$([MSBuild]::NormalizeDirectory('$(IntermediateOutputPath)', 'R2R'))</_WasmReadyToRunStateDirectory>
+      <_WasmReadyToRunStateFile>$(_WasmReadyToRunStateDirectory)browser-r2r-state-$(_WasmReadyToRunStateHash).stamp</_WasmReadyToRunStateFile>
+      <_WasmReadyToRunStateChanged Condition="!Exists('$(_WasmReadyToRunStateFile)')">true</_WasmReadyToRunStateChanged>
+    </PropertyGroup>
+    <ItemGroup>
+      <_WasmObsoleteReadyToRunState Include="$(_WasmReadyToRunStateDirectory)browser-r2r-state-*.stamp"
+                                    Exclude="$(_WasmReadyToRunStateFile)" />
+    </ItemGroup>
+    <!-- Output timestamps can be newer than a newly written state file. Delete every batch output on a
+         state change so _CreateR2RImages cannot retain a mixture of full and partial images. -->
+    <Delete Condition="'$(_WasmReadyToRunStateChanged)' == 'true'"
+            Files="@(_ReadyToRunCompileList->'%(OutputR2RImage)');@(_ReadyToRunCompileList->'%(OutputPDBImage)')" />
+    <Delete Files="@(_WasmObsoleteReadyToRunState)" />
+    <WriteLinesToFile File="$(_WasmReadyToRunStateFile)"
+                      Lines="$(_WasmReadyToRunState)"
+                      Overwrite="true"
+                      WriteOnlyWhenDifferent="true" />
     <ItemGroup>
-      <_ReadyToRunCompilerInputs Include="@(_ReadyToRunCompileList);@(_ReadyToRunAssembliesToReference);@(_ReadyToRunCompositeBuildReferences);@(_ReadyToRunCompositeUnrootedBuildInput)" />
+      <_ReadyToRunCompilerInputs Include="$(_WasmReadyToRunStateFile);@(_ReadyToRunCompileList);@(_ReadyToRunAssembliesToReference);@(_ReadyToRunCompositeBuildReferences);@(_ReadyToRunCompositeUnrootedBuildInput)" />
       <!-- crossgen2 itself, not just the JIT: an updated compiler with an unchanged JIT must still invalidate. -->
       <_ReadyToRunCompilerInputs Include="$(_WasmResolvedCrossgen2Dir)crossgen2*;$(_WasmResolvedCrossgen2Dir)clrjit_universal_wasm_*"
                                  Condition="'$(_WasmResolvedCrossgen2Dir)' != ''" />
+      <FileWrites Include="$(_WasmReadyToRunStateFile)" />
     </ItemGroup>
     <!-- Crossgen2 configuration that isn't a file input: extra arguments (e.g. -p:PublishReadyToRunStripDebugInfo)
          and the composite mode, whose component stubs share the per-assembly <name>.wasm output names and would

src/mono/wasm/Wasm.Build.Tests/CoreCLRWasmNativeDefaultsTests.cs

@@ -26,6 +26,8 @@ public class CoreCLRWasmNativeDefaultsTests : WasmTemplateTestsBase
     {
         private static readonly Regex s_regex = new("\\*\\* WasmBuildNative:.*");
         private static readonly Regex s_r2rDirectoryRegex = new("\\*\\* WasmPublishR2RDir: '([^']*)'");
+        private static readonly Regex s_r2rExtraArgsRegex = new("\\*\\* R2RExtraArgs: '([^']*)'");
+        private static readonly Regex s_r2rPgoFilesRegex = new("\\*\\* R2RPgoFiles: '([^']*)'");
 
         public CoreCLRWasmNativeDefaultsTests(ITestOutputHelper output, SharedBuildPerTestClassFixture buildContext)
             : base(output, buildContext)
@@ -157,6 +159,88 @@ public void PublishReadyToRunDirectoryMatchesSdkOutputCasing()
             Assert.Equal(Path.Combine(GetObjDir(config), "R2R") + Path.DirectorySeparatorChar, match.Groups[1].Value);
         }
 
