Do not disable dynamic_mode for ThinLTO when invoked via LIPO options.

When using LLVM LIPO is automatically mapped to ThinLTO.
While for LIPO, fully dynamic linking needs to be off for correctness issues,
there is no such restriction for ThinLTO.

RELNOTES[NEW]: Do not disable fully dynamic linking with ThinLTO when invoked via LIPO options.

PiperOrigin-RevId: 162918429

1 files changed, 7 insertions, 4 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
index 784ab88a7b..13612763ce 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
@@ -359,7 +359,12 @@ public class CppConfiguration extends BuildConfiguration.Fragment {
       throw new AssertionError(e);
     }
 
-    if (cppOptions.getLipoMode() == LipoMode.BINARY) {
+    // Needs to be set before the first call to isLLVMCompiler().
+    this.toolchainIdentifier = toolchain.getToolchainIdentifier();
+
+    // With LLVM, ThinLTO is automatically used in place of LIPO. ThinLTO works fine with dynamic
+    // linking (and in fact creates a lot more work when dynamic linking is off).
+    if (cppOptions.getLipoMode() == LipoMode.BINARY && !isLLVMCompiler()) {
       // TODO(bazel-team): implement dynamic linking with LIPO
       this.dynamicMode = DynamicMode.OFF;
     } else {
@@ -380,8 +385,6 @@ public class CppConfiguration extends BuildConfiguration.Fragment {
 
     this.solibDirectory = "_solib_" + targetCpu;
 
-    this.toolchainIdentifier = toolchain.getToolchainIdentifier();
-
     this.supportsEmbeddedRuntimes = toolchain.getSupportsEmbeddedRuntimes();
     toolchain = addLegacyFeatures(toolchain);
     this.toolchainFeatures = new CcToolchainFeatures(toolchain);
@@ -1325,7 +1328,7 @@ public class CppConfiguration extends BuildConfiguration.Fragment {
     return cppOptions.isFdo();
   }
 
-  public boolean isLLVMCompiler() {
+  public final boolean isLLVMCompiler() {
     // TODO(tmsriram): Checking for "llvm" does not handle all the cases.  This
     // is temporary until the crosstool configuration is modified to add fields that
     // indicate which flavor of fdo is being used.