[llvm] Fix clang crash with -print-changed=dot-cfg (PR #148844)

[Ruoyu Qiu via llvm-commits]

https://github.com/cabbaken updated https://github.com/llvm/llvm-project/pull/148844

>From aa2a56a651903a27084f1ba4fe97e7913118caac Mon Sep 17 00:00:00 2001
From: Ruoyu Qiu <qiuruoyu at xiaomi.com>
Date: Tue, 15 Jul 2025 12:49:04 +0000
Subject: [PATCH 1/2] Fix clang crash with -print-changed=dot-cfg

Remove unnecessary comparison of Before and After `DCData`,
which will cause an error when create `DotCfgDiff`.

Signed-off-by: Ruoyu Qiu <cabbaken at outlook.com>
---
 llvm/lib/Passes/StandardInstrumentations.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/llvm/lib/Passes/StandardInstrumentations.cpp b/llvm/lib/Passes/StandardInstrumentations.cpp
index 0623e66772047..bbd8ca430139c 100644
--- a/llvm/lib/Passes/StandardInstrumentations.cpp
+++ b/llvm/lib/Passes/StandardInstrumentations.cpp
@@ -1991,6 +1991,11 @@ DotCfgDiff::DotCfgDiff(StringRef Title, const FuncDataT<DCData> &Before,
       EdgesMap.insert({Key, BeforeColour});
     }
   }
+  if (Before == After) {
+    for (auto &I : Nodes)
+      I.finalize(*this);
+    return;
+  }
 
   // Handle each basic block in the after IR
   for (auto &A : After.getData()) {

>From 88a7e60d0e05dff6678c2f7bb6bff6010e58e629 Mon Sep 17 00:00:00 2001
From: Ruoyu Qiu <cabbaken at outlook.com>
Date: Mon, 21 Jul 2025 05:21:05 +0000
Subject: [PATCH 2/2] Modify testcase and add support numberic label which has
 empty EntryBlockName

Signed-off-by: Ruoyu Qiu <cabbaken at outlook.com>
---
 llvm/lib/Passes/StandardInstrumentations.cpp               | 7 ++++++-
 .../Other/ChangePrinters/DotCfg/print-changed-dot-cfg.ll   | 2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Passes/StandardInstrumentations.cpp b/llvm/lib/Passes/StandardInstrumentations.cpp
index bbd8ca430139c..0abf77b65e5a4 100644
--- a/llvm/lib/Passes/StandardInstrumentations.cpp
+++ b/llvm/lib/Passes/StandardInstrumentations.cpp
@@ -727,8 +727,13 @@ template <typename T>
 template <typename FunctionT>
 bool IRComparer<T>::generateFunctionData(IRDataT<T> &Data, const FunctionT &F) {
   if (shouldGenerateData(F)) {
-    FuncDataT<T> FD(F.front().getName().str());
     int I = 0;
+    std::string FDEntryBlockName = F.front().getName().str();
+    // Basic block with numberic label will be empty here.
+    if (FDEntryBlockName.empty()) {
+      FDEntryBlockName = formatv("{0}", I);
+    }
+    FuncDataT<T> FD(FDEntryBlockName);
     for (const auto &B : F) {
       std::string BBName = B.getName().str();
       if (BBName.empty()) {
diff --git a/llvm/test/Other/ChangePrinters/DotCfg/print-changed-dot-cfg.ll b/llvm/test/Other/ChangePrinters/DotCfg/print-changed-dot-cfg.ll
index a3d5c60fe932d..535d8aee497a3 100644
--- a/llvm/test/Other/ChangePrinters/DotCfg/print-changed-dot-cfg.ll
+++ b/llvm/test/Other/ChangePrinters/DotCfg/print-changed-dot-cfg.ll
@@ -110,7 +110,7 @@
 ; RUN: FileCheck %s -input-file=%t/passes.html --check-prefix=CHECK-DOT-CFG-QUIET-MULT-PASSES-FILTER-FUNC
 
 define i32 @g() {
-entry:
+1:
   %a = add i32 2, 3
   ret i32 %a
 }