[CFGPrinter] Added command line option to change DOT font

[PysKa-Ratzinger]

This patch introduces the ability to change the fontname used in the DOT graphs of the view-cfg and dot-cfg passes.

This was tested by compiling the bitcode for a simple main.cpp with clang++ -O0 -emit-llvm ./main.cpp -c -o main.bc

int main() { return 0; }

And generating 2 CFG graphs, one without the new argument (to make sure the original behavior is maintained), and another with the new argument, which resulted in the following:

# Generated with opt -p dot-cfg ./main.bc
digraph "CFG for 'main' function" {
	label="CFG for 'main' function";

	Node0x557a6e235010 [shape=record,color="#b70d28ff", style=filled, fillcolor="#b70d2870" fontname="Courier",label="{entry:\l|  %retval = alloca i32, align 4\l  store i32 0, ptr %retval, align 4\l  ret i32 0\l}"];
}

# Generated with opt -p dot-cfg ./main.bc -cfg-fontname=Arial
digraph "CFG for 'main' function" {
	label="CFG for 'main' function";

	Node0x55c9e8286010 [shape=record,color="#b70d28ff", style=filled, fillcolor="#b70d2870" fontname="Arial",label="{entry:\l|  %retval = alloca i32, align 4\l  store i32 0, ptr %retval, align 4\l  ret i32 0\l}"];
}

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[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: PysKa Ratzinger (PysKa-Ratzinger)

Changes

This patch introduces the ability to change the fontname used in the DOT graphs of the view-cfg and dot-cfg passes.

This was tested by compiling the bitcode for a simple main.cpp with clang++ -O0 -emit-llvm ./main.cpp -c -o main.bc

int main() { return 0; }

And generating 2 CFG graphs, one without the new argument (to make sure the original behavior is maintained), and another with the new argument, which resulted in the following:

# Generated with opt -p dot-cfg ./main.bc
digraph "CFG for 'main' function" {
	label="CFG for 'main' function";

	Node0x557a6e235010 [shape=record,color="#b70d28ff", style=filled, fillcolor="#b70d2870" fontname="Courier",label="{entry:\l|  %retval = alloca i32, align 4\l  store i32 0, ptr %retval, align 4\l  ret i32 0\l}"];
}

# Generated with opt -p dot-cfg ./main.bc -cfg-fontname=Arial
digraph "CFG for 'main' function" {
	label="CFG for 'main' function";

	Node0x55c9e8286010 [shape=record,color="#b70d28ff", style=filled, fillcolor="#b70d2870" fontname="Arial",label="{entry:\l|  %retval = alloca i32, align 4\l  store i32 0, ptr %retval, align 4\l  ret i32 0\l}"];
}

---

Full diff: https://github.com/llvm/llvm-project/pull/148403.diff

2 Files Affected:

• (modified) llvm/include/llvm/Analysis/CFGPrinter.h (+10-2)
• (modified) llvm/lib/Analysis/CFGPrinter.cpp (+5)

diff --git a/llvm/include/llvm/Analysis/CFGPrinter.h b/llvm/include/llvm/Analysis/CFGPrinter.h
index ec26da87eb916..8955ada815ed0 100644
--- a/llvm/include/llvm/Analysis/CFGPrinter.h
+++ b/llvm/include/llvm/Analysis/CFGPrinter.h
@@ -27,11 +27,14 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/ProfDataUtils.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/DOTGraphTraits.h"
 #include "llvm/Support/FormatVariadic.h"
 
 namespace llvm {
+LLVM_ABI extern cl::opt<std::string> CFGFontName;
+
 class ModuleSlotTracker;
 
 template <class GraphType> struct GraphTraits;
@@ -321,9 +324,14 @@ struct DOTGraphTraits<DOTFuncInfo *> : public DefaultDOTGraphTraits {
                                 ? (getHeatColor(0))
                                 : (getHeatColor(1));
 
+    std::string FontName = "Courier";
+    if (!CFGFontName.empty()) {
+      FontName = CFGFontName;
+    }
+
     std::string Attrs = "color=\"" + EdgeColor + "ff\", style=filled," +
-                        " fillcolor=\"" + Color + "70\"" +
-                        " fontname=\"Courier\"";
+                        " fillcolor=\"" + Color + "70\"" + " fontname=\"" +
+                        FontName + "\"";
     return Attrs;
   }
   LLVM_ABI bool isNodeHidden(const BasicBlock *Node,
diff --git a/llvm/lib/Analysis/CFGPrinter.cpp b/llvm/lib/Analysis/CFGPrinter.cpp
index 38aad849755be..d7f411ddbf9a4 100644
--- a/llvm/lib/Analysis/CFGPrinter.cpp
+++ b/llvm/lib/Analysis/CFGPrinter.cpp
@@ -26,6 +26,11 @@
 
 using namespace llvm;
 
+cl::opt<std::string>
+    llvm::CFGFontName("cfg-fontname", cl::Hidden,
+                      cl::desc("The name of a font to use for the DOT"
+                               " file (defaults to Courier)"));
+
 static cl::opt<std::string>
     CFGFuncName("cfg-func-name", cl::Hidden,
                 cl::desc("The name of a function (or its substring)"

[PysKa-Ratzinger]

As an aside, the motivation for doing this patch is because "opt view-cfg" by default opens KGraphViewer, which is fine, but zooming into the individual blocks, or zooming out, makes the font very ugly. I'm assuming the font is bitmap on my system?

(zoom out)

(zoom in)

I could make a script to run "opt dot-cfg" first, edit the file to use a ttf font, and then open the file again with KGraphViewer, but there is a secondary problem that I'm looking at heavily templated code, which sometimes explodes the names of the functions and prevents me from using the "dot-cfg" pass, since the name of the file would exceed the max filename allowed on Linux.

So I feel like this was really the only good option.

(with patch zoom in)

(with patch zoom out)