Canonicalize (srl (bswap x), 16) to (rotr (bswap x), 16) if the high 16 bits

of x are zero. This optimizes rev + lsr 16 to rev16.

rdar://10750814

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151230 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index b0960c5baa3061b3379fe062938196f8fa8d7f27..8a02162665f0e40b9ff4ff621d70f8c2f7a6b1bb 100644 (file)
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -800,6 +800,9 @@ ARMTargetLowering::ARMTargetLowering(TargetMachine &TM)
     setTargetDAGCombine(ISD::XOR);
   }
 
+  if (Subtarget->hasV6Ops())
+    setTargetDAGCombine(ISD::SRL);
+
   setStackPointerRegisterToSaveRestore(ARM::SP);
 
   if (TM.Options.UseSoftFloat || Subtarget->isThumb1Only() ||
@@ -7964,6 +7967,18 @@ static SDValue PerformIntrinsicCombine(SDNode *N, SelectionDAG &DAG) {
 static SDValue PerformShiftCombine(SDNode *N, SelectionDAG &DAG,
                                    const ARMSubtarget *ST) {
   EVT VT = N->getValueType(0);
+  if (N->getOpcode() == ISD::SRL && VT == MVT::i32 && ST->hasV6Ops()) {
+    // Canonicalize (srl (bswap x), 16) to (rotr (bswap x), 16) if the high
+    // 16-bits of x is zero. This optimizes rev + lsr 16 to rev16.
+    SDValue N1 = N->getOperand(1);
+    if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N1)) {
+      SDValue N0 = N->getOperand(0);
+      if (C->getZExtValue() == 16 && N0.getOpcode() == ISD::BSWAP &&
+          DAG.MaskedValueIsZero(N0.getOperand(0),
+                                APInt::getHighBitsSet(32, 16)))
+        return DAG.getNode(ISD::ROTR, N->getDebugLoc(), VT, N0, N1);
+    }
+  }
 
   // Nothing to be done for scalar shifts.
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();

diff --git a/test/CodeGen/ARM/rev.ll b/test/CodeGen/ARM/rev.ll
index ea44c28fb707c763288933e9f14be87f35d48da1..6bb67431198ab00f4e174c1b612a942c0baf91df 100644 (file)
--- a/test/CodeGen/ARM/rev.ll
+++ b/test/CodeGen/ARM/rev.ll
@@ -112,11 +112,11 @@ entry:
   ret i32 %conv3
 }
 
+; rdar://10750814
 define zeroext i16 @test9(i16 zeroext %v) nounwind readnone {
 entry:
 ; CHECK: test9
-; CHECK: rev r0, r0
-; CHECK: lsr r0, r0, #16
+; CHECK: rev16 r0, r0
   %conv = zext i16 %v to i32
   %shr4 = lshr i32 %conv, 8
   %shl = shl nuw nsw i32 %conv, 8