[PATCH] D139812: [LoopFusion] sink second loop PHIs

[Arthur Eubanks via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG5004320590ae: [LoopFusion] sink second loop PHIs (authored by caojoshua, committed by aeubanks).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D139812/new/

https://reviews.llvm.org/D139812

Files:
  llvm/lib/Transforms/Scalar/LoopFuse.cpp
  llvm/test/Transforms/LoopFusion/lcssa.ll


Index: llvm/test/Transforms/LoopFusion/lcssa.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopFusion/lcssa.ll
@@ -0,0 +1,79 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=loop-fusion < %s 2>&1 | FileCheck %s
+
+; Tests when the second loop preheader has a phi coming from the first loop
+; exit. If the phi is not used in the second loop, the loops can be fused and
+; the phi is sunk to the fused loop exit. If the phi is used in the second loop,
+; the loops cannot be fused.
+
+define void @test1() {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    br label [[MIDDLE_BLOCK:%.*]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    br i1 true, label [[FOR_END41:%.*]], label [[VECTOR_PH]]
+; CHECK:       for.end41:
+; CHECK-NEXT:    [[DOTLCSSA92:%.*]] = phi i16 [ 1, [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %vector.ph
+
+vector.ph:                                        ; preds = %middle.block, %entry
+  br label %middle.block
+
+middle.block:                                     ; preds = %vector.ph
+  br i1 true, label %for.cond17.preheader, label %vector.ph
+
+for.cond17.preheader:                             ; preds = %middle.block
+  %.lcssa92 = phi i16 [ 1, %middle.block ]
+  br label %vector.ph61
+
+vector.ph61:                                      ; preds = %middle.block59, %for.cond17.preheader
+  br i1 true, label %for.end41, label %vector.ph61
+
+for.end41:                                        ; preds = %middle.block59
+  ret void
+}
+
+define void @test2() {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    br label [[MIDDLE_BLOCK:%.*]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    br i1 true, label [[FOR_COND17_PREHEADER:%.*]], label [[VECTOR_PH]]
+; CHECK:       for.cond17.preheader:
+; CHECK-NEXT:    [[DOTLCSSA92:%.*]] = phi i16 [ 1, [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[VECTOR_PH61:%.*]]
+; CHECK:       vector.ph61:
+; CHECK-NEXT:    call void @a(i16 [[DOTLCSSA92]])
+; CHECK-NEXT:    br i1 true, label [[FOR_END41:%.*]], label [[VECTOR_PH61]]
+; CHECK:       for.end41:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %vector.ph
+
+vector.ph:                                        ; preds = %middle.block, %entry
+  br label %middle.block
+
+middle.block:                                     ; preds = %vector.ph
+  br i1 true, label %for.cond17.preheader, label %vector.ph
+
+for.cond17.preheader:                             ; preds = %middle.block
+  %.lcssa92 = phi i16 [ 1, %middle.block ]
+  br label %vector.ph61
+
+vector.ph61:                                      ; preds = %middle.block59, %for.cond17.preheader
+  call void @a(i16 %.lcssa92)
+  br i1 true, label %for.end41, label %vector.ph61
+
+for.end41:                                        ; preds = %middle.block59
+  ret void
+}
+
+declare void @a(i16);
Index: llvm/lib/Transforms/Scalar/LoopFuse.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopFuse.cpp
+++ llvm/lib/Transforms/Scalar/LoopFuse.cpp
@@ -1064,6 +1064,11 @@
       }
     }
 
+    // PHIs in FC1's header only have FC0 blocks as predecessors. PHIs
+    // cannot be hoisted and should be sunk to the exit of the fused loop.
+    if (isa<PHINode>(I))
+      return false;
+
     // If this isn't a memory inst, hoisting is safe
     if (!I.mayReadOrWriteMemory())
       return true;


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