[PATCH] D27830: Preserve loop metadata when folding branches to a common destination

[Michael Kuperstein via Phabricator via llvm-commits]

mkuper created this revision.
mkuper added reviewers: hfinkel, fhahn, danielcdh.
mkuper added a subscriber: llvm-commits.

https://reviews.llvm.org/D27830

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/LoopSimplify/preserve-llvm-loop-metadata.ll


Index: test/Transforms/LoopSimplify/preserve-llvm-loop-metadata.ll
===================================================================
--- test/Transforms/LoopSimplify/preserve-llvm-loop-metadata.ll
+++ test/Transforms/LoopSimplify/preserve-llvm-loop-metadata.ll
@@ -1,5 +1,6 @@
 ; RUN: opt -loop-simplify -S < %s | FileCheck %s
 
+; CHECK-LABEL: @test1
 define void @test1(i32 %n) {
 entry:
   br label %while.cond
@@ -35,6 +36,33 @@
 ; CHECK: if.else
 ; CHECK-NOT: br {{.*}}!llvm.loop{{.*}}
 
+; CHECK-LABEL: @test2
+; CHECK: for.body:
+; CHECK: br i1 %{{.*}}, label %for.body, label %cleanup.loopexit, !llvm.loop !0
+define void @test2(i32 %k)  {
+entry: 
+  %cmp9 = icmp sgt i32 %k, 0
+  br i1 %cmp9, label %for.body.preheader, label %cleanup
+
+for.body.preheader:                               ; preds = %entry
+  br label %for.body
+
+for.cond:                                         ; preds = %for.body
+  %cmp = icmp slt i32 %inc, %k
+  br i1 %cmp, label %for.body, label %cleanup.loopexit, !llvm.loop !0
+
+for.body:                                         ; preds = %for.body.preheader, %for.cond
+  %i.010 = phi i32 [ %inc, %for.cond ], [ 0, %for.body.preheader ]
+  %cmp3 = icmp sgt i32 %i.010, 3
+  %inc = add nsw i32 %i.010, 1
+  br i1 %cmp3, label %cleanup.loopexit, label %for.cond
+
+cleanup.loopexit:                                 ; preds = %for.body, %for.cond
+  br label %cleanup
+
+cleanup:                                          ; preds = %cleanup.loopexit, %entry
+  ret void
+}
 
 !0 = distinct !{!0, !1}
 !1 = !{!"llvm.loop.distribute.enable", i1 true}
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2792,6 +2792,11 @@
       PBI = New_PBI;
     }
 
+    // If BI was a loop latch, PBI is the new latch. If we have
+    // loop metadata, copy it over.
+    if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
+      PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
+
     // TODO: If BB is reachable from all paths through PredBlock, then we
     // could replace PBI's branch probabilities with BI's.
 


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