[PATCH] D154598: [CodeGen] Fix incorrectly detected reduction bug in ComplexDeinterleaving pass

[Igor Kirillov via Phabricator via llvm-commits]

igor.kirillov created this revision.
Herald added subscribers: mgabka, hiraditya.
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igor.kirillov requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

The bug was found after landing D153355 <https://reviews.llvm.org/D153355>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D154598

Files:
  llvm/lib/CodeGen/ComplexDeinterleavingPass.cpp
  llvm/test/CodeGen/AArch64/complex-deinterleaving-reductions.ll


Index: llvm/test/CodeGen/AArch64/complex-deinterleaving-reductions.ll
===================================================================
--- llvm/test/CodeGen/AArch64/complex-deinterleaving-reductions.ll
+++ llvm/test/CodeGen/AArch64/complex-deinterleaving-reductions.ll
@@ -236,4 +236,35 @@
   %.fca.0.1.insert = insertvalue %"struct.std::complex" %.fca.0.0.insert, double %18, 0, 1
   ret %"struct.std::complex" %.fca.0.1.insert
 }
+
+; The reduced bug from D153355. Shows that reduction was detected where it did not exist.
+define void @bug(i1 %exitcond.not) #0 {
+; CHECK-LABEL: bug:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:  .LBB3_1: // %for.body
+; CHECK-NEXT:    // =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    tbz w0, #0, .LBB3_1
+; CHECK-NEXT:  // %bb.2: // %for.end.loopexit
+; CHECK-NEXT:    ret
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %vec_r.0190 = phi <4 x float> [ zeroinitializer, %entry ], [ %lane62, %for.body ]
+  %vec_b.0188 = phi <4 x float> [ zeroinitializer, %entry ], [ %lane76, %for.body ]
+  %add.i175 = fadd <4 x float> %vec_b.0188, %vec_r.0190
+  %vmax2.i = tail call <4 x float> @llvm.aarch64.neon.fmax.v4f32(<4 x float> zeroinitializer, <4 x float> %add.i175)
+  %vmin2.i = tail call <4 x float> @llvm.aarch64.neon.fmin.v4f32(<4 x float> zeroinitializer, <4 x float> %add.i175)
+  %lane62 = shufflevector <4 x float> zeroinitializer, <4 x float> zeroinitializer, <4 x i32> zeroinitializer
+  %lane76 = shufflevector <4 x float> zeroinitializer, <4 x float> zeroinitializer, <4 x i32> zeroinitializer
+  br i1 %exitcond.not, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:                                 ; preds = %for.body
+  %mul.i177 = fmul <4 x float> %lane62, zeroinitializer
+  %mul.i179 = fmul <4 x float> %lane76, zeroinitializer
+  ret void
+}
+
 declare double @llvm.vector.reduce.fadd.v2f64(double, <2 x double>)
+declare <4 x float> @llvm.aarch64.neon.fmax.v4f32(<4 x float>, <4 x float>)
+declare <4 x float> @llvm.aarch64.neon.fmin.v4f32(<4 x float>, <4 x float>)
Index: llvm/lib/CodeGen/ComplexDeinterleavingPass.cpp
===================================================================
--- llvm/lib/CodeGen/ComplexDeinterleavingPass.cpp
+++ llvm/lib/CodeGen/ComplexDeinterleavingPass.cpp
@@ -261,6 +261,10 @@
   PHINode *RealPHI = nullptr;
   PHINode *ImagPHI = nullptr;
 
+  /// Set this flag to true if RealPHI and ImagPHI were reached during reduction
+  /// detection.
+  bool PHIsFound = false;
+
   /// OldToNewPHI maps the original real PHINode to a new, double-sized PHINode.
   /// The new PHINode corresponds to a vector of deinterleaved complex numbers.
   /// This mapping is populated during
@@ -1419,7 +1423,8 @@
       FinalReduction = dyn_cast<Instruction>(U);
     }
 
-    if (NumUsers != 2 || !FinalReduction || FinalReduction->getParent() == B)
+    if (NumUsers != 2 || !FinalReduction || FinalReduction->getParent() == B ||
+        isa<PHINode>(FinalReduction))
       continue;
 
     ReductionInfo[ReductionOp] = {&PHI, FinalReduction};
@@ -1460,6 +1465,7 @@
 
       RealPHI = ReductionInfo[Real].first;
       ImagPHI = ReductionInfo[Imag].first;
+      PHIsFound = false;
       auto Node = identifyNode(Real, Imag);
       if (!Node) {
         std::swap(Real, Imag);
@@ -1467,9 +1473,10 @@
         Node = identifyNode(Real, Imag);
       }
 
-      // If a node is identified, mark its operation instructions as used to
-      // prevent re-identification and attach the node to the real part
-      if (Node) {
+      // If a node is identified and reduction PHINode is used in the chain of
+      // operations, mark its operation instructions as used to prevent
+      // re-identification and attach the node to the real part
+      if (Node && PHIsFound) {
         LLVM_DEBUG(dbgs() << "Identified reduction starting from instructions: "
                           << *Real << " / " << *Imag << "\n");
         Processed[i] = true;
@@ -1762,6 +1769,7 @@
   if (Real != RealPHI || Imag != ImagPHI)
     return nullptr;
 
+  PHIsFound = true;
   NodePtr PlaceholderNode = prepareCompositeNode(
       ComplexDeinterleavingOperation::ReductionPHI, Real, Imag);
   return submitCompositeNode(PlaceholderNode);


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