[DAGCombiner] Use generalized pattern matcher in foldBoolSelectToLogic

[ChunyuLiao]

support vp.select

TODO: Possibly other functions could be supported, eg: SimplifySelect()

[llvmbot]

@llvm/pr-subscribers-llvm-selectiondag

@llvm/pr-subscribers-backend-risc-v

Author: Liao Chunyu (ChunyuLiao)

Changes

Combine:
RISCVISD::VMAND_VL x, 0/1, y -> 0/x
RISCVISD::VMXOR_VL x, 0/1, y -> x/1

td:
riscv_vmor_vl + riscv_vmand_vl + riscv_vmnot_vl,
better to select
vmorn.mm v0, v8, v0
instead of
vmand.mm v8, v8, v0
vmorn.mm v0, v8, v0

---

Full diff: https://github.com/llvm/llvm-project/pull/79101.diff

3 Files Affected:

• (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+26)
• (modified) llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td (+5)
• (modified) llvm/test/CodeGen/RISCV/rvv/vselect-vp.ll (+20)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 76e8d21b818b259..cd8ced502e8bf3b 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -15621,6 +15621,32 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
     }
     break;
   }
+  case RISCVISD::VMAND_VL: {
+    SDValue N0 = N->getOperand(0);
+    SDValue N1 = N->getOperand(1);
+    if (isNullOrNullSplat(N0))
+      return N0;
+    else if (isNullOrNullSplat(N1))
+      return N1;
+    else if (isOneOrOneSplat(N0))
+      return N1;
+    else if (isOneOrOneSplat(N1))
+      return N0;
+    break;
+  }
+  case RISCVISD::VMOR_VL: {
+    SDValue N0 = N->getOperand(0);
+    SDValue N1 = N->getOperand(1);
+    if (isNullOrNullSplat(N1))
+      return N0;
+    else if (isNullOrNullSplat(N0))
+      return N1;
+    else if (isOneOrOneSplat(N0))
+      return N0;
+    else if (isOneOrOneSplat(N1))
+      return N1;
+    break;
+  }
   case ISD::SRA:
     if (SDValue V = performSRACombine(N, DAG, Subtarget))
       return V;
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td b/llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td
index 6e7be2647e8f838..1f0a7d2e4fd752e 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td
@@ -2736,6 +2736,11 @@ foreach mti = AllMasks in {
                                         VLOpFrag)),
               (!cast<Instruction>("PseudoVMANDN_MM_" # mti.LMul.MX)
                    VR:$rs1, VR:$rs2, GPR:$vl, mti.Log2SEW)>;
+    def : Pat<(mti.Mask (riscv_vmor_vl (riscv_vmand_vl VR:$rs1, VR:$rs2, VLOpFrag),
+                                       (riscv_vmnot_vl VR:$rs2, VLOpFrag),
+                                       VLOpFrag)),
+              (!cast<Instruction>("PseudoVMORN_MM_" # mti.LMul.MX)
+                   VR:$rs1, VR:$rs2, GPR:$vl, mti.Log2SEW)>;
     def : Pat<(mti.Mask (riscv_vmor_vl VR:$rs1,
                                        (riscv_vmnot_vl VR:$rs2, VLOpFrag),
                                        VLOpFrag)),
diff --git a/llvm/test/CodeGen/RISCV/rvv/vselect-vp.ll b/llvm/test/CodeGen/RISCV/rvv/vselect-vp.ll
index 9e7df5eab8dda98..72749368cc07e28 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vselect-vp.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/vselect-vp.ll
@@ -745,3 +745,23 @@ define <vscale x 16 x double> @select_nxv16f64(<vscale x 16 x i1> %a, <vscale x
   %v = call <vscale x 16 x double> @llvm.vp.select.nxv16f64(<vscale x 16 x i1> %a, <vscale x 16 x double> %b, <vscale x 16 x double> %c, i32 %evl)
   ret <vscale x 16 x double> %v
 }
+
+define <vscale x 2 x i1> @select_zero(<vscale x 2 x i1> %x, <vscale x 2 x i1> %y, <vscale x 2 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: select_zero:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e8, mf4, ta, ma
+; CHECK-NEXT:    vmand.mm v0, v8, v0
+; CHECK-NEXT:    ret
+  %a = call <vscale x 2 x i1> @llvm.vp.select.nxv2i1(<vscale x 2 x i1> %x, <vscale x 2 x i1> %y, <vscale x 2 x i1> zeroinitializer, i32 %evl)
+  ret <vscale x 2 x i1> %a
+}
+
+define <vscale x 2 x i1> @select_one(<vscale x 2 x i1> %x, <vscale x 2 x i1> %y, <vscale x 2 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: select_one:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e8, mf4, ta, ma
+; CHECK-NEXT:    vmorn.mm v0, v8, v0
+; CHECK-NEXT:    ret
+  %a = call <vscale x 2 x i1> @llvm.vp.select.nxv2i1(<vscale x 2 x i1> %x, <vscale x 2 x i1> %y, <vscale x 2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer), i32 %evl)
+  ret <vscale x 2 x i1> %a
+}

[topperc]

Isn't this a missed optimization on vp.select? Can we fix it there?

[ChunyuLiao]

number on the left I'm not sure it's generic

1. If it's not a generic case then the example can be removed
2. If it is generic, then it can be optimized again

[lukel97]

Is it possible to make this target agnostic and do this in DAGCombiner.cpp?

[topperc]

I agree that would be better.

[wangpc-pp]

Or in InstCombine? I remember that we have plan to extend InstCombine to handle VP intrinsics: https://llvm.org/docs/Proposals/VectorPredication.html#lift-instsimplify-instcombine-dagcombiner-to-vp

[topperc]

Or in InstCombine? I remember that we have plan to extend InstCombine to handle VP intrinsics: https://llvm.org/docs/Proposals/VectorPredication.html#lift-instsimplify-instcombine-dagcombiner-to-vp

We can't do it in InstCombine. Select blocks poison propagation, but and/or does not.

SelectionDAG is kind of bad about handling poison correctly. It already does this transform for ISD::VSELECT so doing it for VP_SELECT isn't any worse.

[topperc]

Shouldn't this be VPMatchContext?

[topperc]

This doesn't seem to be applying the VL

[topperc]

LGTM

[lukel97]

LGTM