[PATCH] D80271: [PowerPC] Exploit vabsd for some cases on P9

[EsmeYi via Phabricator via llvm-commits]

Esme created this revision.
Esme added reviewers: steven.zhang, jsji, nemanjai, PowerPC.
Herald added subscribers: llvm-commits, shchenz, kbarton, hiraditya.
Herald added a project: LLVM.

Exploit vabsd for some cases on P9 <https://reviews.llvm.org/P9>, for example:

  void foo (char *restrict p, char *restrict q, char *restrict t)
  {
    for (int i = 0; i < 16; i++)
       t[i] = abs (p[i] - q[i]);
  }

this case should be matched to the HW instruction vabsdub.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80271

Files:
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/test/CodeGen/PowerPC/vec_absd.ll


Index: llvm/test/CodeGen/PowerPC/vec_absd.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/vec_absd.ll
+++ llvm/test/CodeGen/PowerPC/vec_absd.ll
@@ -38,3 +38,45 @@
 ; CHECK: vabsduw 2, 2, 3
 ; CHECK: blr
 }
+
+define <16 x i8> @test_vabsdub(<16 x i8> %0, <16 x i8> %1) {
+entry:
+  %2 = zext <16 x i8> %0 to <16 x i32>
+  %3 = zext <16 x i8> %1 to <16 x i32>
+  %4 = sub nsw <16 x i32> %2, %3
+  %5 = icmp slt <16 x i32> %4, zeroinitializer
+  %6 = sub nsw <16 x i32> zeroinitializer, %4
+  %7 = select <16 x i1> %5, <16 x i32> %6, <16 x i32> %4
+  %8 = trunc <16 x i32> %7 to <16 x i8>
+  ret <16 x i8> %8
+; CHECK-LABEL: @test_vabsdub
+; CHECK: vabsdub 2, 2, 3
+; CHECK: blr
+}
+
+define <8 x i16> @test_vabsduh(<8 x i16> %0, <8 x i16> %1) {
+entry:
+  %2 = zext <8 x i16> %0 to <8 x i32>
+  %3 = zext <8 x i16> %1 to <8 x i32>
+  %4 = sub nsw <8 x i32> %2, %3
+  %5 = icmp slt <8 x i32> %4, zeroinitializer
+  %6 = sub nsw <8 x i32> zeroinitializer, %4
+  %7 = select <8 x i1> %5, <8 x i32> %6, <8 x i32> %4
+  %8 = trunc <8 x i32> %7 to <8 x i16>
+  ret <8 x i16> %8
+; CHECK-LABEL: @test_vabsduh
+; CHECK: vabsduh 2, 2, 3
+; CHECK: blr
+}
+
+define <4 x i32> @test_vabsduw(<4 x i32> %0, <4 x i32> %1) {
+entry:
+  %2 = sub nsw <4 x i32> %0, %1
+  %3 = icmp slt <4 x i32> %2, zeroinitializer
+  %4 = sub nsw <4 x i32> zeroinitializer, %2
+  %5 = select <4 x i1> %3, <4 x i32> %4, <4 x i32> %2
+  ret <4 x i32> %5
+; CHECK-LABEL: @test_vabsduw
+; CHECK: vabsduw 2, 2, 3
+; CHECK: blr
+}
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -16031,6 +16031,24 @@
   SDLoc dl(N);
   SDValue Op0 = N->getOperand(0);

+  // fold (truncate (abs (sub (zext a), (zext b)))) -> (vabsd a, b)
+  if (Subtarget.hasP9Altivec() && Op0.getOpcode() == ISD::ABS) {
+    EVT VT = N->getValueType(0);
+    if (VT != MVT::v4i32 && VT != MVT::v8i16 && VT != MVT::v16i8)
+      return SDValue();
+    SDValue Sub = Op0.getOperand(0);
+    if (Sub.getOpcode() == ISD::SUB) {
+      SDValue SubOp0 = Sub.getOperand(0);
+      SDValue SubOp1 = Sub.getOperand(1);
+      if ((SubOp0.getOpcode() == ISD::ZERO_EXTEND) &&
+          (SubOp1.getOpcode() == ISD::ZERO_EXTEND)) {
+        return DCI.DAG.getNode(PPCISD::VABSD, dl, VT, SubOp0.getOperand(0),
+                               SubOp1.getOperand(0),
+                               DCI.DAG.getTargetConstant(0, dl, MVT::i32));
+      }
+    }
+  }
+  
   // Looking for a truncate of i128 to i64.
   if (Op0.getValueType() != MVT::i128 || N->getValueType(0) != MVT::i64)
     return SDValue();


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