[LTO] Make detection of WPD remark enablement more robust

Summary:
Currently only the first function in the module is checked to
see if it has remarks enabled. If that first function is a declaration,
remarks will be incorrectly skipped. Change to look for the first
non-empty function.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D51556

llvm-svn: 342477

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

@@ -1325,15 +1325,14 @@ void DevirtModule::rebuildGlobal(VTableBits &B) {
 
 bool DevirtModule::areRemarksEnabled() {
   const auto &FL = M.getFunctionList();
-  if (FL.empty())
-    return false;
-  const Function &Fn = FL.front();
-
-  const auto &BBL = Fn.getBasicBlockList();
-  if (BBL.empty())
-    return false;
-  auto DI = OptimizationRemark(DEBUG_TYPE, "", DebugLoc(), &BBL.front());
-  return DI.isEnabled();
+  for (const Function &Fn : FL) {
+    const auto &BBL = Fn.getBasicBlockList();
+    if (BBL.empty())
+      continue;
+    auto DI = OptimizationRemark(DEBUG_TYPE, "", DebugLoc(), &BBL.front());
+    return DI.isEnabled();
+  }
+  return false;
 }
 
 void DevirtModule::scanTypeTestUsers(Function *TypeTestFunc,

llvm/test/ThinLTO/X86/cfi-devirt.ll

@@ -11,6 +11,7 @@
 ; RUN:   -r=%t.o,_ZN1A1nEi,p \
 ; RUN:   -r=%t.o,_ZN1B1fEi,p \
 ; RUN:   -r=%t.o,_ZN1C1fEi,p \
+; RUN:   -r=%t.o,empty,p \
 ; RUN:   -r=%t.o,_ZTV1B, \
 ; RUN:   -r=%t.o,_ZTV1C, \
 ; RUN:   -r=%t.o,_ZN1A1nEi, \
@@ -27,6 +28,7 @@
 ; RUN:   -r=%t.o,_ZN1A1nEi,p \
 ; RUN:   -r=%t.o,_ZN1B1fEi,p \
 ; RUN:   -r=%t.o,_ZN1C1fEi,p \
+; RUN:   -r=%t.o,empty,p \
 ; RUN:   -r=%t.o,_ZTV1B, \
 ; RUN:   -r=%t.o,_ZTV1C, \
 ; RUN:   -r=%t.o,_ZN1A1nEi, \
@@ -48,6 +50,10 @@ target triple = "x86_64-grtev4-linux-gnu"
 @_ZTV1B = constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1fEi to i8*), i8* bitcast (i32 (%struct.A*, i32)* @_ZN1A1nEi to i8*)] }, !type !0, !type !1
 @_ZTV1C = constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.C*, i32)* @_ZN1C1fEi to i8*), i8* bitcast (i32 (%struct.A*, i32)* @_ZN1A1nEi to i8*)] }, !type !0, !type !2
 
+; Put declaration first to test handling of remarks when the first
+; function has no basic blocks.
+declare void @empty()
+
 ; CHECK-IR-LABEL: define i32 @test
 define i32 @test(%struct.A* %obj, i32 %a) {
 entry: