r314002 - [Coverage] Add an option to emit limited coverage info

[Vedant Kumar via cfe-commits]

Author: vedantk
Date: Fri Sep 22 11:23:04 2017
New Revision: 314002

URL: http://llvm.org/viewvc/llvm-project?rev=314002&view=rev
Log:
[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

Modified:
    cfe/trunk/lib/CodeGen/CodeGenModule.cpp
    cfe/trunk/test/CoverageMapping/header.cpp

Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=314002&r1=314001&r2=314002&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Fri Sep 22 11:23:04 2017
@@ -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::AddDeferredUnusedCov
   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;

Modified: cfe/trunk/test/CoverageMapping/header.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CoverageMapping/header.cpp?rev=314002&r1=314001&r2=314002&view=diff
==============================================================================
--- cfe/trunk/test/CoverageMapping/header.cpp (original)
+++ cfe/trunk/test/CoverageMapping/header.cpp Fri Sep 22 11:23:04 2017
@@ -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