[PATCH] D136102: [LoopSimplify] Update loop-metadata ID after loop-simplify splitting out new outer loop

[MengXuan Cai via Phabricator via llvm-commits]

Narutoworld created this revision.
Narutoworld added reviewers: nikic, kazu.
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Narutoworld requested review of this revision.

This patch tries to fix bug-57603 <https://github.com/llvm/llvm-project/issues/57603>.

LoopSimplify creates nested loop to canonicalize those who have more than one latches.
However, the current code forgets to update the loop metadata ID for the newly created loop. 
As a result, more than one loop shares the same loop ID.
This patch aims to resolve this issue.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D136102

Files:
  llvm/lib/Transforms/Utils/LoopSimplify.cpp
  llvm/test/Transforms/LoopSimplify/update_separate_loop_metadata.ll


Index: llvm/test/Transforms/LoopSimplify/update_separate_loop_metadata.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopSimplify/update_separate_loop_metadata.ll
@@ -0,0 +1,47 @@
+; Tests loop-simplify updates the newly created outter loop metadata with
+; a new loop id and keeps other MDNode as before.
+
+; RUN: opt < %s -passes=loop-simplify -S | FileCheck %s
+; CHECK-LABEL: while.body.thread:
+; CHECK: br label %while.cond, !llvm.loop !5
+; CHECK-LABEL: while.body:
+; CHECK: br label %while.cond.outer, !llvm.loop !7
+
+define i16 @foo() {
+entry:
+  br label %while.cond
+
+while.cond:                                       ; preds = %while.body.thread, %while.body, %entry
+  %i.0 = phi i16 [ 0, %entry ], [ %inc4, %while.body.thread ], [ %inc, %while.body ]
+  %j.0 = phi i16 [ 0, %entry ], [ %j.0, %while.body.thread ], [ %spec.select7, %while.body ]
+  %cmp = icmp slt i16 %i.0, 10
+  br i1 %cmp, label %while.body.thread, label %lor.end
+
+while.body.thread:                                ; preds = %while.cond
+  %inc4 = add nsw i16 %i.0, 1
+  br label %while.cond, !llvm.loop !5
+
+lor.end:                                          ; preds = %while.cond
+  %cmp1.not = icmp eq i16 %j.0, 5
+  br i1 %cmp1.not, label %while.end, label %while.body
+
+while.body:                                       ; preds = %lor.end
+  %inc = add nuw nsw i16 %i.0, 1
+  %cmp2 = icmp eq i16 %inc, 12
+  %spec.select7 = select i1 %cmp2, i16 5, i16 %j.0
+  br label %while.cond, !llvm.loop !5
+
+while.end:                                        ; preds = %lor.end
+  ret i16 %i.0
+}
+
+!llvm.module.flags = !{!0, !1, !2, !3}
+!llvm.ident = !{!4}
+
+!0 = !{i32 7, !"Dwarf Version", i32 4}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = !{i32 1, !"wchar_size", i32 1}
+!3 = !{i32 7, !"frame-pointer", i32 2}
+!4 = !{!"clang version 16.0.0.prerel"}
+!5 = distinct !{!5, !6}
+!6 = !{!"llvm.loop.usefulinfo"}                   ; MDString used to represent any metadata
\ No newline at end of file
Index: llvm/lib/Transforms/Utils/LoopSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -333,6 +333,26 @@
   // process of separating the outer one.
   formDedicatedExitBlocks(L, DT, LI, MSSAU, PreserveLCSSA);
 
+  // Create new metadata ID for NewOuter loop
+  // keep other metadata attched before
+  BasicBlock *LatchBlock = NewOuter->getLoopLatch();
+  if (LatchBlock) {
+    unsigned LoopMDKind = LatchBlock->getContext().getMDKindID("llvm.loop");
+    Instruction *TI = LatchBlock->getTerminator();
+    if (TI) {
+      MDNode *LoopMD = TI->getMetadata(LoopMDKind);
+      if (LoopMD) {
+        // Save space for the self-referential LoopID.
+        SmallVector<Metadata *, 4> MDs = {nullptr};
+        for (unsigned i = 1; i < LoopMD->getNumOperands(); ++i)
+          MDs.push_back(LoopMD->getOperand(i));
+        MDNode *NewLoopID = MDNode::getDistinct(LoopMD->getContext(), MDs);
+        NewLoopID->replaceOperandWith(0, NewLoopID);
+        TI->setMetadata(LoopMDKind, NewLoopID);
+      }
+    }
+  }
+
   if (PreserveLCSSA) {
     // Fix LCSSA form for L. Some values, which previously were only used inside
     // L, can now be used in NewOuter loop. We need to insert phi-nodes for them


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