[ARM] Add fp16 addressing to isLegalT2AddressImmediate

[dmgreen]

Summary

The fp16 version of VLDR takes a imm8 multiplied by 2. This updates the costs to account for those, and adds extra testing (which I've just shown the diff of here). It is dependant upon hasFPRegs16 as this is what the load/store instructions require.

[samparker]

llvm/test/Analysis/CostModel/ARM/gep.ll

329

Could you add testing for around an offset of +/- 510?

[dmgreen]

llvm/test/Analysis/CostModel/ARM/gep.ll

329

These are gep offsets so all "number of units", not "bytes". Is that what you meant? It caught me out originally.

(Yes, this makes testing unaligned access harder, like an byte offset of 1, not 2)

[samparker]

LGTM.

llvm/test/Analysis/CostModel/ARM/gep.ll

329

Ah, yeah!

llvm/lib/Target/ARM/ARMISelLowering.cpp

static bool isLegalT2AddressImmediate(int64_t V, EVT VT,
   bool IsNeg = false;
   if (V < 0) {
     IsNeg = true;
     V = -V;
   }
 
   unsigned NumBytes = std::max(VT.getSizeInBits() / 8, 1U);
 
+  // half VLDR: 2 * imm8
+  if (VT.isFloatingPoint() && NumBytes == 2 && Subtarget->hasFPRegs16())
+    return isShiftedUInt<8, 1>(V);
   // VLDR and LDRD: 4 * imm8
   if ((VT.isFloatingPoint() && Subtarget->hasVFP2Base()) || NumBytes == 8)
     return isShiftedUInt<8, 2>(V);
 
   if (NumBytes == 1 || NumBytes == 2 || NumBytes == 4) {
     // + imm12 or - imm8
     if (IsNeg)
       return isUInt<8>(V);

llvm/test/Analysis/CostModel/ARM/gep.ll

 ; CHECK-V7M-FP-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a1024 = getelementptr inbounds half, half* %a, i32 1024
 ; CHECK-V7M-FP-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %am63 = getelementptr inbounds half, half* %a, i32 -63
 ; CHECK-V7M-FP-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %am64 = getelementptr inbounds half, half* %a, i32 -64
 ; CHECK-V7M-FP-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %ai = getelementptr inbounds half, half* %a, i32 %i
 ; CHECK-V7M-FP-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 ; CHECK-MVE-LABEL: 'testhalf'
 ; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %a0 = getelementptr inbounds half, half* %a, i32 0
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a1 = getelementptr inbounds half, half* %a, i32 1
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %am1 = getelementptr inbounds half, half* %a, i32 -1
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a255 = getelementptr inbounds half, half* %a, i32 255
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %a256 = getelementptr inbounds half, half* %a, i32 256
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %am255 = getelementptr inbounds half, half* %a, i32 -255
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %am256 = getelementptr inbounds half, half* %a, i32 -256
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %a1 = getelementptr inbounds half, half* %a, i32 1
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %am1 = getelementptr inbounds half, half* %a, i32 -1
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %a255 = getelementptr inbounds half, half* %a, i32 255
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a256 = getelementptr inbounds half, half* %a, i32 256
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %am255 = getelementptr inbounds half, half* %a, i32 -255
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %am256 = getelementptr inbounds half, half* %a, i32 -256
 ; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a1023 = getelementptr inbounds half, half* %a, i32 1023
 ; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a1024 = getelementptr inbounds half, half* %a, i32 1024
-; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %am63 = getelementptr inbounds half, half* %a, i32 -63
+; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %am63 = getelementptr inbounds half, half* %a, i32 -63
 ; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %am64 = getelementptr inbounds half, half* %a, i32 -64
 ; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %ai = getelementptr inbounds half, half* %a, i32 %i
 ; CHECK-MVE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 ; CHECK-T32-LABEL: 'testhalf'
 ; CHECK-T32-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %a0 = getelementptr inbounds half, half* %a, i32 0
 ; CHECK-T32-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %a1 = getelementptr inbounds half, half* %a, i32 1
 ; CHECK-T32-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %am1 = getelementptr inbounds half, half* %a, i32 -1