[Clang] Enable -print-pipeline-passes in clang.

Reviewed By: arsenm, aeubanks

Differential Revision: https://reviews.llvm.org/D127221

clang/lib/CodeGen/BackendUtil.cpp

@@ -91,6 +91,7 @@ using namespace llvm;
 
 namespace llvm {
 extern cl::opt<bool> DebugInfoCorrelate;
+extern cl::opt<bool> PrintPipelinePasses;
 
 // Experiment to move sanitizers earlier.
 static cl::opt<bool> ClSanitizeOnOptimizerEarlyEP(
@@ -1090,6 +1091,17 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
       TheModule->addModuleFlag(Module::Error, "UnifiedLTO", uint32_t(1));
   }
 
+  // Print a textual, '-passes=' compatible, representation of pipeline if
+  // requested.
+  if (PrintPipelinePasses) {
+    MPM.printPipeline(outs(), [&PIC](StringRef ClassName) {
+      auto PassName = PIC.getPassNameForClassName(ClassName);
+      return PassName.empty() ? ClassName : PassName;
+    });
+    outs() << "\n";
+    return;
+  }
+
   // Now that we have all of the passes ready, run them.
   {
     PrettyStackTraceString CrashInfo("Optimizer");
@@ -1127,6 +1139,13 @@ void EmitAssemblyHelper::RunCodegenPipeline(
     return;
   }
 
+  // If -print-pipeline-passes is requested, don't run the legacy pass manager.
+  // FIXME: when codegen is switched to use the new pass manager, it should also
+  // emit pass names here.
+  if (PrintPipelinePasses) {
+    return;
+  }
+
   {
     PrettyStackTraceString CrashInfo("Code generation");
     llvm::TimeTraceScope TimeScope("CodeGenPasses");

clang/test/CodeGen/print-pipeline-passes.c

@@ -0,0 +1,9 @@
+// Test that -print-pipeline-passes works in Clang
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm-bc -o /dev/null -mllvm -print-pipeline-passes -O0 %s 2>&1 | FileCheck %s
+
+// Don't try to check all passes, just a few to make sure that something is
+// actually printed.
+// CHECK: always-inline
+// CHECK-SAME: annotation-remarks
+void Foo(void) {}