[ARM] GlobalISel: Add FPR reg bank

Add a register bank for floating point values and select simple instructions
using them (add, copies from GPR).

This assumes that the hardware can cope with a single precision add (VADDS)
instruction, so the legalizer will treat G_FADD as legal and the instruction
selector will refuse to select if the hardware doesn't support it. In the future
we'll want to be more careful about this, and legalize to libcalls if we have to
use soft float.

llvm-svn: 294442

llvm/lib/Target/ARM/ARMInstructionSelector.cpp

@@ -54,9 +54,17 @@ static bool selectCopy(MachineInstr &I, const TargetInstrInfo &TII,
            DstSize <= SrcSize)) &&
          "Copy with different width?!");
 
-  assert(RegBank->getID() == ARM::GPRRegBankID && "Unsupported reg bank");
+  assert((RegBank->getID() == ARM::GPRRegBankID ||
+          RegBank->getID() == ARM::FPRRegBankID) &&
+         "Unsupported reg bank");
+
   const TargetRegisterClass *RC = &ARM::GPRRegClass;
 
+  if (RegBank->getID() == ARM::FPRRegBankID) {
+    assert(DstSize == 32 && "Only 32-bit FP values are supported");
+    RC = &ARM::SPRRegClass;
+  }
+
   // No need to constrain SrcReg. It will get constrained when
   // we hit another of its uses or its defs.
   // Copies do not have constraints.
@@ -177,6 +185,13 @@ bool ARMInstructionSelector::select(MachineInstr &I) const {
     I.setDesc(TII.get(ARM::ADDrr));
     MIB.add(predOps(ARMCC::AL)).add(condCodeOp());
     break;
+  case G_FADD:
+    if (!TII.getSubtarget().hasVFP2() ||
+        TII.getSubtarget().useNEONForSinglePrecisionFP())
+      return false;
+    I.setDesc(TII.get(ARM::VADDS));
+    MIB.add(predOps(ARMCC::AL));
+    break;
   case G_FRAME_INDEX:
     // Add 0 to the given frame index and hope it will eventually be folded into
     // the user(s).

llvm/lib/Target/ARM/ARMLegalizerInfo.cpp

@@ -48,5 +48,9 @@ ARMLegalizerInfo::ARMLegalizerInfo() {
       setAction({Op, 1, Ty}, Legal);
   }
 
+  // FIXME: This is a bit sloppy, but for now we'll just rely on the instruction
+  // selector to complain if it doesn't support floating point.
+  setAction({G_FADD, s32}, Legal);
+
   computeTables();
 }

llvm/lib/Target/ARM/ARMRegisterBankInfo.cpp

@@ -33,9 +33,11 @@ using namespace llvm;
 namespace llvm {
 namespace ARM {
 RegisterBankInfo::PartialMapping GPRPartialMapping{0, 32, GPRRegBank};
+RegisterBankInfo::PartialMapping FPRPartialMapping{0, 32, FPRRegBank};
 
 RegisterBankInfo::ValueMapping ValueMappings[] = {
-    {&GPRPartialMapping, 1}, {&GPRPartialMapping, 1}, {&GPRPartialMapping, 1}};
+    {&GPRPartialMapping, 1}, {&GPRPartialMapping, 1}, {&GPRPartialMapping, 1},
+    {&FPRPartialMapping, 1}, {&FPRPartialMapping, 1}, {&FPRPartialMapping, 1}};
 } // end namespace arm
 } // end namespace llvm
 
@@ -82,6 +84,9 @@ const RegisterBank &ARMRegisterBankInfo::getRegBankFromRegClass(
   case GPRnopcRegClassID:
   case tGPR_and_tcGPRRegClassID:
     return getRegBank(ARM::GPRRegBankID);
+  case SPR_8RegClassID:
+  case SPRRegClassID:
+    return getRegBank(ARM::FPRRegBankID);
   default:
     llvm_unreachable("Unsupported register kind");
   }
@@ -115,6 +120,9 @@ ARMRegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     // the real world we would use different mappings.
     OperandsMapping = &ARM::ValueMappings[0];
     break;
+  case G_FADD:
+    OperandsMapping = &ARM::ValueMappings[3];
+    break;
   case G_FRAME_INDEX:
     OperandsMapping = getOperandsMapping({&ARM::ValueMappings[0], nullptr});
     break;

llvm/lib/Target/ARM/ARMRegisterBanks.td

@@ -11,3 +11,4 @@
 //===----------------------------------------------------------------------===//
 
 def GPRRegBank : RegisterBank<"GPRB", [GPR, GPRwithAPSR]>;
+def FPRRegBank : RegisterBank<"FPRB", [SPR]>;

llvm/test/CodeGen/ARM/GlobalISel/arm-instruction-select.mir

@@ -9,7 +9,11 @@
   define void @test_add_s16() { ret void }
   define void @test_add_s32() { ret void }
 
