[X86] Post process the DAG after isel to remove vector moves that were added to zero...

We previously avoided inserting these moves during isel in a few cases which is implemented using a whitelist of opcodes. But it's too difficult to generate a perfect list of opcodes to whitelist. Especially with AVX512F without AVX512VL using 512 bit vectors to implement some 128/256 bit operations. Since isel is done bottoms up, we'd have to check the VT and opcode and subtarget in order to determine whether an EXTRACT_SUBREG would be generated for some operations.

So instead of doing that, this patch adds a post processing step that detects when the moves are unnecesssary after isel. At that point any EXTRACT_SUBREGs would have already been created and appear in the DAG. So then we just need to ensure the input to the move isn't one.

Differential Revision: https://reviews.llvm.org/D44289

llvm-svn: 327724

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index bcac241..27a1adb 100644 (file)
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -181,6 +181,7 @@ namespace {
     bool IsProfitableToFold(SDValue N, SDNode *U, SDNode *Root) const override;
 
     void PreprocessISelDAG() override;
+    void PostprocessISelDAG() override;
 
 // Include the pieces autogenerated from the target description.
 #include "X86GenDAGISel.inc"
@@ -752,6 +753,70 @@ void X86DAGToDAGISel::PreprocessISelDAG() {
 }
 
 
+void X86DAGToDAGISel::PostprocessISelDAG() {
+  // Skip peepholes at -O0.
+  if (TM.getOptLevel() == CodeGenOpt::None)
+    return;
+
+  // Attempt to remove vectors moves that were inserted to zero upper bits.
+
+  SelectionDAG::allnodes_iterator Position(CurDAG->getRoot().getNode());
+  ++Position;
+
+  while (Position != CurDAG->allnodes_begin()) {
+    SDNode *N = &*--Position;
+    // Skip dead nodes and any non-machine opcodes.
+    if (N->use_empty() || !N->isMachineOpcode())
+      continue;
+
+    if (N->getMachineOpcode() != TargetOpcode::SUBREG_TO_REG)
+      continue;
+
+    unsigned SubRegIdx = N->getConstantOperandVal(2);
+    if (SubRegIdx != X86::sub_xmm && SubRegIdx != X86::sub_ymm)
+      continue;
+
+    SDValue Move = N->getOperand(1);
+    if (!Move.isMachineOpcode())
+      continue;
+
+    // Make sure its one of the move opcodes we recognize.
+    switch (Move.getMachineOpcode()) {
+    default:
+      continue;
+    case X86::VMOVAPDrr:       case X86::VMOVUPDrr:
+    case X86::VMOVAPSrr:       case X86::VMOVUPSrr:
+    case X86::VMOVDQArr:       case X86::VMOVDQUrr:
+    case X86::VMOVAPDYrr:      case X86::VMOVUPDYrr:
+    case X86::VMOVAPSYrr:      case X86::VMOVUPSYrr:
+    case X86::VMOVDQAYrr:      case X86::VMOVDQUYrr:
+    case X86::VMOVAPDZ128rr:   case X86::VMOVUPDZ128rr:
+    case X86::VMOVAPSZ128rr:   case X86::VMOVUPSZ128rr:
+    case X86::VMOVDQA32Z128rr: case X86::VMOVDQU32Z128rr:
+    case X86::VMOVDQA64Z128rr: case X86::VMOVDQU64Z128rr:
+    case X86::VMOVAPDZ256rr:   case X86::VMOVUPDZ256rr:
+    case X86::VMOVAPSZ256rr:   case X86::VMOVUPSZ256rr:
+    case X86::VMOVDQA32Z256rr: case X86::VMOVDQU32Z256rr:
+    case X86::VMOVDQA64Z256rr: case X86::VMOVDQU64Z256rr:
+      break;
+    }
+
+    SDValue In = Move.getOperand(0);
+    if (!In.isMachineOpcode() ||
+        In.getMachineOpcode() <= TargetOpcode::GENERIC_OP_END)
+      continue;
+
+    // Producing instruction is another vector instruction. We can drop the
+    // move.
+    CurDAG->UpdateNodeOperands(N, N->getOperand(0), In, N->getOperand(2));
+
+    // If the move is now dead, delete it.
+    if (Move.getNode()->use_empty())
+      CurDAG->RemoveDeadNode(Move.getNode());
+  }
+}
+
+
 /// Emit any code that needs to be executed only in the main function.
 void X86DAGToDAGISel::emitSpecialCodeForMain() {
   if (Subtarget->isTargetCygMing()) {

diff --git a/llvm/lib/Target/X86/X86InstrVecCompiler.td b/llvm/lib/Target/X86/X86InstrVecCompiler.td
index 9c3f005..6f0bf4b 100644 (file)
--- a/llvm/lib/Target/X86/X86InstrVecCompiler.td
+++ b/llvm/lib/Target/X86/X86InstrVecCompiler.td
@@ -360,67 +360,6 @@ let Predicates = [HasAVX512, NoVLX] in {
                                  v16i32, loadv4i64, sub_ymm>;
 }
 
