[ARM] Explicit lowering of half <-> double conversions.

If an FP_EXTEND or FP_ROUND isel dag node converts directly between
f16 and f32 when the target CPU has no instruction to do it in one go,
it has to be done in two steps instead, going via f32.

Previously, this was done implicitly, because all such CPUs had the
storage-only implementation of f16 (i.e. the only thing you can do
with one at all is to convert it to/from f32). So isel would legalize
the f16 into an f32 as soon as it saw it, by inserting an fp16_to_fp
node (or vice versa), and then the fp_extend would already be f32->f64
rather than f16->f64.

But that technique can't support a target CPU which has full f16
support but _not_ f64, such as some variants of Arm v8.1-M. So now we
provide custom lowering for FP_EXTEND and FP_ROUND, which checks
support for f16 and f64 and decides on the best thing to do given the
combination of flags it gets back.

Reviewers: dmgreen, samparker, SjoerdMeijer

Subscribers: javed.absar, kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60692

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364294 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index df07152d1767b188f931a033d2c9ce62dad4dfe0..f082c843ccd9817fb8bec47890a84a24323360ad 100644 (file)
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -768,9 +768,19 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::FP_TO_SINT, MVT::f64, Custom);
     setOperationAction(ISD::FP_TO_UINT, MVT::f64, Custom);
     setOperationAction(ISD::FP_ROUND,   MVT::f32, Custom);
+  }
+
+  if (!Subtarget->hasFP64() || !Subtarget->hasFPARMv8Base()){
     setOperationAction(ISD::FP_EXTEND,  MVT::f64, Custom);
+    setOperationAction(ISD::FP_ROUND,  MVT::f16, Custom);
   }
 
+  if (!Subtarget->hasFP16())
+    setOperationAction(ISD::FP_EXTEND,  MVT::f32, Custom);
+
+  if (!Subtarget->hasFP64())
+    setOperationAction(ISD::FP_ROUND,  MVT::f32, Custom);
+
   computeRegisterProperties(Subtarget->getRegisterInfo());
 
   // ARM does not have floating-point extending loads.
@@ -14415,27 +14425,74 @@ ARMTargetLowering::LowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const
 }
 
 SDValue ARMTargetLowering::LowerFP_EXTEND(SDValue Op, SelectionDAG &DAG) const {
-  assert(Op.getValueType() == MVT::f64 && !Subtarget->hasFP64() &&
+  SDValue SrcVal = Op.getOperand(0);
+  const unsigned DstSz = Op.getValueType().getSizeInBits();
+  const unsigned SrcSz = SrcVal.getValueType().getSizeInBits();
+  assert(DstSz > SrcSz && DstSz <= 64 && SrcSz >= 16 &&
          "Unexpected type for custom-lowering FP_EXTEND");
 
+  assert((!Subtarget->hasFP64() || !Subtarget->hasFPARMv8Base()) &&
+         "With both FP DP and 16, any FP conversion is legal!");
+
+  assert(!(DstSz == 32 && Subtarget->hasFP16()) &&
+         "With FP16, 16 to 32 conversion is legal!");
+
+  // Either we are converting from 16 -> 64, without FP16 and/or
+  // FP.double-precision or without Armv8-fp. So we must do it in two
+  // steps.
+  // Or we are converting from 32 -> 64 without fp.double-precision or 16 -> 32
+  // without FP16. So we must do a function call.
+  SDLoc Loc(Op);
   RTLIB::Libcall LC;
-  LC = RTLIB::getFPEXT(Op.getOperand(0).getValueType(), Op.getValueType());
+  if (SrcSz == 16) {
+    // Instruction from 16 -> 32
+    if (Subtarget->hasFP16())
+      SrcVal = DAG.getNode(ISD::FP_EXTEND, Loc, MVT::f32, SrcVal);
+    // Lib call from 16 -> 32
+    else {
+      LC = RTLIB::getFPEXT(MVT::f16, MVT::f32);
+      assert(LC != RTLIB::UNKNOWN_LIBCALL &&
+             "Unexpected type for custom-lowering FP_EXTEND");
+      SrcVal =
+        makeLibCall(DAG, LC, MVT::f32, SrcVal, /*isSigned*/ false, Loc).first;
+    }
+  }
 
-  SDValue SrcVal = Op.getOperand(0);
-  return makeLibCall(DAG, LC, Op.getValueType(), SrcVal, /*isSigned*/ false,
-                     SDLoc(Op)).first;
+  if (DstSz != 64)
+    return SrcVal;
+  // For sure now SrcVal is 32 bits
+  if (Subtarget->hasFP64()) // Instruction from 32 -> 64
+    return DAG.getNode(ISD::FP_EXTEND, Loc, MVT::f64, SrcVal);
+
+  LC = RTLIB::getFPEXT(MVT::f32, MVT::f64);
+  assert(LC != RTLIB::UNKNOWN_LIBCALL &&
+         "Unexpected type for custom-lowering FP_EXTEND");
+  return makeLibCall(DAG, LC, MVT::f64, SrcVal, /*isSigned*/ false, Loc).first;
 }
 