+  define void @test_fadd_s32() #0 { ret void }
+
   define void @test_load_from_stack() { ret void }
+
+  attributes #0 = { "target-features"="+vfp2" }
 ...
 ---
 name:            test_zext_s1
@@ -217,6 +221,39 @@ body:             |
     ; CHECK: BX_RET 14, _, implicit %r0
 ...
 ---
+name:            test_fadd_s32
+# CHECK-LABEL: name: test_fadd_s32
+legalized:       true
+regBankSelected: true
+selected:        false
+# CHECK: selected: true
+registers:
+  - { id: 0, class: fprb }
+  - { id: 1, class: fprb }
+  - { id: 2, class: fprb }
+# CHECK: id: 0, class: spr
+# CHECK: id: 1, class: spr
+# CHECK: id: 2, class: spr
+body:             |
+  bb.0:
+    liveins: %s0, %s1
+
+    %0(s32) = COPY %s0
+    ; CHECK: [[VREGX:%[0-9]+]] = COPY %s0
+
+    %1(s32) = COPY %s1
+    ; CHECK: [[VREGY:%[0-9]+]] = COPY %s1
+
+    %2(s32) = G_FADD %0, %1
+    ; CHECK: [[VREGSUM:%[0-9]+]] = VADDS [[VREGX]], [[VREGY]], 14, _
+
+    %s0 = COPY %2(s32)
+    ; CHECK: %s0 = COPY [[VREGSUM]]
+
+    BX_RET 14, _, implicit %s0
+    ; CHECK: BX_RET 14, _, implicit %s0
+...
+---
 name:            test_load_from_stack
 # CHECK-LABEL: name: test_load_from_stack
 legalized:       true

llvm/test/CodeGen/ARM/GlobalISel/arm-legalizer.mir

@@ -9,6 +9,8 @@
 
   define void @test_load_from_stack() { ret void }
   define void @test_legal_loads() { ret void }
+
+  define void @test_fadd_s32() { ret void }
 ...
 ---
 name:            test_sext_s8
@@ -190,3 +192,28 @@ body:             |
     %5(p0)  = G_LOAD %0(p0)
     BX_RET 14, _
 ...
+---
+name:            test_fadd_s32
+# CHECK-LABEL: name: test_fadd_s32
+legalized:       false
+# CHECK: legalized: true
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: _ }
+  - { id: 1, class: _ }
+  - { id: 2, class: _ }
+body:             |
+  bb.0:
+    liveins: %r0, %r1
+
+    %0(s32) = COPY %r0
+    %1(s32) = COPY %r1
+    %2(s32) = G_FADD %0, %1
+    ; G_FADD with s32 is legal, so we should find it unchanged in the output
+    ; CHECK: {{%[0-9]+}}(s32) = G_FADD {{%[0-9]+, %[0-9]+}}
+    %r0 = COPY %2(s32)
+    BX_RET 14, _, implicit %r0
+
+...

llvm/test/CodeGen/ARM/GlobalISel/arm-regbankselect.mir

@@ -6,6 +6,8 @@
   define void @test_add_s1() { ret void }
 
   define void @test_loads() { ret void }
+
+  define void @test_fadd_s32() { ret void }
 ...
 ---
 name:            test_add_s32
@@ -144,3 +146,29 @@ body:             |
     BX_RET 14, _, implicit %r0
 
 ...
+---
+name:            test_fadd_s32
+# CHECK-LABEL: name: test_fadd_s32
+legalized:       true
+regBankSelected: false
+selected:        false
+# CHECK: registers:
+# CHECK: - { id: 0, class: fprb }
+# CHECK: - { id: 1, class: fprb }
+# CHECK: - { id: 2, class: fprb }
+
+registers:
+  - { id: 0, class: _ }
+  - { id: 1, class: _ }
+  - { id: 2, class: _ }
+body:             |
+  bb.0:
+    liveins: %r0, %r1
+
+    %0(s32) = COPY %s0
+    %1(s32) = COPY %s1
+    %2(s32) = G_FADD %0, %1
+    %s0 = COPY %2(s32)
+    BX_RET 14, _, implicit %r0
+
+...