Build support for passing a software cache prefetching hints file.

This flag assumes llvm supports an experimental 'prefetch-hints-flag' flag. The Bazel support simply plumbs the provided file through to the compiler.

The flag is independent from the other fdo_ flags, and may be applied in any combination with them.

RELNOTES: Introduce build support for providing cache prefetch hints.
PiperOrigin-RevId: 196916547

1 files changed, 12 insertions, 4 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/LtoBackendArtifacts.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/LtoBackendArtifacts.java
index df6dba73d0..f3e6d688a9 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/LtoBackendArtifacts.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/LtoBackendArtifacts.java
@@ -230,10 +230,18 @@ public final class LtoBackendArtifacts {
     // The input to the LTO backend step is the bitcode file.
     buildVariablesBuilder.addStringVariable(
         "thinlto_input_bitcode_file", bitcodeFile.getExecPath().toString());
-    Artifact autoFdoProfile = fdoSupport.getFdoSupport().buildProfileForLtoBackend(
-        fdoSupport, featureConfiguration, buildVariablesBuilder, ruleContext);
-    if (autoFdoProfile != null) {
-      builder.addInput(autoFdoProfile);
+    ProfileArtifacts profileArtifacts =
+        Preconditions.checkNotNull(
+            fdoSupport
+                .getFdoSupport()
+                .buildProfileForLtoBackend(
+                    fdoSupport, featureConfiguration, buildVariablesBuilder, ruleContext));
+
+    if (profileArtifacts.getProfileArtifact() != null) {
+      builder.addInput(profileArtifacts.getProfileArtifact());
+    }
+    if (profileArtifacts.getPrefetchHintsArtifact() != null) {
+      builder.addInput(profileArtifacts.getPrefetchHintsArtifact());
     }
 
     if (generateDwo) {