-// List of opcodes that guaranteed to zero the upper elements of vector regs.
-// TODO: Ideally this would be a blacklist instead of a whitelist. But SHA
-// intrinsics and some MMX->XMM move instructions that aren't VEX encoded make
-// this difficult. So starting with a couple opcodes used by reduction loops
-// where we explicitly insert zeros.
-class veczeroupper<ValueType vt, RegisterClass RC> :
-  PatLeaf<(vt RC:$src), [{
-    return N->getOpcode() == X86ISD::VPMADDWD ||
-           N->getOpcode() == X86ISD::PSADBW;
-  }]>;
-
-def zeroupperv2f64 : veczeroupper<v2f64, VR128>;
-def zeroupperv4f32 : veczeroupper<v4f32, VR128>;
-def zeroupperv2i64 : veczeroupper<v2i64, VR128>;
-def zeroupperv4i32 : veczeroupper<v4i32, VR128>;
-def zeroupperv8i16 : veczeroupper<v8i16, VR128>;
-def zeroupperv16i8 : veczeroupper<v16i8, VR128>;
-
-def zeroupperv4f64  : veczeroupper<v4f64, VR256>;
-def zeroupperv8f32  : veczeroupper<v8f32, VR256>;
-def zeroupperv4i64  : veczeroupper<v4i64, VR256>;
-def zeroupperv8i32  : veczeroupper<v8i32, VR256>;
-def zeroupperv16i16 : veczeroupper<v16i16, VR256>;
-def zeroupperv32i8  : veczeroupper<v32i8, VR256>;
-
-
-// If we can guarantee the upper elements have already been zeroed we can elide
-// an explicit zeroing.
-multiclass subvector_zero_ellision<RegisterClass RC, ValueType DstTy,
-                                   ValueType SrcTy, ValueType ZeroTy,
-                                   SubRegIndex SubIdx, PatLeaf Zeroupper> {
-  def : Pat<(DstTy (insert_subvector (bitconvert (ZeroTy immAllZerosV)),
-                                     Zeroupper:$src, (iPTR 0))),
-            (SUBREG_TO_REG (i64 0), RC:$src, SubIdx)>;
-}
-
-// 128->256
-defm: subvector_zero_ellision<VR128, v4f64,  v2f64, v8i32, sub_xmm, zeroupperv2f64>;
-defm: subvector_zero_ellision<VR128, v8f32,  v4f32, v8i32, sub_xmm, zeroupperv4f32>;
-defm: subvector_zero_ellision<VR128, v4i64,  v2i64, v8i32, sub_xmm, zeroupperv2i64>;
-defm: subvector_zero_ellision<VR128, v8i32,  v4i32, v8i32, sub_xmm, zeroupperv4i32>;
-defm: subvector_zero_ellision<VR128, v16i16, v8i16, v8i32, sub_xmm, zeroupperv8i16>;
-defm: subvector_zero_ellision<VR128, v32i8,  v16i8, v8i32, sub_xmm, zeroupperv16i8>;
-
-// 128->512
-defm: subvector_zero_ellision<VR128, v8f64,  v2f64, v16i32, sub_xmm, zeroupperv2f64>;
-defm: subvector_zero_ellision<VR128, v16f32, v4f32, v16i32, sub_xmm, zeroupperv4f32>;
-defm: subvector_zero_ellision<VR128, v8i64,  v2i64, v16i32, sub_xmm, zeroupperv2i64>;
-defm: subvector_zero_ellision<VR128, v16i32, v4i32, v16i32, sub_xmm, zeroupperv4i32>;
-defm: subvector_zero_ellision<VR128, v32i16, v8i16, v16i32, sub_xmm, zeroupperv8i16>;
-defm: subvector_zero_ellision<VR128, v64i8,  v16i8, v16i32, sub_xmm, zeroupperv16i8>;
-
-// 256->512
-defm: subvector_zero_ellision<VR256, v8f64,  v4f64,  v16i32, sub_ymm, zeroupperv4f64>;
-defm: subvector_zero_ellision<VR256, v16f32, v8f32,  v16i32, sub_ymm, zeroupperv8f32>;
-defm: subvector_zero_ellision<VR256, v8i64,  v4i64,  v16i32, sub_ymm, zeroupperv4i64>;
-defm: subvector_zero_ellision<VR256, v16i32, v8i32,  v16i32, sub_ymm, zeroupperv8i32>;
-defm: subvector_zero_ellision<VR256, v32i16, v16i16, v16i32, sub_ymm, zeroupperv16i16>;
-defm: subvector_zero_ellision<VR256, v64i8,  v32i8,  v16i32, sub_ymm, zeroupperv32i8>;
-
-
 class maskzeroupper<ValueType vt, RegisterClass RC> :
   PatLeaf<(vt RC:$src), [{
     return isMaskZeroExtended(N);

