[llvm] [GlobalISel] Prefix MatchTable Lines with their Index (PR #125845)

[Pierre van Houtryve via llvm-commits]

https://github.com/Pierre-vh created https://github.com/llvm/llvm-project/pull/125845

I tried to keep it readable by making the width of the column with the index always enough to contain the largest number.
That way things don't shift to the right every time a new digit appears, it remains consistent.

Tests don't break because this only affects the beginning of the line and FileCheck doesn't care about what comes before for the most part.

Example of the new output:
```
     /* 758359 */   // Label 9988: @758359
     /* 758359 */   GIM_Try, /*On fail goto*//*Label 9989*/ GIMT_Encode4(758435), // Rule ID 6715 //
     /* 758364 */     GIM_CheckConstantInt8, /*MI*/0, /*Op*/2, 0,
     /* 758368 */     // MIs[0] offset
```

Fixes #119177

>From 835576db2f011eaa5b09271852729f46d2c9617d Mon Sep 17 00:00:00 2001
From: pvanhout <pierre.vanhoutryve at amd.com>
Date: Wed, 5 Feb 2025 13:07:21 +0100
Subject: [PATCH] [GlobalISel] Prefix MatchTable Lines with their Index

Fixes #119177
---
 .../GlobalISel/GlobalISelMatchTable.cpp       | 23 ++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/llvm/utils/TableGen/Common/GlobalISel/GlobalISelMatchTable.cpp b/llvm/utils/TableGen/Common/GlobalISel/GlobalISelMatchTable.cpp
index 8564bf8d2d91ba5..9083ce7c86a4723 100644
--- a/llvm/utils/TableGen/Common/GlobalISel/GlobalISelMatchTable.cpp
+++ b/llvm/utils/TableGen/Common/GlobalISel/GlobalISelMatchTable.cpp
@@ -286,11 +286,25 @@ MatchTableRecord MatchTable::JumpTarget(unsigned LabelID) {
 void MatchTable::emitUse(raw_ostream &OS) const { OS << "MatchTable" << ID; }
 
 void MatchTable::emitDeclaration(raw_ostream &OS) const {
-  unsigned Indentation = 4;
+  static constexpr unsigned BaseIndent = 4;
+  unsigned Indentation = 0;
   OS << "  constexpr static uint8_t MatchTable" << ID << "[] = {";
   LineBreak.emit(OS, true, *this);
-  OS << std::string(Indentation, ' ');
 
+  const unsigned NumColsForIdx = llvm::to_string(CurrentSize).size();
+
+  unsigned CurIndex = 0;
+  const auto BeginLine = [&](){
+    OS << std::string(BaseIndent, ' ');
+    // To keep the /* index */ column consistent, pad
+    // the string at the start so we can always fit the
+    // exact number of characters to print the largest possible index.
+    std::string IdxStr = llvm::to_string(CurIndex);
+    OS << " /* " << std::string(NumColsForIdx - IdxStr.size(), ' ') << IdxStr << " */ ";
+    OS << std::string(Indentation, ' ');
+  };
+
+  BeginLine();
   for (auto I = Contents.begin(), E = Contents.end(); I != E; ++I) {
     bool LineBreakIsNext = false;
     const auto &NextI = std::next(I);
@@ -306,11 +320,14 @@ void MatchTable::emitDeclaration(raw_ostream &OS) const {
 
     I->emit(OS, LineBreakIsNext, *this);
     if (I->Flags & MatchTableRecord::MTRF_LineBreakFollows)
-      OS << std::string(Indentation, ' ');
+      BeginLine();
 
     if (I->Flags & MatchTableRecord::MTRF_Outdent)
       Indentation -= 2;
+
+    CurIndex += I->size();
   }
+  assert(CurIndex == CurrentSize);
   OS << "}; // Size: " << CurrentSize << " bytes\n";
 }