Use Blaze's CommandLine infrastructure to expand ThinLTO command line…

…s only when necessary to avoid unnecessary memory consumption

RELNOTES: None.
PiperOrigin-RevId: 251819397

src/main/java/com/google/devtools/build/lib/rules/cpp/LtoBackendArtifacts.java

@@ -17,6 +17,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.actions.CommandLine;
 import com.google.devtools.build.lib.analysis.actions.ActionConstructionContext;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.config.BuildOptions;
@@ -29,7 +30,6 @@
 import com.google.devtools.build.lib.rules.cpp.CppLinkAction.LinkArtifactFactory;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.PathFragment;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import javax.annotation.Nullable;
@@ -289,18 +289,9 @@ private void scheduleLtoBackendAction(
       builder.setExecutable(compiler);
     }
 
-    List<String> execArgs = new ArrayList<>();
-    execArgs.addAll(
-        CppHelper.getCommandLine(
-            ruleErrorConsumer, featureConfiguration, buildVariables, CppActionNames.LTO_BACKEND));
-    // If this is a PIC compile (set based on the CppConfiguration), the PIC
-    // option should be added after the rest of the command line so that it
-    // cannot be overridden. This is consistent with the ordering in the
-    // CppCompileAction's compiler options.
-    if (usePic) {
-      execArgs.add("-fPIC");
-    }
-    builder.addExecutableArguments(execArgs);
+    CommandLine ltoCommandLine =
+        new LtoBackendCommandLine(featureConfiguration, buildVariables, usePic);
+    builder.addCommandLine(ltoCommandLine);
 
     actionConstructionContext.registerAction(builder.build(actionConstructionContext));
   }

src/main/java/com/google/devtools/build/lib/rules/cpp/LtoBackendCommandLine.java

@@ -0,0 +1,60 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.rules.cpp;
+
+import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.actions.CommandLine;
+import com.google.devtools.build.lib.actions.CommandLineExpansionException;
+import com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures.ExpansionException;
+import com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures.FeatureConfiguration;
+
+/**
+ * A representation of command line for {@link LtoBackendAction}.
+ *
+ * <p>We have this class so we're able to defer construction of the command line to execution phase.
+ */
+public class LtoBackendCommandLine extends CommandLine {
+
+  private final FeatureConfiguration featureConfiguration;
+  private final CcToolchainVariables buildVariables;
+  private final boolean usePic;
+
+  LtoBackendCommandLine(
+      FeatureConfiguration featureConfiguration,
+      CcToolchainVariables ccToolchainVariables,
+      boolean usePic) {
+    this.featureConfiguration = featureConfiguration;
+    this.buildVariables = ccToolchainVariables;
+    this.usePic = usePic;
+  }
+
+  @Override
+  public Iterable<String> arguments() throws CommandLineExpansionException {
+    ImmutableList.Builder<String> args = ImmutableList.builder();
+    try {
+      args.addAll(featureConfiguration.getCommandLine(CppActionNames.LTO_BACKEND, buildVariables));
+    } catch (ExpansionException e) {
+      throw new CommandLineExpansionException(e.getMessage());
+    }
+    // If this is a PIC compile (set based on the CppConfiguration), the PIC
+    // option should be added after the rest of the command line so that it
+    // cannot be overridden. This is consistent with the ordering in the
+    // CppCompileAction's compiler options.
+    if (usePic) {
+      args.add("-fPIC");
+    }
+    return args.build();
+  }
+}