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

[Ruoyu Qiu via llvm-commits]

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

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

Fixes: 148579

>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] 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()) {