[PATCH] D152911: [PowerPC] Remove extend between shift and and

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai created this revision.
nemanjai added reviewers: qiongsiwu, stefanp, PowerPC.
Herald added subscribers: shchenz, kbarton, hiraditya.
Herald added a project: All.
nemanjai requested review of this revision.
Herald added a project: LLVM.

The SDAG will sometimes insert an extend between the shift and an `and (immediate)` even though the immediate is narrower than the narrow size. This does not allow us to produce a rotate instruction (such as `rlwinm`).
This patch just adds a combine to move the extend onto the `and`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D152911

Files:
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/test/CodeGen/PowerPC/and-extend-combine.ll


Index: llvm/test/CodeGen/PowerPC/and-extend-combine.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/PowerPC/and-extend-combine.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 2
+; RUN: llc < %s -mtriple=powerpc64le-unknown-unknown -ppc-asm-full-reg-names \
+; RUN:   -mcpu=pwr8 -verify-machineinstrs | FileCheck %s
+define dso_local ptr @foo(i32 noundef zeroext %arg, ptr nocapture noundef readonly %arg1, ptr noundef writeonly %arg2) local_unnamed_addr {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0: # %bb
+; CHECK-NEXT:    rlwinm r3, r3, 31, 17, 28
+; CHECK-NEXT:    ldx r4, r4, r3
+; CHECK-NEXT:    clrldi r3, r4, 56
+; CHECK-NEXT:    add r3, r5, r3
+; CHECK-NEXT:    std r4, 0(r5)
+; CHECK-NEXT:    blr
+bb:
+  %i = lshr i32 %arg, 1
+  %i3 = and i32 %i, 32760
+  %i4 = zext i32 %i3 to i64
+  %i5 = getelementptr inbounds i8, ptr %arg1, i64 %i4
+  %i6 = load i64, ptr %i5, align 8
+  %i7 = and i64 %i6, 255
+  store i64 %i6, ptr %arg2, align 8
+  %i8 = getelementptr inbounds i8, ptr %arg2, i64 %i7
+  ret ptr %i8
+}
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1380,8 +1380,8 @@
   setStackPointerRegisterToSaveRestore(isPPC64 ? PPC::X1 : PPC::R1);
 
   // We have target-specific dag combine patterns for the following nodes:
-  setTargetDAGCombine({ISD::ADD, ISD::SHL, ISD::SRA, ISD::SRL, ISD::MUL,
-                       ISD::FMA, ISD::SINT_TO_FP, ISD::BUILD_VECTOR});
+  setTargetDAGCombine({ISD::AND, ISD::ADD, ISD::SHL, ISD::SRA, ISD::SRL,
+                       ISD::MUL, ISD::FMA, ISD::SINT_TO_FP, ISD::BUILD_VECTOR});
   if (Subtarget.hasFPCVT())
     setTargetDAGCombine(ISD::UINT_TO_FP);
   setTargetDAGCombine({ISD::LOAD, ISD::STORE, ISD::BR_CC});
@@ -15466,6 +15466,31 @@
   default: break;
   case ISD::ADD:
     return combineADD(N, DCI);
+  case ISD::AND: {
+    // We don't want (and (zext (shift...)), C) if C fits in the width of the
+    // original input as that will prevent us from selecting optimal rotates.
+    SDValue Op1 = N->getOperand(0);
+    SDValue Op2 = N->getOperand(1);
+    if ((Op1.getOpcode() != ISD::ZERO_EXTEND &&
+         Op1.getOpcode() != ISD::ANY_EXTEND) ||
+        !isa<ConstantSDNode>(Op2))
+      break;
+    SDValue NarrowOp = Op1.getOperand(0);
+    if (NarrowOp.getOpcode() != ISD::SHL && NarrowOp.getOpcode() != ISD::SRL &&
+        NarrowOp.getOpcode() != ISD::ROTL &&
+        NarrowOp.getOpcode() != ISD::ROTR &&
+        NarrowOp.getOpcode() != ISD::FSHL && NarrowOp.getOpcode() != ISD::FSHR)
+      break;
+
+    uint64_t Imm = cast<ConstantSDNode>(Op2)->getZExtValue();
+    EVT NarrowVT = NarrowOp.getValueType();
+    // Make sure that the constant is narrow enough to fit in the narrow type.
+    if (Imm >= maxUIntN(NarrowVT.getSizeInBits()))
+      break;
+    SDValue ConstOp = DAG.getConstant(Imm, dl, NarrowVT);
+    SDValue NarrowAnd = DAG.getNode(ISD::AND, dl, NarrowVT, NarrowOp, ConstOp);
+    return DAG.getAnyExtOrTrunc(NarrowAnd, dl, N->getValueType(0));
+  }
   case ISD::SHL:
     return combineSHL(N, DCI);
   case ISD::SRA:


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