GCOV: Make the exit block placement from r223193 optional

By default we want our gcov emission to stay 4.2 compatible, which
means we need to continue emit the exit block last by default. We add
an option to emit it before the body for users that need it.

llvm-svn: 232438

3 files changed, 33 insertions, 14 deletions

diff --git a/llvm/include/llvm/Transforms/Instrumentation.h b/llvm/include/llvm/Transforms/Instrumentation.h
index 8fac6ca83ac..a1477930ed6 100644
--- a/llvm/include/llvm/Transforms/Instrumentation.h
+++ b/llvm/include/llvm/Transforms/Instrumentation.h
@@ -60,6 +60,10 @@ struct GCOVOptions {
   // Emit the name of the function in the .gcda files. This is redundant, as
   // the function identifier can be used to find the name from the .gcno file.
   bool FunctionNamesInData;
+
+  // Emit the exit block immediately after the start block, rather than after
+  // all of the function body's blocks.
+  bool ExitBlockBeforeBody;
 };
 ModulePass *createGCOVProfilerPass(const GCOVOptions &Options =
                                    GCOVOptions::getDefault());
diff --git a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
index e50ef1e0cd2..a793e69ce3d 100644
--- a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -47,6 +47,8 @@ using namespace llvm;
 static cl::opt<std::string>
 DefaultGCOVVersion("default-gcov-version", cl::init("402*"), cl::Hidden,
                    cl::ValueRequired);
+static cl::opt<bool> DefaultExitBlockBeforeBody("gcov-exit-block-before-body",
+                                                cl::init(false), cl::Hidden);
 
 GCOVOptions GCOVOptions::getDefault() {
   GCOVOptions Options;
@@ -55,6 +57,7 @@ GCOVOptions GCOVOptions::getDefault() {
   Options.UseCfgChecksum = false;
   Options.NoRedZone = false;
   Options.FunctionNamesInData = true;
+  Options.ExitBlockBeforeBody = DefaultExitBlockBeforeBody;
 
   if (DefaultGCOVVersion.size() != 4) {
     llvm::report_fatal_error(std::string("Invalid -default-gcov-version: ") +
@@ -307,7 +310,7 @@ namespace {
   class GCOVFunction : public GCOVRecord {
    public:
      GCOVFunction(DISubprogram SP, raw_ostream *os, uint32_t Ident,
-                  bool UseCfgChecksum)
+                  bool UseCfgChecksum, bool ExitBlockBeforeBody)
          : SP(SP), Ident(Ident), UseCfgChecksum(UseCfgChecksum), CfgChecksum(0),
            ReturnBlock(1, os) {
       this->os = os;
@@ -317,11 +320,13 @@ namespace {
 
       uint32_t i = 0;
       for (auto &BB : *F) {
-        // Skip index 1 (0, 2, 3, 4, ...) because that's assigned to the
-        // ReturnBlock.
-        bool first = i == 0;
-        Blocks.insert(std::make_pair(&BB, GCOVBlock(i++ + !first, os)));
+        // Skip index 1 if it's assigned to the ReturnBlock.
+        if (i == 1 && ExitBlockBeforeBody)
+          ++i;
+        Blocks.insert(std::make_pair(&BB, GCOVBlock(i++, os)));
       }
+      if (!ExitBlockBeforeBody)
+        ReturnBlock.Number = i;
 
       std::string FunctionNameAndLine;
       raw_string_ostream FNLOS(FunctionNameAndLine);
@@ -464,7 +469,7 @@ static bool functionHasLines(Function *F) {
       if (Loc.isUnknown()) continue;
 
       // Artificial lines such as calls to the global constructors.
-      if (Loc.getLine() == 0) continue; 
+      if (Loc.getLine() == 0) continue;
 
       return true;
     }
@@ -508,7 +513,8 @@ void GCOVProfiler::emitProfileNotes() {
       EntryBlock.splitBasicBlock(It);
 
       Funcs.push_back(make_unique<GCOVFunction>(SP, &out, FunctionIdent++,
-                                                Options.UseCfgChecksum));
+                                                Options.UseCfgChecksum,
+                                                Options.ExitBlockBeforeBody));
       GCOVFunction &Func = *Funcs.back();
 
       for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
diff --git a/llvm/test/Transforms/GCOVProfiling/return-block.ll b/llvm/test/Transforms/GCOVProfiling/return-block.ll
index 8954157f548..0fafc559f5d 100644
--- a/llvm/test/Transforms/GCOVProfiling/return-block.ll
+++ b/llvm/test/Transforms/GCOVProfiling/return-block.ll
@@ -1,8 +1,14 @@
 ; Inject metadata to set the .gcno file location
 ; RUN: echo '!19 = !{!"%/T/return-block.ll", !0}' > %t1
 ; RUN: cat %s %t1 > %t2
+
+; By default, the return block is last.
 ; RUN: opt -insert-gcov-profiling -disable-output %t2
-; RUN: llvm-cov gcov -n -dump %T/return-block.gcno 2>&1 | FileCheck %s
+; RUN: llvm-cov gcov -n -dump %T/return-block.gcno 2>&1 | FileCheck -check-prefix=CHECK -check-prefix=RETURN-LAST %s
+
+; But we can optionally emit it second, to match newer gcc versions.
+; RUN: opt -insert-gcov-profiling -gcov-exit-block-before-body -disable-output %t2
+; RUN: llvm-cov gcov -n -dump %T/return-block.gcno 2>&1 | FileCheck -check-prefix=CHECK -check-prefix=RETURN-SECOND %s
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
@@ -58,9 +64,12 @@ attributes #2 = { nounwind }
 !17 = distinct !MDLexicalBlock(line: 7, column: 7, file: !1, scope: !4)
 !18 = !MDLocation(line: 9, column: 1, scope: !4)
 
-; There should be no destination edges for block 1.
-; CHECK: Block : 0 Counter : 0
-; CHECK-NEXT:         Destination Edges : 2 (0), 
-; CHECK-NEXT: Block : 1 Counter : 0
-; CHECK-NEXT:         Source Edges : 4 (0), 
-; CHECK-NEXT: Block : 2 Counter : 0
+; There should be no destination edges for the exit block.
+; CHECK: Block : 1 Counter : 0
+; RETURN-LAST:       Destination Edges
+; RETURN-SECOND-NOT: Destination Edges
+; CHECK: Block : 2 Counter : 0
+; CHECK: Block : 4 Counter : 0
+; RETURN-LAST-NOT: Destination Edges
+; RETURN-SECOND:   Destination Edges
+; CHECK-NOT: Block :