[PATCH] D21112: [LoopSimplify] Preserve LCSSA when merging exit blocks.

[Michael Zolotukhin via llvm-commits]

mzolotukhin created this revision.
mzolotukhin added reviewers: chandlerc, sanjoy, bogner.
mzolotukhin added a subscriber: llvm-commits.

This fixes PR26682. Also add LCSSA as a preserved pass to LoopSimplify,
that looks correct to me and allows to write a test for the issue.

http://reviews.llvm.org/D21112

Files:
  lib/Transforms/Utils/LoopSimplify.cpp
  test/Transforms/LoopSimplify/pr26682.ll

Index: test/Transforms/LoopSimplify/pr26682.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopSimplify/pr26682.ll
@@ -0,0 +1,32 @@
+; RUN: opt < %s -lcssa -loop-simplify -indvars -S | FileCheck %s
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-unknown"
+
+ at a = external global i32, align 4
+
+; Check that loop-simplify merges two loop exits, but preserves LCSSA form.
+; CHECK-LABEL: @foo
+; CHECK: for:
+; CHECK: %or.cond = and i1 %cmp1, %cmp2
+; CHECK-NOT: for.cond:
+; CHECK: for.end:
+; CHECK: %a.lcssa = phi i32 [ %a, %for ]
+define i32 @foo(i32 %x) {
+entry:
+  br label %for
+
+for:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %for.cond ]
+  %cmp1 = icmp eq i32 %x, 0
+  %iv.next = add nuw nsw i32 %iv, 1
+  %a = load i32, i32* @a
+  br i1 %cmp1, label %for.cond, label %for.end
+
+for.cond:
+  %cmp2 = icmp slt i32 %iv.next, 4
+  br i1 %cmp2, label %for, label %for.end
+
+for.end:
+  %a.lcssa = phi i32 [ %a, %for ], [ %a, %for.cond ]
+  ret i32 %a.lcssa
+}
Index: lib/Transforms/Utils/LoopSimplify.cpp
===================================================================
--- lib/Transforms/Utils/LoopSimplify.cpp
+++ lib/Transforms/Utils/LoopSimplify.cpp
@@ -686,8 +686,10 @@
       }
       DT->eraseNode(ExitingBlock);
 
-      BI->getSuccessor(0)->removePredecessor(ExitingBlock);
-      BI->getSuccessor(1)->removePredecessor(ExitingBlock);
+      BI->getSuccessor(0)->removePredecessor(
+          ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
+      BI->getSuccessor(1)->removePredecessor(
+          ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
       ExitingBlock->eraseFromParent();
     }
   }
@@ -748,6 +750,7 @@
       AU.addPreserved<GlobalsAAWrapperPass>();
       AU.addPreserved<ScalarEvolutionWrapperPass>();
       AU.addPreserved<SCEVAAWrapperPass>();
+      AU.addPreservedID(LCSSAID);
       AU.addPreserved<DependenceAnalysisWrapperPass>();
       AU.addPreservedID(BreakCriticalEdgesID);  // No critical edges added.
     }


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