+        // The profile drives a crossgen2 --partial image: with a profile and R2R on, --partial is appended and
+        // the .mibc flows into PublishReadyToRunPgoFiles (crossgen2 -m:). With no profile the full closure is
+        // compiled (no --partial, no PGO input); the gate also requires PublishReadyToRun=true so a profile with
+        // R2R off is inert. Stops before crossgen2 - only the property/item wiring is under test; the crossgen2
+        // args just let the R2R restore resolve a compiler (in-build when BASE_DIR is set, SDK pack otherwise).
+        [Theory]
+        [InlineData(/*profileSet*/ true,  /*r2r*/ true,  /*expectPartial*/ true)]
+        [InlineData(/*profileSet*/ false, /*r2r*/ true,  /*expectPartial*/ false)]
+        [InlineData(/*profileSet*/ true,  /*r2r*/ false, /*expectPartial*/ false)]
+        public void WasmReadyToRunProfileControlsPartialAndPgoInput(bool profileSet, bool r2r, bool expectPartial)
+        {
+            Configuration config = Configuration.Release;
+            string profilePath = Path.Combine(BuildEnvironment.TestDataPath, "DotNet_Blazor_Wasm.mibc");
+            string printValueTarget = """
+                <Target Name="PrintR2RProfileFlow"
+                        DependsOnTargets="_WasmCoreClrSelectR2RDirectories">
+                    <Message Text="** R2RExtraArgs: '$(PublishReadyToRunCrossgen2ExtraArgs)'" Importance="High" />
+                    <Message Text="** R2RPgoFiles: '@(PublishReadyToRunPgoFiles)'" Importance="High" />
+                    <Error Text="Stopping after validating the R2R profile flow" />
+                </Target>
+                """;
+
+            string profileProperty = profileSet ? $"<WasmReadyToRunProfile>{profilePath}</WasmReadyToRunProfile>" : "";
+            ProjectInfo info = CopyTestAsset(
+                config,
+                aot: false,
+                TestAsset.WasmBasicTestApp,
+                $"coreclr_r2r_profile_{profileSet}_{r2r}",
+                extraProperties: $"<PublishReadyToRun>{r2r}</PublishReadyToRun>{profileProperty}",
+                insertAtEnd: printValueTarget);
+
+            (string _, string output) = BuildProject(
+                info,
+                config,
+                new BuildOptions(
+                    ExpectSuccess: false,
+                    ExtraMSBuildArgs: $"-t:PrintR2RProfileFlow {ReadyToRunTests.GetR2RBuildArgs(config)}"));
+
+            Assert.Contains("Stopping after validating the R2R profile flow", output);
+
+            Match extraArgs = s_r2rExtraArgsRegex.Match(output);
+            Match pgoFiles = s_r2rPgoFilesRegex.Match(output);
+            Assert.True(extraArgs.Success, output);
+            Assert.True(pgoFiles.Success, output);
+
+            if (expectPartial)
+            {
+                Assert.Contains("--partial", extraArgs.Groups[1].Value);
+                Assert.Contains(profilePath, pgoFiles.Groups[1].Value);
+            }
+            else
+            {
+                Assert.DoesNotContain("--partial", extraArgs.Groups[1].Value);
+                Assert.Equal("", pgoFiles.Groups[1].Value);
+            }
+        }
+
+        [Fact]
+        public void WasmReadyToRunProfileMustExist()
+        {
+            Configuration config = Configuration.Release;
+            const string profilePath = "missing-profile.mibc";
+            ProjectInfo info = CopyTestAsset(
+                config,
+                aot: false,
+                TestAsset.WasmBasicTestApp,
+                "coreclr_r2r_missing_profile",
+                extraProperties: $"""
+                    <PublishReadyToRun>true</PublishReadyToRun>
+                    <WasmReadyToRunProfile>{profilePath}</WasmReadyToRunProfile>
+                    """);
+
+            (string _, string output) = BuildProject(
+                info,
+                config,
+                new BuildOptions(
+                    ExpectSuccess: false,
+                    ExtraMSBuildArgs: ReadyToRunTests.GetR2RBuildArgs(config)));
+
+            Assert.Contains($"WasmReadyToRunProfile '{profilePath}' does not exist.", output);
+        }
+
         [Theory]
         [InlineData(false)]
         [InlineData(true)]

src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs

@@ -142,6 +142,78 @@ public void FrameworkAssembliesAreNotReadyToRunWhenDisabled(Configuration config
             AssertPerAppCrossgenRan(config, expected: false);
         }
 
