[llvm] [BOLT]Report 0 profile quality gaps if no eligible functions (PR #130810)

[via llvm-commits]

https://github.com/ShatianWang created https://github.com/llvm/llvm-project/pull/130810

Fix a format issue in profile quality gaps reporting introduced in [127954](https://github.com/llvm/llvm-project/pull/127954). 
The profile quality gaps are computed on a subset of eligible functions and basic blocks. For instance, if a function contains a single block, then it is not eligible for the CF flow conservation analysis, meaning that the function will not affect the reported CFG flow conservation gap. 

Previously, when the set of functions or basic blocks for a specific profile quality score is empty, then nothing will be printed for this specific score following the "BOLT-INFO: profile quality metrics..." line. For small test binaries, it is often the case that the eligible sets are empty for all three scores. As a result, the next "BOLT-INFO" will not start a new line. This PR fixes the issue by reporting 0 profile quality gap for each quality metric if the corresponding eligible set is empty. 

Added test `bolt/test/X86/profile-quality-reporting-small-binary.s`.

>From 39112aed99fb6342d2e821896fa35485569ab7e2 Mon Sep 17 00:00:00 2001
From: Shatian Wang <shatian at meta.com>
Date: Tue, 11 Mar 2025 09:05:08 -0700
Subject: [PATCH] Report 0.00% profile quality gaps under empty eligible
 functions / blocks

---
 bolt/lib/Passes/ProfileQualityStats.cpp       | 13 +++++--
 .../profile-quality-reporting-small-binary.s  | 35 +++++++++++++++++++
 2 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 bolt/test/X86/profile-quality-reporting-small-binary.s

diff --git a/bolt/lib/Passes/ProfileQualityStats.cpp b/bolt/lib/Passes/ProfileQualityStats.cpp
index 332c78da8a1e3..61d67b4f9068e 100644
--- a/bolt/lib/Passes/ProfileQualityStats.cpp
+++ b/bolt/lib/Passes/ProfileQualityStats.cpp
@@ -157,8 +157,10 @@ void printCFGContinuityStats(raw_ostream &OS,
     FractionECUnreachables.push_back(FractionECUnreachable);
   }
 
-  if (FractionECUnreachables.empty())
+  if (FractionECUnreachables.empty()) {
+    OS << "function CFG discontinuity 0.00%; ";
     return;
+  }
 
   llvm::sort(FractionECUnreachables);
   const int Rank = int(FractionECUnreachables.size() *
@@ -251,8 +253,10 @@ void printCallGraphFlowConservationStats(
     }
   }
 
-  if (CallGraphGaps.empty())
+  if (CallGraphGaps.empty()) {
+    OS << "call graph flow conservation gap 0.00%; ";
     return;
+  }
 
   llvm::sort(CallGraphGaps);
   const int Rank =
@@ -340,8 +344,11 @@ void printCFGFlowConservationStats(raw_ostream &OS,
     }
   }
 
-  if (CFGGapsWeightedAvg.empty())
+  if (CFGGapsWeightedAvg.empty()) {
+    OS << "CFG flow conservation gap 0.00% (weighted) 0.00% (worst)\n";
     return;
+  }
+
   llvm::sort(CFGGapsWeightedAvg);
   const int RankWA = int(CFGGapsWeightedAvg.size() *
                          opts::PercentileForProfileQualityCheck / 100);
diff --git a/bolt/test/X86/profile-quality-reporting-small-binary.s b/bolt/test/X86/profile-quality-reporting-small-binary.s
new file mode 100644
index 0000000000000..603d5c3218bc3
--- /dev/null
+++ b/bolt/test/X86/profile-quality-reporting-small-binary.s
@@ -0,0 +1,35 @@
+## Test that BOLT-INFO is correctly formatted after profile quality reporting for
+## a small binary.
+
+# RUN: llvm-mc --filetype=obj --triple x86_64-unknown-unknown %s -o %t.o
+# RUN: link_fdata %s %t.o %t.fdata
+# RUN: llvm-strip --strip-unneeded %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.bolt --data=%t.fdata \
+# RUN:     2>&1 | FileCheck %s
+
+# CHECK: BOLT-INFO: profile quality metrics for the hottest 2 functions (reporting top 5% values): function CFG discontinuity 0.00%; call graph flow conservation gap 0.00%; CFG flow conservation gap 0.00% (weighted) 0.00% (worst)
+# CHECK-NEXT: BOLT-INFO:
+
+        .text
+        .globl  func
+        .type   func, @function
+func:
+        pushq   %rbp
+        ret
+LLfunc_end:
+        .size   func, LLfunc_end-func
+
+
+        .globl  main
+        .type   main, @function
+main:
+        pushq   %rbp
+        movq    %rsp, %rbp
+LLmain_func:
+        call    func
+# FDATA: 1 main #LLmain_func# 1 func 0 0 500
+        movl    $4, %edi
+        retq
+.Lmain_end:
+        .size   main, .Lmain_end-main