[PATCH] D42179: [NewGVN] Re-evaluate phi of ops after moving an instr to new class

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: dberlin, davide, mcrosier.
Herald added a subscriber: Prazek.

[NewGVN] After moving an instr to a new class, re-evaluate phi of ops.

After moving an instruction to a new class, its leader could have
changed, which means we might be able to simplify phi of ops involving
it as expression.


Repository:
  rL LLVM

https://reviews.llvm.org/D42179

Files:
  lib/Transforms/Scalar/NewGVN.cpp
  test/Transforms/NewGVN/pr35074-phi-of-ops-leader-change-after-moving-I.ll


Index: test/Transforms/NewGVN/pr35074-phi-of-ops-leader-change-after-moving-I.ll
===================================================================
--- /dev/null
+++ test/Transforms/NewGVN/pr35074-phi-of-ops-leader-change-after-moving-I.ll
@@ -0,0 +1,36 @@
+; RUN: opt < %s -newgvn -S | FileCheck %s
+
+; CHECK-LABEL: for.cond:
+; CHECK-NEXT: %phiofops = phi i32 [ 0, %entry ], [ %y.0, %for.inc6 ]
+; CHECK-NEXT: %y.0 = phi i32 [ 1, %entry ], [ %inc7, %for.inc6 ]
+
+; CHECK-LABEL: for.body.lr.ph:
+; CHECK-NEXT: %cmp = icmp ugt i32 %phiofops, %y.0
+
+define void @test(i32 %this) {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc6, %entry
+  %y.0 = phi i32 [ 1, %entry ], [ %inc7, %for.inc6 ]
+  br i1 undef, label %for.inc6, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %for.cond
+  %sub = add nsw i32 %y.0, -1
+  %cmp = icmp ugt i32 %sub, %y.0
+  br i1 %cmp, label %for.end, label %for.body4.1
+
+for.end:                                          ; preds = %for.body4.1, %for.body.lr.ph
+  ret void
+
+for.inc6:                                         ; preds = %for.cond
+  %inc7 = add nuw nsw i32 %y.0, 1
+  br label %for.cond
+
+for.body4.1:                                      ; preds = %for.body.lr.ph
+  %inc.1 = add nuw nsw i32 %y.0, 1
+  tail call void @_blah(i32 %inc.1)
+  br label %for.end
+}
+
+declare void @_blah(i32)
Index: lib/Transforms/Scalar/NewGVN.cpp
===================================================================
--- lib/Transforms/Scalar/NewGVN.cpp
+++ lib/Transforms/Scalar/NewGVN.cpp
@@ -2409,6 +2409,9 @@
       moveValueToNewCongruenceClass(I, E, IClass, EClass);
       markPhiOfOpsChanged(E);
     }
+    // After moving I to the new class, its leader could have changed, which
+    // means that we might be able to simplify phi of ops involving it.
+    markPhiOfOpsChanged(createVariableOrConstant(I));
 
     markUsersTouched(I);
     if (MemoryAccess *MA = getMemoryAccess(I))


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