[llvm] cea0599 - [LangRef] Adds llvm.loop.mustprogress loop metadata

[Atmn Patel via llvm-commits]

Author: Atmn Patel
Date: 2020-11-04T22:32:50-05:00
New Revision: cea0599aa75ba528d077453602945e6d0440f8c3

URL: https://github.com/llvm/llvm-project/commit/cea0599aa75ba528d077453602945e6d0440f8c3
DIFF: https://github.com/llvm/llvm-project/commit/cea0599aa75ba528d077453602945e6d0440f8c3.diff

LOG: [LangRef] Adds llvm.loop.mustprogress loop metadata

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.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D88464

Added: 
    

Modified: 
    llvm/docs/LangRef.rst
    llvm/include/llvm/Analysis/LoopInfo.h
    llvm/lib/Analysis/LoopInfo.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index ff89e0d77448..c9248b49114b 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -6326,6 +6326,15 @@ It is also possible to have nested parallel loops:
    !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
 ^^^^^^^^^^^^^^^^^^^^^^^
 

diff  --git a/llvm/include/llvm/Analysis/LoopInfo.h b/llvm/include/llvm/Analysis/LoopInfo.h
index 8d6a405e0a6d..cf59e4189489 100644
--- a/llvm/include/llvm/Analysis/LoopInfo.h
+++ b/llvm/include/llvm/Analysis/LoopInfo.h
@@ -840,6 +840,9 @@ class Loop : public LoopBase<BasicBlock, Loop> {
   /// 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;
 

diff  --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index 5f741dc595ca..1a6cb50e1e5d 100644
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -539,6 +539,22 @@ void Loop::setLoopAlreadyUnrolled() {
   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();