[PATCH] D56144: [LoopSimplifyCFG] Form LCSSA when a parent loop becomes a sibling

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: uabelho, skatkov, fedor.sergeev, reames.

During the transforms in LoopSimplifyCFG, when we remove a dead exiting edge, the
parent loop may stop being reachable from the child loop, and therefore they become
siblings. If the former child loop had uses of some values from its former parent loop,
now such uses will require LCSSA Phis, even if they were'nt needed before. So we must
form LCSSA for all loops that stopped being ancestors of the current loop in this case.


https://reviews.llvm.org/D56144

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
@@ -3,9 +3,6 @@
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -passes='require<domtree>,loop(simplify-cfg)' -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -loop-simplifycfg -enable-mssa-loop-dependency=true -verify-memoryssa -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
-; XFAIL: *
-; test_01 is currently failing because the loop is not in LCSSA form after the
-; transform.
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 
@@ -56,6 +53,24 @@
 }
 
 define void @test_01() {
+; CHECK-LABEL: @test_01(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+; CHECK:       for.cond.loopexit:
+; CHECK-NEXT:    br label [[FOR_COND]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    [[INC41_LCSSA3:%.*]] = phi i16 [ undef, [[FOR_COND_LOOPEXIT:%.*]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    switch i32 0, label [[FOR_COND_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[FOR_COND_LOOPEXIT]]
+; CHECK-NEXT:    ]
+; CHECK:       for.cond-split:
+; CHECK-NEXT:    [[INC41_LCSSA3_LCSSA:%.*]] = phi i16 [ [[INC41_LCSSA3]], [[FOR_COND]] ]
+; CHECK-NEXT:    br label [[WHILE_COND:%.*]]
+; CHECK:       while.cond:
+; CHECK-NEXT:    [[INC41:%.*]] = phi i16 [ [[INC4:%.*]], [[WHILE_COND]] ], [ [[INC41_LCSSA3_LCSSA]], [[FOR_COND_SPLIT]] ]
+; CHECK-NEXT:    [[INC4]] = add nsw i16 [[INC41]], 1
+; CHECK-NEXT:    br label [[WHILE_COND]]
+;
 entry:
   br label %for.cond
 
Index: lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -378,6 +378,15 @@
           StillReachable->addChildLoop(&L);
         else
           LI.addTopLevelLoop(&L);
+
+        // Some values from loops in [OuterLoop, StillReachable) could be used
+        // in the current loop. Now it is not their child anymore, so such uses
+        // require LCSSA Phis.
+        Loop *FixLCSSALoop = OuterLoop;
+        while (FixLCSSALoop->getParentLoop() != StillReachable)
+          FixLCSSALoop = FixLCSSALoop->getParentLoop();
+        assert(FixLCSSALoop && "Should be a loop!");
+        formLCSSARecursively(*FixLCSSALoop, DT, &LI, &SE);
       }
     }
   }


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