[clang][codegen] Add a verifier IR pass before any further passes. (#68015)

This helps check clang generated good IR in the first place, as
otherwise this can cause UB in subsequent passes, with the final
verification pass not catching any issues.

This for example would have helped catch
#67937 earlier.

Author: mizvekov

clang/lib/CodeGen/BackendUtil.cpp

@@ -923,6 +923,9 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
 
   ModulePassManager MPM;
+  // Add a verifier pass, before any other passes, to catch CodeGen issues.
+  if (CodeGenOpts.VerifyModule)
+    MPM.addPass(VerifierPass());
 
   if (!CodeGenOpts.DisableLLVMPasses) {
     // Map our optimization levels into one of the distinct levels used to
@@ -1020,21 +1023,23 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
     }
 
     if (CodeGenOpts.FatLTO) {
-      MPM = PB.buildFatLTODefaultPipeline(Level, PrepareForThinLTO,
-                                          PrepareForThinLTO ||
-                                              shouldEmitRegularLTOSummary());
+      MPM.addPass(PB.buildFatLTODefaultPipeline(
+          Level, PrepareForThinLTO,
+          PrepareForThinLTO || shouldEmitRegularLTOSummary()));
     } else if (PrepareForThinLTO) {
-      MPM = PB.buildThinLTOPreLinkDefaultPipeline(Level);
+      MPM.addPass(PB.buildThinLTOPreLinkDefaultPipeline(Level));
     } else if (PrepareForLTO) {
-      MPM = PB.buildLTOPreLinkDefaultPipeline(Level);
+      MPM.addPass(PB.buildLTOPreLinkDefaultPipeline(Level));
     } else {
-      MPM = PB.buildPerModuleDefaultPipeline(Level);
+      MPM.addPass(PB.buildPerModuleDefaultPipeline(Level));
     }
   }
 
   // Add a verifier pass if requested. We don't have to do this if the action
   // requires code generation because there will already be a verifier pass in
   // the code-generation pipeline.
+  // Since we already added a verifier pass above, this
+  // might even not run the analysis, if previous passes caused no changes.
   if (!actionRequiresCodeGen(Action) && CodeGenOpts.VerifyModule)
     MPM.addPass(VerifierPass());
 

clang/test/CodeGen/code-coverage.c

@@ -15,10 +15,10 @@
 // RUN: %clang_cc1 -emit-llvm-bc -o /dev/null -fdebug-pass-manager -coverage-data-file=/dev/null %s 2>&1 | FileCheck --check-prefix=NEWPM %s
 // RUN: %clang_cc1 -emit-llvm-bc -o /dev/null -fdebug-pass-manager -coverage-data-file=/dev/null -O3 %s 2>&1 | FileCheck --check-prefix=NEWPM-O3 %s
 
-// NEWPM-NOT: Running pass
+// NEWPM: Running pass: VerifierPass
 // NEWPM: Running pass: GCOVProfilerPass
 
-// NEWPM-O3-NOT: Running pass
+// NEWPM-O3: Running pass: VerifierPass
 // NEWPM-O3: Running pass: Annotation2MetadataPass
 // NEWPM-O3: Running pass: ForceFunctionAttrsPass
 // NEWPM-O3: Running pass: GCOVProfilerPass

clang/test/CodeGen/lto-newpm-pipeline.c

@@ -25,7 +25,9 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm-bc -o /dev/null -mllvm -verify-analysis-invalidation=0 -fdebug-pass-manager -flto=thin -Oz %s 2>&1 | FileCheck %s \
 // RUN:   -check-prefix=CHECK-THIN-OPTIMIZED
 
-// CHECK-FULL-O0: Running pass: AlwaysInlinerPass
+// CHECK-FULL-O0: Running pass: VerifierPass
+// CHECK-FULL-O0-NEXT: Running analysis: VerifierAnalysis
+// CHECK-FULL-O0-NEXT: Running pass: AlwaysInlinerPass
 // CHECK-FULL-O0-NEXT: Running analysis: InnerAnalysisManagerProxy
 // CHECK-FULL-O0-NEXT: Running analysis: ProfileSummaryAnalysis
 // CHECK-FULL-O0-NEXT: Running pass: CoroConditionalWrapper
@@ -34,10 +36,11 @@
 // CHECK-FULL-O0-NEXT: Running pass: AnnotationRemarksPass
 // CHECK-FULL-O0-NEXT: Running analysis: TargetLibraryAnalysis
 // CHECK-FULL-O0-NEXT: Running pass: VerifierPass
-// CHECK-FULL-O0-NEXT: Running analysis: VerifierAnalysis
 // CHECK-FULL-O0-NEXT: Running pass: BitcodeWriterPass
 
-// CHECK-THIN-O0: Running pass: AlwaysInlinerPass
+// CHECK-THIN-O0: Running pass: VerifierPass
+// CHECK-THIN-O0-NEXT: Running analysis: VerifierAnalysis
+// CHECK-THIN-O0-NEXT: Running pass: AlwaysInlinerPass
 // CHECK-THIN-O0-NEXT: Running analysis: InnerAnalysisManagerProxy
 // CHECK-THIN-O0-NEXT: Running analysis: ProfileSummaryAnalysis
 // CHECK-THIN-O0-NEXT: Running pass: CoroConditionalWrapper
@@ -46,7 +49,6 @@
 // CHECK-THIN-O0-NEXT: Running pass: AnnotationRemarksPass
 // CHECK-THIN-O0-NEXT: Running analysis: TargetLibraryAnalysis
 // CHECK-THIN-O0-NEXT: Running pass: VerifierPass
-// CHECK-THIN-O0-NEXT: Running analysis: VerifierAnalysis
 // CHECK-THIN-O0-NEXT: Running pass: ThinLTOBitcodeWriterPass
 
 // TODO: The LTO pre-link pipeline currently invokes