[Inliner] Report when inlining fails because callee's def is unavailable

Summary:
This is obviously an interesting case because it may motivate code
restructuring or LTO.

Reporting this requires instantiation of ORE in the loop where the call
sites are first gathered.  I've checked compile-time
overhead *with* -Rpass-with-hotness and the worst slow-down was 6% in
mcf and quickly tailing off.  As before without -Rpass-with-hotness
there is no overhead.

Because this could be a pretty noisy diagnostics, it is currently
qualified as 'verbose'.  As of this patch, 'verbose' diagnostics are
only emitted with -Rpass-with-hotness, i.e. when the output is expected
to be filtered.

Reviewers: eraman, chandlerc, davidxl, hfinkel

Subscribers: tejohnson, Prazek, davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D23415

llvm-svn: 279860

2 files changed, 24 insertions, 12 deletions

diff --git a/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp b/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp
index e150d9d2d82..09a4ce51472 100644
--- a/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp
+++ b/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp
@@ -68,29 +68,32 @@ void OptimizationRemarkEmitter::emitOptimizationRemark(const char *PassName,
 
 void OptimizationRemarkEmitter::emitOptimizationRemarkMissed(
     const char *PassName, const DebugLoc &DLoc, const Value *V,
-    const Twine &Msg) {
+    const Twine &Msg, bool IsVerbose) {
   LLVMContext &Ctx = F->getContext();
-  Ctx.diagnose(DiagnosticInfoOptimizationRemarkMissed(PassName, *F, DLoc, Msg,
-                                                      computeHotness(V)));
+  if (!IsVerbose || shouldEmitVerbose())
+    Ctx.diagnose(DiagnosticInfoOptimizationRemarkMissed(PassName, *F, DLoc, Msg,
+                                                        computeHotness(V)));
 }
 
 void OptimizationRemarkEmitter::emitOptimizationRemarkMissed(
-    const char *PassName, Loop *L, const Twine &Msg) {
-  emitOptimizationRemarkMissed(PassName, L->getStartLoc(), L->getHeader(), Msg);
+    const char *PassName, Loop *L, const Twine &Msg, bool IsVerbose) {
+  emitOptimizationRemarkMissed(PassName, L->getStartLoc(), L->getHeader(), Msg,
+                               IsVerbose);
 }
 
 void OptimizationRemarkEmitter::emitOptimizationRemarkAnalysis(
     const char *PassName, const DebugLoc &DLoc, const Value *V,
-    const Twine &Msg) {
+    const Twine &Msg, bool IsVerbose) {
   LLVMContext &Ctx = F->getContext();
-  Ctx.diagnose(DiagnosticInfoOptimizationRemarkAnalysis(PassName, *F, DLoc, Msg,
-                                                        computeHotness(V)));
+  if (!IsVerbose || shouldEmitVerbose())
+    Ctx.diagnose(DiagnosticInfoOptimizationRemarkAnalysis(
+        PassName, *F, DLoc, Msg, computeHotness(V)));
 }
 
 void OptimizationRemarkEmitter::emitOptimizationRemarkAnalysis(
-    const char *PassName, Loop *L, const Twine &Msg) {
+    const char *PassName, Loop *L, const Twine &Msg, bool IsVerbose) {
   emitOptimizationRemarkAnalysis(PassName, L->getStartLoc(), L->getHeader(),
-                                 Msg);
+                                 Msg, IsVerbose);
 }
 
 void OptimizationRemarkEmitter::emitOptimizationRemarkAnalysisFPCommute(
diff --git a/llvm/lib/Transforms/IPO/Inliner.cpp b/llvm/lib/Transforms/IPO/Inliner.cpp
index 86781b3fe33..befadb63db5 100644
--- a/llvm/lib/Transforms/IPO/Inliner.cpp
+++ b/llvm/lib/Transforms/IPO/Inliner.cpp
@@ -452,9 +452,10 @@ inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG,
 
   for (CallGraphNode *Node : SCC) {
     Function *F = Node->getFunction();
-    if (!F)
+    if (!F || F->isDeclaration())
       continue;
 
+    OptimizationRemarkEmitter ORE(F);
     for (BasicBlock &BB : *F)
       for (Instruction &I : BB) {
         CallSite CS(cast<Value>(&I));
@@ -467,8 +468,16 @@ inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG,
         // it.  If it is an indirect call, inlining may resolve it to be a
         // direct call, so we keep it.
         if (Function *Callee = CS.getCalledFunction())
-          if (Callee->isDeclaration())
+          if (Callee->isDeclaration()) {
+            ORE.emitOptimizationRemarkMissedAndAnalysis(
+                DEBUG_TYPE, &I,
+                Twine(Callee->getName()) + " will not be inlined into " +
+                    CS.getCaller()->getName(),
+                Twine("definition of ") + Callee->getName() +
+                    " is not available",
+                /*Verbose=*/true);
             continue;
+          }
 
         CallSites.push_back(std::make_pair(CS, -1));
       }