[PATCH] D134980: [RISCV] Prevent performCombineVMergeAndVOps from creating cycles in the DAG.

[Craig Topper via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG9273f860c089: [RISCV] Prevent performCombineVMergeAndVOps from creating cycles in the DAG. (authored by craig.topper).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D134980/new/

https://reviews.llvm.org/D134980

Files:
  llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
  llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll


Index: llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll
+++ llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll
@@ -843,3 +843,40 @@
   %b = call <vscale x 2 x i32> @llvm.vp.select.nxv2i32(<vscale x 2 x i1> %m, <vscale x 2 x i32> %a, <vscale x 2 x i32> %passthru, i32 %vl)
   ret <vscale x 2 x i32> %b
 }
+
+; Folding this would create a loop in the DAG becuase the chain from the VLE is
+; used by the vssubu.
+define void @test_dag_loop() {
+; CHECK-LABEL: test_dag_loop:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    vsetivli zero, 1, e16, m8, ta, mu
+; CHECK-NEXT:    vle16.v v8, (zero)
+; CHECK-NEXT:    vsetvli a0, zero, e8, m4, ta, mu
+; CHECK-NEXT:    vmclr.m v0
+; CHECK-NEXT:    vmv.v.i v16, 0
+; CHECK-NEXT:    vsetivli zero, 0, e8, m4, tu, mu
+; CHECK-NEXT:    vmv4r.v v20, v16
+; CHECK-NEXT:    vssubu.vx v20, v16, zero, v0.t
+; CHECK-NEXT:    vsetvli zero, zero, e8, m4, ta, mu
+; CHECK-NEXT:    vmseq.vv v0, v20, v16
+; CHECK-NEXT:    vsetvli a0, zero, e16, m8, ta, mu
+; CHECK-NEXT:    vmv.v.i v16, 0
+; CHECK-NEXT:    vsetivli zero, 1, e16, m8, tu, mu
+; CHECK-NEXT:    vmerge.vvm v16, v16, v8, v0
+; CHECK-NEXT:    vsetivli zero, 0, e16, m8, ta, mu
+; CHECK-NEXT:    vse16.v v16, (zero)
+; CHECK-NEXT:    ret
+entry:
+  %0 = call <vscale x 32 x i16> @llvm.riscv.vle.nxv32i16.i64(<vscale x 32 x i16> undef, <vscale x 32 x i16>* null, i64 1)
+  %1 = tail call <vscale x 32 x i8> @llvm.riscv.vssubu.mask.nxv32i8.i8.i64(<vscale x 32 x i8> zeroinitializer, <vscale x 32 x i8> zeroinitializer, i8 0, <vscale x 32 x i1> zeroinitializer, i64 0, i64 0)
+  %2 = tail call <vscale x 32 x i1> @llvm.riscv.vmseq.nxv32i8.nxv32i8.i64(<vscale x 32 x i8> %1, <vscale x 32 x i8> zeroinitializer, i64 0)
+  %3 = tail call <vscale x 32 x i16> @llvm.riscv.vmerge.nxv32i16.nxv32i16.i64(<vscale x 32 x i16> zeroinitializer, <vscale x 32 x i16> zeroinitializer, <vscale x 32 x i16> %0, <vscale x 32 x i1> %2, i64 1)
+  call void @llvm.riscv.vse.nxv32i16.i64(<vscale x 32 x i16> %3, <vscale x 32 x i16>* null, i64 0)
+  ret void
+}
+
+declare <vscale x 32 x i16> @llvm.riscv.vle.nxv32i16.i64(<vscale x 32 x i16>, <vscale x 32 x i16>* nocapture, i64)
+declare <vscale x 32 x i8> @llvm.riscv.vssubu.mask.nxv32i8.i8.i64(<vscale x 32 x i8>, <vscale x 32 x i8>, i8, <vscale x 32 x i1>, i64, i64 immarg)
+declare <vscale x 32 x i1> @llvm.riscv.vmseq.nxv32i8.nxv32i8.i64(<vscale x 32 x i8>, <vscale x 32 x i8>, i64)
+declare <vscale x 32 x i16> @llvm.riscv.vmerge.nxv32i16.nxv32i16.i64(<vscale x 32 x i16>, <vscale x 32 x i16>, <vscale x 32 x i16>, <vscale x 32 x i1>, i64)
+declare void @llvm.riscv.vse.nxv32i16.i64(<vscale x 32 x i16>, <vscale x 32 x i16>* nocapture, i64)
Index: llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -2667,6 +2667,20 @@
   bool HasChainOp =
       True.getOperand(True.getNumOperands() - 1).getValueType() == MVT::Other;
 
+  if (HasChainOp) {
+    // Avoid creating cycles in the DAG. We must ensure that none of the other
+    // operands depend on True through it's Chain.
+    SmallVector<const SDNode *, 4> LoopWorklist;
+    SmallPtrSet<const SDNode *, 16> Visited;
+    LoopWorklist.push_back(False.getNode());
+    LoopWorklist.push_back(Mask.getNode());
+    LoopWorklist.push_back(VL.getNode());
+    if (SDNode *Glued = N->getGluedNode())
+      LoopWorklist.push_back(Glued);
+    if (SDNode::hasPredecessorHelper(True.getNode(), Visited, LoopWorklist))
+      return false;
+  }
+
   // Need True has same VL with N.
   unsigned TrueVLIndex = True.getNumOperands() - HasChainOp - 2;
   SDValue TrueVL = True.getOperand(TrueVLIndex);


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