D3D: Fall back to old compiler DLL.

BUILD.gn

@@ -153,12 +153,23 @@ config("build_id_config") {
 # Windows ARM64 is available since 10.0.16299 so no need to copy
 # d3dcompiler_47.dll because this file is available as inbox.
 if (is_win && target_cpu != "arm64") {
+  # We also ship an older DLL for compatiblity with Windows 7 machines without
+  # the UCRT. This DLL isn't available in the standard SDK distribution.
+  _old_compiler = "$windows_sdk_path/Redist/D3D/$target_cpu/d3dcompiler_old.dll"
+  _has_old_compiler =
+      exec_script("scripts/file_exists.py", [ _old_compiler ], "value")
+
   copy("copy_compiler_dll") {
     sources = [
       "$windows_sdk_path/Redist/D3D/$target_cpu/d3dcompiler_47.dll",
     ]
+
+    if (_has_old_compiler) {
+      sources += [ _old_compiler ]
+    }
+
     outputs = [
-      "$root_out_dir/d3dcompiler_47.dll",
+      "$root_out_dir/{{source_file_part}}",
     ]
   }
 }

scripts/file_exists.py

+#!/usr/bin/python2
+# Copyright 2019 The ANGLE Project Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# Simple helper for use in 'gn' files to check if a file exists.
+
+import os, shutil, sys
+
+def main():
+	if len(sys.argv) != 2:
+		print "Usage: %s <path>" % sys.argv[0]
+		sys.exit(1)
+
+	if os.path.exists(sys.argv[1]):
+		print "true"
+	else:
+		print "false"
+	sys.exit(0)
+
+if __name__ == '__main__':
+  main()

src/libANGLE/renderer/d3d/HLSLCompiler.cpp

@@ -16,9 +16,9 @@
 #include "libANGLE/renderer/d3d/ContextD3D.h"
 #include "third_party/trace_event/trace_event.h"
 
-#if ANGLE_APPEND_ASSEMBLY_TO_SHADER_DEBUG_INFO == ANGLE_ENABLED
 namespace
 {
+#if ANGLE_APPEND_ASSEMBLY_TO_SHADER_DEBUG_INFO == ANGLE_ENABLED
 #    ifdef CREATE_COMPILER_FLAG_INFO
 #        undef CREATE_COMPILER_FLAG_INFO
 #    endif
@@ -81,9 +81,19 @@ bool IsCompilerFlagSet(UINT mask, UINT flag)
             return isFlagSet;
     }
 }
-}  // anonymous namespace
 #endif  // ANGLE_APPEND_ASSEMBLY_TO_SHADER_DEBUG_INFO == ANGLE_ENABLED
 
+constexpr char kOldCompilerLibrary[] = "d3dcompiler_old.dll";
+
+enum D3DCompilerLoadLibraryResult
+{
+    D3DCompilerDefaultLibrarySuccess,
+    D3DCompilerOldLibrarySuccess,
+    D3DCompilerFailure,
+    D3DCompilerEnumBoundary,
+};
+}  // anonymous namespace
+
 namespace rx
 {
 
@@ -132,15 +142,31 @@ angle::Result HLSLCompiler::ensureInitialized(d3d::Context *context)
         // built with.
         mD3DCompilerModule = LoadLibraryA(D3DCOMPILER_DLL_A);
 
-        if (!mD3DCompilerModule)
+        if (mD3DCompilerModule)
         {
-            DWORD lastError = GetLastError();
-            ERR() << "LoadLibrary(" << D3DCOMPILER_DLL_A << ") failed. GetLastError=" << lastError;
-            ANGLE_TRY_HR(context, E_OUTOFMEMORY, "LoadLibrary failed to load D3D Compiler DLL.");
+            ANGLE_HISTOGRAM_ENUMERATION("GPU.ANGLE.D3DCompilerLoadLibraryResult",
+                                        D3DCompilerDefaultLibrarySuccess, D3DCompilerEnumBoundary);
+        }
+        else
+        {
+            WARN() << "Failed to load HLSL compiler library. Trying old DLL.";
+            mD3DCompilerModule = LoadLibraryA(kOldCompilerLibrary);
+            if (mD3DCompilerModule)
+            {
+                ANGLE_HISTOGRAM_ENUMERATION("GPU.ANGLE.D3DCompilerLoadLibraryResult",
+                                            D3DCompilerOldLibrarySuccess, D3DCompilerEnumBoundary);
+            }
         }
     }
 
-    ASSERT(mD3DCompilerModule);
+    if (!mD3DCompilerModule)
+    {
+        DWORD lastError = GetLastError();
+        ERR() << "LoadLibrary(" << D3DCOMPILER_DLL_A << ") failed. GetLastError=" << lastError;
+        ANGLE_HISTOGRAM_ENUMERATION("GPU.ANGLE.D3DCompilerLoadLibraryResult", D3DCompilerFailure,
+                                    D3DCompilerEnumBoundary);
+        ANGLE_TRY_HR(context, E_OUTOFMEMORY, "LoadLibrary failed to load D3D Compiler DLL.");
+    }
 
     mD3DCompileFunc =
         reinterpret_cast<pD3DCompile>(GetProcAddress(mD3DCompilerModule, "D3DCompile"));