[PATCH] D88464: [LangRef] Adds llvm.loop.mustprogress loop metadata

[Atmn Patel via Phabricator via llvm-commits]

atmnpatel created this revision.
atmnpatel added reviewers: jdoerfert, nikic, efriedma.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
atmnpatel requested review of this revision.

This patch adds the llvm.loop.mustprogress loop metadata. This is to be
added to loops where the frontend language requires that the loop makes
observable interactions with the environment. This is the loop-level
equivalent to the function attribute `mustprogress` defined in D86233 <https://reviews.llvm.org/D86233>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D88464

Files:
  llvm/docs/LangRef.rst
  llvm/include/llvm/Analysis/LoopInfo.h
  llvm/include/llvm/Transforms/Utils/Cloning.h
  llvm/lib/Analysis/LoopInfo.cpp


Index: llvm/lib/Analysis/LoopInfo.cpp
===================================================================
--- llvm/lib/Analysis/LoopInfo.cpp
+++ llvm/lib/Analysis/LoopInfo.cpp
@@ -535,6 +535,22 @@
   setLoopID(NewLoopID);
 }
 
+void Loop::setLoopMustProgress() {
+  LLVMContext &Context = getHeader()->getContext();
+
+  MDNode *MustProgress = findOptionMDForLoop(this, "llvm.loop.mustprogress");
+
+  if (MustProgress)
+    return;
+
+  MDNode *MustProgressMD =
+      MDNode::get(Context, MDString::get(Context, "llvm.loop.mustprogress"));
+  MDNode *LoopID = getLoopID();
+  MDNode *NewLoopID =
+      makePostTransformationMetadata(Context, LoopID, {}, {MustProgressMD});
+  setLoopID(NewLoopID);
+}
+
 bool Loop::isAnnotatedParallel() const {
   MDNode *DesiredLoopIdMetadata = getLoopID();
 
Index: llvm/include/llvm/Transforms/Utils/Cloning.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/Cloning.h
+++ llvm/include/llvm/Transforms/Utils/Cloning.h
@@ -176,9 +176,9 @@
       function_ref<AssumptionCache &(Function &)> GetAssumptionCache = nullptr,
       ProfileSummaryInfo *PSI = nullptr,
       BlockFrequencyInfo *CallerBFI = nullptr,
-      BlockFrequencyInfo *CalleeBFI = nullptr)
+      BlockFrequencyInfo *CalleeBFI = nullptr, LoopInfo *CalleeLI = nullptr)
       : CG(cg), GetAssumptionCache(GetAssumptionCache), PSI(PSI),
-        CallerBFI(CallerBFI), CalleeBFI(CalleeBFI) {}
+        CallerBFI(CallerBFI), CalleeBFI(CalleeBFI), CalleeLI(CalleeLI) {}
 
   /// If non-null, InlineFunction will update the callgraph to reflect the
   /// changes it makes.
@@ -186,6 +186,7 @@
   function_ref<AssumptionCache &(Function &)> GetAssumptionCache;
   ProfileSummaryInfo *PSI;
   BlockFrequencyInfo *CallerBFI, *CalleeBFI;
+  LoopInfo *CalleeLI;
 
   /// InlineFunction fills this in with all static allocas that get copied into
   /// the caller.
Index: llvm/include/llvm/Analysis/LoopInfo.h
===================================================================
--- llvm/include/llvm/Analysis/LoopInfo.h
+++ llvm/include/llvm/Analysis/LoopInfo.h
@@ -840,6 +840,9 @@
   /// unrolling pass is run more than once (which it generally is).
   void setLoopAlreadyUnrolled();
 
+  /// Add llvm.loop.mustprogress to this loop's loop id metadata.
+  void setLoopMustProgress();
+
   void dump() const;
   void dumpVerbose() const;
 
Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -6257,6 +6257,15 @@
    !3 = distinct !{} ; access group for instructions in the inner loop (which are implicitly contained in outer loop as well)
    !4 = distinct !{} ; access group for instructions in the outer, but not the inner loop
 
+'``llvm.loop.mustprogress``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``llvm.loop.mustprogress`` metadata indicates that this loop is required to
+terminate, unwind, or interact with the environment in an observable way e.g.
+via a volatile memory access, I/O, or other synchronization. If such a loop is
+not found to interact with the environment in an observable way, the loop may
+be removed. This corresponds to the ``mustprogress`` function attribute.
+
 '``irr_loop``' Metadata
 ^^^^^^^^^^^^^^^^^^^^^^^
 


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