[CGProfile] Don't emit call graph profile edges with zero weight

[lgrey]

Summary

With D112160 and D112164, on a Chrome Mac build this reduces the total size of CGProfile sections by 78% (around 25% eliminated entirely) and total size of object files by 0.14%.

[Bigcheese]

Looks reasonable. Edges with weight 0 shouldn't matter anyway.

llvm/lib/Transforms/Instrumentation/CGProfile.cpp

 
 static bool runCGProfilePass(
     Module &M, function_ref<BlockFrequencyInfo &(Function &)> GetBFI,
     function_ref<TargetTransformInfo &(Function &)> GetTTI, bool LazyBFI) {
   MapVector<std::pair<Function *, Function *>, uint64_t> Counts;
   InstrProfSymtab Symtab;
   auto UpdateCounts = [&](TargetTransformInfo &TTI, Function *F,
                           Function *CalledF, uint64_t NewCount) {
+    if (NewCount == 0)
+      return;
     if (!CalledF || !TTI.isLoweredToCall(CalledF) ||
         CalledF->hasDLLImportStorageClass())
       return;
     uint64_t &Count = Counts[std::make_pair(F, CalledF)];
     Count = SaturatingAdd(Count, NewCount);
   };
   // Ignore error here.  Indirect calls are ignored if this fails.
   (void)(bool) Symtab.create(M);

llvm/test/Instrumentation/cgprofile.ll

 ; RUN: opt < %s -passes cg-profile -S | FileCheck %s
 ; RUN: opt < %s -cg-profile -S | FileCheck %s
 
 declare void @b()
 
 define void @a() !prof !1 {
   call void @b()
   ret void
 }
 
 @foo = common global i32 ()* null, align 8
 declare i32 @func1()
 declare i32 @func2()
 declare i32 @func3()
 declare i32 @func4()
 declare dllimport i32 @func5()
+declare i32 @func6()
 
 define void @freq(i1 %cond) !prof !1 {
   %tmp = load i32 ()*, i32 ()** @foo, align 8
   call i32 %tmp(), !prof !3
   br i1 %cond, label %A, label %B, !prof !2
 A:
   call void @a();
   ret void
 B:
   call void @b();
   ret void
 }
 
 !1 = !{!"function_entry_count", i64 32}
 !2 = !{!"branch_weights", i32 5, i32 10}
-!3 = !{!"VP", i32 0, i64 1600, i64 7651369219802541373, i64 1030, i64 -4377547752858689819, i64 410, i64 -6929281286627296573, i64 150, i64 -2545542355363006406, i64 10, i64 3667884930908592509, i64 0}
+!3 = !{!"VP", i32 0, i64 1600, i64 7651369219802541373, i64 1030, i64 -4377547752858689819, i64 410, i64 -6929281286627296573, i64 150, i64 -2545542355363006406, i64 10, i64 3667884930908592509, i64 1, i64 15435711456043681792, i64 0}
 
 ; CHECK: !llvm.module.flags = !{![[cgprof:[0-9]+]]}
 ; CHECK: ![[cgprof]] = !{i32 5, !"CG Profile", ![[prof:[0-9]+]]}
 ; CHECK: ![[prof]] = !{![[e0:[0-9]+]], ![[e1:[0-9]+]], ![[e2:[0-9]+]], ![[e3:[0-9]+]], ![[e4:[0-9]+]], ![[e5:[0-9]+]], ![[e6:[0-9]+]]}
 ; CHECK: ![[e0]] = !{void ()* @a, void ()* @b, i64 32}
 ; CHECK: ![[e1]] = !{void (i1)* @freq, i32 ()* @func4, i64 1030}
 ; CHECK: ![[e2]] = !{void (i1)* @freq, i32 ()* @func2, i64 410}
 ; CHECK: ![[e3]] = !{void (i1)* @freq, i32 ()* @func3, i64 150}
 ; CHECK: ![[e4]] = !{void (i1)* @freq, i32 ()* @func1, i64 10}
 ; CHECK: ![[e5]] = !{void (i1)* @freq, void ()* @a, i64 11}
 ; CHECK: ![[e6]] = !{void (i1)* @freq, void ()* @b, i64 21}
-; CHECK-NOT: !{void (i1)* @freq, void ()* @func5, i64 0}
+; CHECK-NOT: !{void (i1)* @freq, void ()* @func5, i64 1}
+; CHECK-NOT: !{void (i1)* @freq, void ()* @func6, i64 0}