[Coverage] Add an option to emit limited coverage info

Add an option to emit limited coverage info for unused decls. It's just a
cl::opt for now to allow us to experiment quickly.

When building llc, this results in an 84% size reduction in the llvm_covmap
section, and a similar size reduction in the llvm_prf_names section. In
practice I expect the size reduction to be roughly quadratic with the size of
the program.

The downside is that coverage for headers will no longer be complete. This will
make the line/function/region coverage metrics incorrect, since they will be
artificially high. One mitigation would be to somehow disable those metrics
when using limited-coverage=true.

This is related to: llvm.org/PR34533 (make SourceBasedCodeCoverage scale)

Differential Revision: https://reviews.llvm.org/D38107

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@314002 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 43607002544e3d577e009e770477849fb9108091..4903d408ada6f97ad7a747f1e45abad2b799c491 100644 (file)
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -61,6 +61,11 @@
 using namespace clang;
 using namespace CodeGen;
 
+static llvm::cl::opt<bool> LimitedCoverage(
+    "limited-coverage-experimental", llvm::cl::ZeroOrMore,
+    llvm::cl::desc("Emit limited coverage mapping information (experimental)"),
+    llvm::cl::init(false));
+
 static const char AnnotationSection[] = "llvm.metadata";
 
 static CGCXXABI *createCXXABI(CodeGenModule &CGM) {
@@ -4231,6 +4236,9 @@ void CodeGenModule::AddDeferredUnusedCoverageMapping(Decl *D) {
   case Decl::CXXDestructor: {
     if (!cast<FunctionDecl>(D)->doesThisDeclarationHaveABody())
       return;
+    SourceManager &SM = getContext().getSourceManager();
+    if (LimitedCoverage && SM.getMainFileID() != SM.getFileID(D->getLocStart()))
+      return;
     auto I = DeferredEmptyCoverageMappingDecls.find(D);
     if (I == DeferredEmptyCoverageMappingDecls.end())
       DeferredEmptyCoverageMappingDecls[D] = true;

diff --git a/test/CoverageMapping/header.cpp b/test/CoverageMapping/header.cpp
index 5e0b3111c1d373b2afab9ee9d6590131afa4696b..d42c154446643f3c96fe9ad584ca7c648458b4a1 100644 (file)
--- a/test/CoverageMapping/header.cpp
+++ b/test/CoverageMapping/header.cpp
@@ -2,6 +2,9 @@
 // RUN: FileCheck -input-file %tmapping %s --check-prefix=CHECK-FUNC
 // RUN: FileCheck -input-file %tmapping %s --check-prefix=CHECK-STATIC-FUNC
 // RUN: FileCheck -input-file %tmapping %s --check-prefix=CHECK-STATIC-FUNC2
+//
+// RUN: %clang_cc1 -fprofile-instrument=clang -fcoverage-mapping -mllvm -limited-coverage-experimental=true -dump-coverage-mapping -emit-llvm-only -main-file-name header.cpp %s > %tmapping.limited
+// RUN: FileCheck -input-file %tmapping.limited %s --check-prefix=CHECK-LIMITED
 
 #include "Inputs/header1.h"
 
@@ -22,3 +25,5 @@ int main() {
 
 // CHECK-STATIC-FUNC2: static_func2
 // CHECK-STATIC-FUNC2: File 0, 21:33 -> 29:2 = 0
+
+// CHECK-LIMITED-NOT: static_func2