 SDValue ARMTargetLowering::LowerFP_ROUND(SDValue Op, SelectionDAG &DAG) const {
-  assert(Op.getOperand(0).getValueType() == MVT::f64 && !Subtarget->hasFP64() &&
+  SDValue SrcVal = Op.getOperand(0);
+  EVT SrcVT = SrcVal.getValueType();
+  EVT DstVT = Op.getValueType();
+  const unsigned DstSz = Op.getValueType().getSizeInBits();
+  const unsigned SrcSz = SrcVT.getSizeInBits();
+  assert(DstSz < SrcSz && SrcSz <= 64 && DstSz >= 16 &&
          "Unexpected type for custom-lowering FP_ROUND");
 
-  RTLIB::Libcall LC;
-  LC = RTLIB::getFPROUND(Op.getOperand(0).getValueType(), Op.getValueType());
+  assert((!Subtarget->hasFP64() || !Subtarget->hasFPARMv8Base()) &&
+         "With both FP DP and 16, any FP conversion is legal!");
 
-  SDValue SrcVal = Op.getOperand(0);
-  return makeLibCall(DAG, LC, Op.getValueType(), SrcVal, /*isSigned*/ false,
-                     SDLoc(Op)).first;
+  SDLoc Loc(Op);
+
+  // Instruction from 32 -> 16 if hasFP16 is valid
+  if (SrcSz == 32 && Subtarget->hasFP16())
+    return Op;
+
+  // Lib call from 32 -> 16 / 64 -> [32, 16]
+  RTLIB::Libcall LC = RTLIB::getFPROUND(SrcVT, DstVT);
+  assert(LC != RTLIB::UNKNOWN_LIBCALL &&
+         "Unexpected type for custom-lowering FP_ROUND");
+  return makeLibCall(DAG, LC, DstVT, SrcVal, /*isSigned*/ false, Loc).first;
 }
 
 void ARMTargetLowering::lowerABS(SDNode *N, SmallVectorImpl<SDValue> &Results,

diff --git a/lib/Target/ARM/ARMInstrVFP.td b/lib/Target/ARM/ARMInstrVFP.td
index af84157cda532fdd8baf57b39ec8520acce6614d..f640628394417c99c537c1c7139506f45ae8d5b8 100644 (file)
--- a/lib/Target/ARM/ARMInstrVFP.td
+++ b/lib/Target/ARM/ARMInstrVFP.td
@@ -714,8 +714,8 @@ def VCVTBHS: ASuI<0b11101, 0b11, 0b0010, 0b01, 0, (outs SPR:$Sd), (ins SPR:$Sm),
                  Requires<[HasFP16]>,
              Sched<[WriteFPCVT]>;
 
-def : FullFP16Pat<(f32 (fpextend HPR:$Sm)),
-                  (VCVTBHS (COPY_TO_REGCLASS HPR:$Sm, SPR))>;
+def : FP16Pat<(f32 (fpextend HPR:$Sm)),
+              (VCVTBHS (COPY_TO_REGCLASS HPR:$Sm, SPR))>;
 def : FP16Pat<(f16_to_fp GPR:$a),
               (VCVTBHS (COPY_TO_REGCLASS GPR:$a, SPR))>;
 
@@ -725,8 +725,8 @@ def VCVTBSH: ASuI<0b11101, 0b11, 0b0011, 0b01, 0, (outs SPR:$Sd), (ins SPR:$Sm),
                  Requires<[HasFP16]>,
              Sched<[WriteFPCVT]>;
 
-def : FullFP16Pat<(f16 (fpround SPR:$Sm)),
-                  (COPY_TO_REGCLASS (VCVTBSH SPR:$Sm), HPR)>;
+def : FP16Pat<(f16 (fpround SPR:$Sm)),
+              (COPY_TO_REGCLASS (VCVTBSH SPR:$Sm), HPR)>;
 def : FP16Pat<(fp_to_f16 SPR:$a),
               (i32 (COPY_TO_REGCLASS (VCVTBSH SPR:$a), GPR))>;
 

diff --git a/test/CodeGen/ARM/half.ll b/test/CodeGen/ARM/half.ll
index 6759a0576e75c21363db10f7e4e585693ae88539..21ac4f927c6ce3f61aebfa680cc6ec16f8dac986 100644 (file)
--- a/test/CodeGen/ARM/half.ll
+++ b/test/CodeGen/ARM/half.ll
@@ -3,6 +3,10 @@
 ; RUN: llc < %s -mtriple=thumbv8-apple-ios7.0 | FileCheck %s --check-prefix=CHECK  --check-prefix=CHECK-V8
 ; RUN: llc < %s -mtriple=armv8r-none-none-eabi | FileCheck %s --check-prefix=CHECK  --check-prefix=CHECK-V8
 ; RUN: llc < %s -mtriple=armv8r-none-none-eabi -mattr=-fp64 | FileCheck %s --check-prefix=CHECK  --check-prefix=CHECK-V8-SP
+; RUN: llc < %s -mtriple=armv8.1m-none-none-eabi -mattr=+fp-armv8 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V8
+; RUN: llc < %s -mtriple=armv8.1m-none-none-eabi -mattr=+fp-armv8,-fp64 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V8-SP
+; RUN: llc < %s -mtriple=armv8.1m-none-none-eabi -mattr=+mve.fp,+fp64 | FileCheck %s --check-prefix=CHECK-V8
+; RUN: llc < %s -mtriple=armv8.1m-none-none-eabi -mattr=+mve.fp | FileCheck %s --check-prefix=CHECK-V8-SP
 
 define void @test_load_store(half* %in, half* %out) {
 ; CHECK-LABEL: test_load_store: