IR printing improvement for loop passes

Summary:
Loop-pass printing is somewhat deficient since it does not provide the
context around the loop (e.g. preheader). This context information becomes
pretty essential when analyzing transformations that move stuff out of the loop.

Extending printLoop to cover preheader and exit blocks (if any).

Reviewers: sanjoy, silvas, weimingz

Reviewed By: sanjoy

Subscribers: apilipenko, skatkov, llvm-commits

Differential Revision: https://reviews.llvm.org/D40246

llvm-svn: 318878

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index c6019f267a3..9a223df9394 100644
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -732,11 +732,30 @@ PreservedAnalyses LoopPrinterPass::run(Function &F,
 
 void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
   OS << Banner;
+
+  auto *PreHeader = L.getLoopPreheader();
+  if (PreHeader) {
+    OS << "\n; Preheader:";
+    PreHeader->print(OS);
+    OS << "\n; Loop:";
+  }
+
   for (auto *Block : L.blocks())
     if (Block)
       Block->print(OS);
     else
       OS << "Printing <null> block";
+
+  SmallVector<BasicBlock *, 8> ExitBlocks;
+  L.getExitBlocks(ExitBlocks);
+  if (!ExitBlocks.empty()) {
+    OS << "\n; Exit blocks";
+    for (auto *Block : ExitBlocks)
+      if (Block)
+        Block->print(OS);
+      else
+        OS << "Printing <null> block";
+  }
 }
 
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