commit 52d718c11b73af6c5b278710dfce26434b2e0380
author Googler <noreply@google.com> Mon Sep 11 23:03:52 2017 +0200
committer Philipp Wollermann <philwo@google.com> Tue Sep 12 14:05:56 2017 +0200
tree a22d669abd37ba4aa74c21c5778e98fc41b7ae54
parent bb50580a7f3eb3f4e7c5fba8e92d20e931591a70

Don't attempt LTO indexing of cc_binary if there are no bitcode inputs to link.

The problem is that the linker will not produce the expected .params file output
if there are no inputs, and there is no need for this step in that case.
This required adding a method to check if there are any bitcode inputs to
the link either directly or indirectly via a library. This is the same walk done
by createLtoArtifacts once we decide to do an LTO indexing step.

RELNOTES: NONE
PiperOrigin-RevId: 168281516

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

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcBinary.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcBinary.java
index c613ff0..8c91d6b 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcBinary.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcBinary.java
@@ -288,7 +288,8 @@
     Iterable<LtoBackendArtifacts> ltoBackendArtifacts = ImmutableList.of();
     boolean usePic = CppHelper.usePic(ruleContext, !isLinkShared(ruleContext));
 
-    if (featureConfiguration.isEnabled(CppRuleClasses.THIN_LTO)) {
+    if (linkActionBuilder.hasLtoBitcodeInputs()
+        && featureConfiguration.isEnabled(CppRuleClasses.THIN_LTO)) {
       linkActionBuilder.setLtoIndexing(true);
       linkActionBuilder.setUsePicForLtoBackendActions(usePic);
       CppLinkAction indexAction = linkActionBuilder.build();

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

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppLinkActionBuilder.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppLinkActionBuilder.java
index d2a0317..d4f3e4e 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppLinkActionBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppLinkActionBuilder.java
@@ -498,6 +498,22 @@
     return uniqueLibrariesBuilder.build();
   }
 
+  /**
+   * Returns true if there are any LTO bitcode inputs to this link, either directly transitively via
+   * library inputs.
+   */
+  boolean hasLtoBitcodeInputs() {
+    if (!ltoBitcodeFiles.isEmpty()) {
+      return true;
+    }
+    for (LibraryToLink lib : libraries.build()) {
+      if (!lib.getLtoBitcodeFiles().isEmpty()) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private Iterable<LtoBackendArtifacts> createLtoArtifacts(
       PathFragment ltoOutputRootPrefix, NestedSet<LibraryToLink> uniqueLibraries) {
     Set<Artifact> compiled = new LinkedHashSet<>();