+        // A WasmReadyToRunProfile drives a crossgen2 --partial image: only the profiled subset is precompiled,
+        // the rest is interpreted at runtime. Republish the same project through full, roots-only partial,
+        // profiled partial, and full states. This proves that the profile contributes methods, property-only
+        // changes invalidate incremental R2R output in both directions, and interpreter fallback covers methods
+        // left out of the eager image.
+        [ConditionalTheory(typeof(BuildTestBase), nameof(IsCoreClrRuntime))]
+        [InlineData(Configuration.Release)]
+        [TestCategory("no-workload")]
+        public async Task PublishPartialProfileRunsAllPages(Configuration config)
+        {
+            string profile = Path.Combine(BuildEnvironment.TestDataPath, "DotNet_Blazor_Wasm.mibc");
+            Assert.True(File.Exists(profile), $"Missing test profile '{profile}'.");
+            ProjectInfo info = CopyTestAsset(
+                config,
+                aot: false,
+                TestAsset.BlazorBasicTestApp,
+                "r2r_partial_profile",
+                extraProperties: """
+                    <PublishReadyToRun>true</PublishReadyToRun>
+                    <PublishTrimmed>false</PublishTrimmed>
+                    <PublishReadyToRunCrossgen2ExtraArgs Condition="'$(WasmBuildTestRootsOnlyPartial)' == 'true'">$(PublishReadyToRunCrossgen2ExtraArgs);--partial</PublishReadyToRunCrossgen2ExtraArgs>
+                    """);
+
+            string frameworkDir = PublishR2RClosure(info, config, extraArgs: "", label: "full");
+            AssertCoreLibReadyToRun(frameworkDir, expectReadyToRun: true);
+            string r2rDir = GetObjSubDir(config, "R2R");
+            long fullBytes = SumR2RTableBytes(r2rDir);
+            Assert.True(fullBytes > 0, "Full-closure publish produced no R2R tables.");
+
+            frameworkDir = PublishR2RClosure(
+                info,
+                config,
+                extraArgs: "-p:WasmBuildTestRootsOnlyPartial=true",
+                label: "roots-only");
+            long rootsOnlyBytes = SumR2RTableBytes(r2rDir);
+            Assert.True(rootsOnlyBytes > 0, "Roots-only partial image produced no R2R tables.");
+            Assert.NotEqual(fullBytes, rootsOnlyBytes);
+
+            frameworkDir = PublishR2RClosure(
+                info,
+                config,
+                extraArgs: $"-p:WasmReadyToRunProfile=\"{profile}\"",
+                label: "profiled");
+            AssertCoreLibReadyToRun(frameworkDir, expectReadyToRun: true);
+            AssertPerAppCrossgenRan(config, expected: true);
+
+            long profiledBytes = SumR2RTableBytes(r2rDir);
+            Assert.NotEqual(rootsOnlyBytes, profiledBytes);
+            Assert.NotEqual(fullBytes, profiledBytes);
+
+            await RunForPublishWithWebServer(new BlazorRunOptions(config,
+                CheckCounter: false,
+                ExecuteAfterLoaded: (_, page) => InteractAllPagesAsync(page)));
+
+            PublishR2RClosure(info, config, extraArgs: "", label: "full-restored");
+            long restoredFullBytes = SumR2RTableBytes(r2rDir);
+            Assert.Equal(fullBytes, restoredFullBytes);
+        }
+
+        private string PublishR2RClosure(ProjectInfo info, Configuration config, string extraArgs, string label)
+        {
+            string r2rArgs = $"{GetR2RBuildArgs(config)} {extraArgs}";
+            BlazorPublish(
+                info,
+                config,
+                new PublishOptions(
+                    UseCache: false,
+                    Label: label,
+                    ExtraMSBuildArgs: r2rArgs));
+            return GetBlazorBinFrameworkDir(config, forPublish: true);
+        }
+
         [ConditionalTheory(typeof(BuildTestBase), nameof(IsCoreClrRuntime))]
         [InlineData(Configuration.Release)]
         [TestCategory("no-workload")]
@@ -151,7 +223,6 @@ public void CompositeRequiresWebcil(Configuration config)
                 extraProperties: "<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>true</PublishReadyToRunComposite><WasmEnableWebcil>false</WasmEnableWebcil>");
             (string _, string output) = BlazorPublish(info, config,
                 new PublishOptions(ExpectSuccess: false, ExtraMSBuildArgs: GetR2RBuildArgs(config, composite: true)));
-
             Assert.Contains("PublishReadyToRunComposite for CoreCLR browser-wasm requires WebCIL-in-Wasm assemblies", output);
         }
 
