[PATCH] D54841: [LoopSimplifyCFG] Don't delete LCSSA Phis

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev updated this revision to Diff 175084.

https://reviews.llvm.org/D54841

Files:
  lib/Transforms/Scalar/LoopSimplifyCFG.cpp
  test/Transforms/LoopSimplifyCFG/lcssa.ll


Index: test/Transforms/LoopSimplifyCFG/lcssa.ll
===================================================================
--- test/Transforms/LoopSimplifyCFG/lcssa.ll
+++ test/Transforms/LoopSimplifyCFG/lcssa.ll
@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
+; RUN: opt -S -passes='require<domtree>,loop(simplify-cfg)' -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
+; RUN: opt -S -loop-simplifycfg -enable-mssa-loop-dependency=true -verify-memoryssa -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+define void @c() {
+; CHECK-LABEL: @c(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[D:%.*]]
+; CHECK:       d.loopexit:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i32 [ [[TMP1:%.*]], [[FOR_COND:%.*]] ]
+; CHECK-NEXT:    br label [[D]]
+; CHECK:       d:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi i32 [ undef, [[ENTRY:%.*]] ], [ [[DOTLCSSA]], [[D_LOOPEXIT:%.*]] ]
+; CHECK-NEXT:    br label [[FOR_COND]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    [[TMP1]] = phi i32 [ [[TMP0]], [[D]] ], [ 0, [[IF_END:%.*]] ]
+; CHECK-NEXT:    [[TOBOOL2:%.*]] = icmp eq i32 [[TMP1]], 0
+; CHECK-NEXT:    br i1 [[TOBOOL2]], label [[IF_END]], label [[D_LOOPEXIT]]
+; CHECK:       if.end:
+; CHECK-NEXT:    br label [[FOR_COND]]
+;
+entry:
+  br label %d
+
+d.loopexit:                                       ; preds = %if.end.7, %for.body
+  %.lcssa = phi i32 [ %1, %for.body ], [ 0, %if.end.7 ]
+  br label %d
+
+d:                                                ; preds = %d.loopexit, %entry
+  %0 = phi i32 [ undef, %entry ], [ %.lcssa, %d.loopexit ]
+  br label %for.cond
+
+for.cond:                                         ; preds = %if.end.8, %d
+  %1 = phi i32 [ %0, %d ], [ 0, %if.end.8 ]
+  br label %for.body
+
+for.body:                                         ; preds = %for.cond
+  %tobool2 = icmp eq i32 %1, 0
+  br i1 %tobool2, label %if.end, label %d.loopexit
+
+if.end:                                           ; preds = %for.body
+  br label %if.end.7
+
+if.end.7:                                         ; preds = %if.end
+  br i1 true, label %if.end.8, label %d.loopexit
+
+if.end.8:                                         ; preds = %if.end.7
+  br label %for.cond
+}
Index: lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -249,7 +249,10 @@
       for (auto *Succ : successors(BB))
         if (Succ != TheOnlySucc) {
           DeadSuccessors.insert(Succ);
-          Succ->removePredecessor(BB);
+          // If our successor lies in a different loop, we don't want to remove
+          // the one-input Phi because it is a LCSSA Phi.
+          bool PreserveLCSSAPhi = !L.contains(Succ);
+          Succ->removePredecessor(BB, PreserveLCSSAPhi);
         }
 
       IRBuilder<> Builder(BB->getContext());


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