diff --git a/llvm/test/CodeGen/X86/avg.ll b/llvm/test/CodeGen/X86/avg.ll
index 3f96f72..0439c87 100644 (file)
--- a/llvm/test/CodeGen/X86/avg.ll
+++ b/llvm/test/CodeGen/X86/avg.ll
@@ -507,7 +507,6 @@ define void @avg_v48i8(<48 x i8>* %a, <48 x i8>* %b) nounwind {
 ; AVX512BW-NEXT:    vinserti64x4 $1, %ymm1, %zmm2, %zmm1
 ; AVX512BW-NEXT:    vpmovwb %zmm1, %ymm1
 ; AVX512BW-NEXT:    vpmovdw %zmm0, %ymm0
-; AVX512BW-NEXT:    vmovdqa %ymm0, %ymm0
 ; AVX512BW-NEXT:    vpmovwb %zmm0, %ymm0
 ; AVX512BW-NEXT:    vinserti64x4 $1, %ymm0, %zmm1, %zmm0
 ; AVX512BW-NEXT:    vmovdqu %ymm1, (%rax)

diff --git a/llvm/test/CodeGen/X86/bitcast-setcc-128.ll b/llvm/test/CodeGen/X86/bitcast-setcc-128.ll
index 5164d4f..599e907 100644 (file)
--- a/llvm/test/CodeGen/X86/bitcast-setcc-128.ll
+++ b/llvm/test/CodeGen/X86/bitcast-setcc-128.ll
@@ -658,7 +658,6 @@ define i64 @v16i8_widened_with_zeroes(<16 x i8> %a, <16 x i8> %b) {
 ; AVX2-LABEL: v16i8_widened_with_zeroes:
 ; AVX2:       # %bb.0: # %entry
 ; AVX2-NEXT:    vpcmpeqb %xmm1, %xmm0, %xmm0
-; AVX2-NEXT:    vmovdqa %xmm0, %xmm0
 ; AVX2-NEXT:    vpmovmskb %ymm0, %eax
 ; AVX2-NEXT:    vzeroupper
 ; AVX2-NEXT:    retq

diff --git a/llvm/test/CodeGen/X86/merge-consecutive-loads-256.ll b/llvm/test/CodeGen/X86/merge-consecutive-loads-256.ll
index 0f2cf59..73abda4 100644 (file)
--- a/llvm/test/CodeGen/X86/merge-consecutive-loads-256.ll
+++ b/llvm/test/CodeGen/X86/merge-consecutive-loads-256.ll
@@ -597,7 +597,6 @@ define <4 x double> @merge_4f64_f64_34uz_volatile(double* %ptr) nounwind uwtable
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; AVX-NEXT:    vmovhpd {{.*#+}} xmm0 = xmm0[0],mem[0]
-; AVX-NEXT:    vmovapd %xmm0, %xmm0
 ; AVX-NEXT:    retq
 ;
 ; X32-AVX-LABEL: merge_4f64_f64_34uz_volatile:
@@ -605,7 +604,6 @@ define <4 x double> @merge_4f64_f64_34uz_volatile(double* %ptr) nounwind uwtable
 ; X32-AVX-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X32-AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; X32-AVX-NEXT:    vmovhpd {{.*#+}} xmm0 = xmm0[0],mem[0]
-; X32-AVX-NEXT:    vmovapd %xmm0, %xmm0
 ; X32-AVX-NEXT:    retl
   %ptr0 = getelementptr inbounds double, double* %ptr, i64 3
   %ptr1 = getelementptr inbounds double, double* %ptr, i64 4

diff --git a/llvm/test/CodeGen/X86/vector-shuffle-variable-256.ll b/llvm/test/CodeGen/X86/vector-shuffle-variable-256.ll
index c726a14..38c4a11 100644 (file)
--- a/llvm/test/CodeGen/X86/vector-shuffle-variable-256.ll
+++ b/llvm/test/CodeGen/X86/vector-shuffle-variable-256.ll
@@ -136,7 +136,6 @@ define <4 x i64> @var_shuffle_v4i64_v4i64_xx00_i64(<4 x i64> %x, i64 %i0, i64 %i
 ; ALL-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; ALL-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
 ; ALL-NEXT:    vmovlhps {{.*#+}} xmm0 = xmm1[0],xmm0[0]
-; ALL-NEXT:    vmovaps %xmm0, %xmm0
 ; ALL-NEXT:    movq %rbp, %rsp
 ; ALL-NEXT:    popq %rbp
 ; ALL-NEXT:    retq