@@ -271,7 +342,7 @@ private void AssertPerAppCrossgenRan(Configuration config, bool expected)
         // crossgen2 itself from the SDK pack (the SDK restores it when PublishReadyToRun is set), so passing a
         // non-existent Crossgen2InBuildDir there would break the call-helpers generator. All inert if BASE_DIR is unset.
         // TODO-WASM https://github.com/dotnet/runtime/issues/135023: drop the composite-only shim once the SDK names wasm R2R outputs.
-        private static string GetR2RBuildArgs(Configuration config, bool composite)
+        internal static string GetR2RBuildArgs(Configuration config, bool composite = false)
         {
             string? baseDir = EnvironmentVariables.BaseDir;
             if (string.IsNullOrEmpty(baseDir))
@@ -293,6 +364,20 @@ private static string GetR2RBuildArgs(Configuration config, bool composite)
             return string.Join(" ", args);
         }
 
+        // Total table bytes across the canonical per-app R2R outputs. The base SDK names them .dll while the
+        // wasm-aware task shim names them .wasm. Measuring the fingerprinted publish directory would count
+        // files retained from earlier incremental publishes.
+        private static long SumR2RTableBytes(string r2rDir)
+        {
+            long total = 0;
+            foreach (string image in Directory.EnumerateFiles(r2rDir)
+                .Where(path => Path.GetExtension(path) is ".dll" or ".wasm"))
+            {
+                total += GetReadyToRunTableSize(image);
+            }
+            return total;
+        }
+
         private static int GetReadyToRunTableSize(string webcilPath)
         {
             using FileStream stream = File.OpenRead(webcilPath);

src/mono/wasm/Wasm.Build.Tests/Wasm.Build.Tests.csproj

@@ -1,4 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Condition="'$(RuntimeFlavor)' == 'CoreCLR'" Project="$(RepositoryEngineeringDir)restore\browserWasmMibcProfile.props" />
   <PropertyGroup>
     <TargetFramework>$(NetCoreAppToolCurrent)</TargetFramework>
     <SkipXunitTrimmerDescriptor>true</SkipXunitTrimmerDescriptor>
@@ -69,6 +70,10 @@
     <None Include="$(BrowserProjectRoot)\test-main.mjs" CopyToOutputDirectory="PreserveNewest" />
     <None Include="..\testassets\**\*" Link="testassets\%(RecursiveDir)%(FileName)%(Extension)" CopyToOutputDirectory="PreserveNewest" />
     <None Include="data\**\*" Link="data\%(RecursiveDir)%(FileName)%(Extension)" CopyToOutputDirectory="PreserveNewest" />
+    <None Include="$(BrowserWasmMibcProfile)"
+          Condition="'$(BrowserWasmMibcProfile)' != ''"
+          Link="data\DotNet_Blazor_Wasm.mibc"
+          CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
 
   <!-- Deploy dotnet-pgo (and its managed dependencies) into a dotnet-pgo/ subfolder next to the test so