[PATCH] D38895: [X86] Replace custom scalar integer absolute matching with ISD::ABS lowering.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.

X86 has its own copy of integer absolute pattern matching to combine directly to a SUB+CMOV.

This patch replaces the combine with custom lowering to permit more ISD::ABS combines.

Test cases are mostly covered by iabs.ll (https://reviews.llvm.org/rL315706 and https://reviews.llvm.org/rL315711). I can try to add further scalar ISD::ABS combine tests to combine-abs.ll if you think it useful.


Repository:
  rL LLVM

https://reviews.llvm.org/D38895

Files:
  lib/Target/X86/X86ISelLowering.cpp


Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -188,6 +188,14 @@
   setCondCodeAction(ISD::SETUNE, MVT::f64, Expand);
   setCondCodeAction(ISD::SETUNE, MVT::f80, Expand);
 
+  // Integer absolute.
+  if (Subtarget.hasCMov()) {
+    setOperationAction(ISD::ABS            , MVT::i16  , Custom);
+    setOperationAction(ISD::ABS            , MVT::i32  , Custom);
+    if (Subtarget.is64Bit())
+      setOperationAction(ISD::ABS          , MVT::i64  , Custom);
+  }
+
   // Promote all UINT_TO_FP to larger SINT_TO_FP's, as X86 doesn't have this
   // operation.
   setOperationAction(ISD::UINT_TO_FP       , MVT::i1   , Promote);
@@ -21502,6 +21510,19 @@
 }
 
 static SDValue LowerABS(SDValue Op, SelectionDAG &DAG) {
+  MVT VT = Op.getSimpleValueType();
+  if (VT == MVT::i16 || VT == MVT::i32 || VT == MVT::i64) {
+    // Since X86 does not have CMOV for 8-bit integer, we don't convert
+    // 8-bit integer abs to NEG and CMOV.
+    SDLoc DL(Op);
+    SDValue N0 = Op.getOperand(0);
+    SDValue Neg = DAG.getNode(X86ISD::SUB, DL, DAG.getVTList(VT, MVT::i32),
+                              DAG.getConstant(0, DL, VT), N0);
+    SDValue Ops[] = {N0, Neg, DAG.getConstant(X86::COND_GE, DL, MVT::i8),
+                     SDValue(Neg.getNode(), 1)};
+    return DAG.getNode(X86ISD::CMOV, DL, VT, Ops);
+  }
+
   assert(Op.getSimpleValueType().is256BitVector() &&
          Op.getSimpleValueType().isInteger() &&
          "Only handle AVX 256-bit vector integer operation");
@@ -32780,38 +32801,6 @@
   return SDValue();
 }
 
-/// Generate NEG and CMOV for integer abs.
-static SDValue combineIntegerAbs(SDNode *N, SelectionDAG &DAG) {
-  EVT VT = N->getValueType(0);
-
-  // Since X86 does not have CMOV for 8-bit integer, we don't convert
-  // 8-bit integer abs to NEG and CMOV.
-  if (VT.isInteger() && VT.getSizeInBits() == 8)
-    return SDValue();
-
-  SDValue N0 = N->getOperand(0);
-  SDValue N1 = N->getOperand(1);
-  SDLoc DL(N);
-
-  // Check pattern of XOR(ADD(X,Y), Y) where Y is SRA(X, size(X)-1)
-  // and change it to SUB and CMOV.
-  if (VT.isInteger() && N->getOpcode() == ISD::XOR &&
-      N0.getOpcode() == ISD::ADD && N0.getOperand(1) == N1 &&
-      N1.getOpcode() == ISD::SRA && N1.getOperand(0) == N0.getOperand(0)) {
-    auto *Y1C = dyn_cast<ConstantSDNode>(N1.getOperand(1));
-    if (Y1C && Y1C->getAPIntValue() == VT.getSizeInBits() - 1) {
-      // Generate SUB & CMOV.
-      SDValue Neg = DAG.getNode(X86ISD::SUB, DL, DAG.getVTList(VT, MVT::i32),
-                                DAG.getConstant(0, DL, VT), N0.getOperand(0));
-      SDValue Ops[] = {N0.getOperand(0), Neg,
-                       DAG.getConstant(X86::COND_GE, DL, MVT::i8),
-                       SDValue(Neg.getNode(), 1)};
-      return DAG.getNode(X86ISD::CMOV, DL, VT, Ops);
-    }
-  }
-  return SDValue();
-}
-
 /// Try to turn tests against the signbit in the form of:
 ///   XOR(TRUNCATE(SRL(X, size(X)-1)), 1)
 /// into:
@@ -34393,10 +34382,6 @@
   if (SDValue RV = foldXorTruncShiftIntoCmp(N, DAG))
     return RV;
 
-  if (Subtarget.hasCMov())
-    if (SDValue RV = combineIntegerAbs(N, DAG))
-      return RV;
-
   if (SDValue FPLogic = convertIntLogicToFPLogic(N, DAG, Subtarget))
     return FPLogic;
 


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