[WIP][AMDGPU] Split isInlinableLiteral16 into three and call the specific version if possible

The current implementation of `isInlinableLiteral16` assumes, a 16-bit inlinable
literal is either an i16 or a fp16. This is not always true because of bf16.
However, we can't tell fp16 and bf16 apart by just looking at the value. This
patch tries to split `isInlinableLiteral16` into three versions, i16, fp16, bf16
respectively, and call the corresponding version.

This patch is based on llvm#81282. The current status is, only two uses of original
`isInlinableLiteral16` are still there. We need to add an extra argument to indicate
the type of the operand the immediate corresponds to. This will also require the
change of the function signature of the two callers.

Author: shiltian

llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp

@@ -1927,8 +1927,12 @@ static bool isInlineableLiteralOp16(int64_t Val, MVT VT, bool HasInv2Pi) {
     return isInlinableIntLiteral(Val);
   }
 
-  // f16/v2f16 operands work correctly for all values.
-  return AMDGPU::isInlinableLiteral16(Val, HasInv2Pi);
+  if (VT.getScalarType() == MVT::f16)
+    return AMDGPU::isInlinableLiteralFP16(Val, HasInv2Pi);
+
+  assert(VT.getScalarType() == MVT::bf16);
+
+  return AMDGPU::isInlinableLiteralBF16(Val, HasInv2Pi);
 }
 
 bool AMDGPUOperand::isInlinableImm(MVT type) const {
@@ -2277,15 +2281,26 @@ void AMDGPUOperand::addLiteralImmOperand(MCInst &Inst, int64_t Val, bool ApplyMo
     return;
 
   case AMDGPU::OPERAND_REG_IMM_INT16:
-  case AMDGPU::OPERAND_REG_IMM_FP16:
-  case AMDGPU::OPERAND_REG_IMM_FP16_DEFERRED:
   case AMDGPU::OPERAND_REG_INLINE_C_INT16:
-  case AMDGPU::OPERAND_REG_INLINE_C_FP16:
   case AMDGPU::OPERAND_REG_INLINE_AC_INT16:
+    if (isSafeTruncation(Val, 16) &&
+        AMDGPU::isInlinableIntLiteral(static_cast<int16_t>(Val))) {
+      Inst.addOperand(MCOperand::createImm(Val));
+      setImmKindConst();
+      return;
+    }
+
+    Inst.addOperand(MCOperand::createImm(Val & 0xffff));
+    setImmKindLiteral();
+    return;
+
+  case AMDGPU::OPERAND_REG_INLINE_C_FP16:
+  case AMDGPU::OPERAND_REG_IMM_FP16:
+  case AMDGPU::OPERAND_REG_IMM_FP16_DEFERRED:
   case AMDGPU::OPERAND_REG_INLINE_AC_FP16:
     if (isSafeTruncation(Val, 16) &&
-        AMDGPU::isInlinableLiteral16(static_cast<int16_t>(Val),
-                                     AsmParser->hasInv2PiInlineImm())) {
+        AMDGPU::isInlinableLiteralFP16(static_cast<int16_t>(Val),
+                                       AsmParser->hasInv2PiInlineImm())) {
       Inst.addOperand(MCOperand::createImm(Val));
       setImmKindConst();
       return;
@@ -2296,12 +2311,17 @@ void AMDGPUOperand::addLiteralImmOperand(MCInst &Inst, int64_t Val, bool ApplyMo
     return;
 
   case AMDGPU::OPERAND_REG_INLINE_C_V2INT16:
+  case AMDGPU::OPERAND_REG_INLINE_AC_V2INT16: {
+    assert(isSafeTruncation(Val, 16));
+    assert(AMDGPU::isInlinableIntLiteral(static_cast<int16_t>(Val)));
+    Inst.addOperand(MCOperand::createImm(Val));
+    return;
+  }
   case AMDGPU::OPERAND_REG_INLINE_C_V2FP16:
-  case AMDGPU::OPERAND_REG_INLINE_AC_V2INT16:
   case AMDGPU::OPERAND_REG_INLINE_AC_V2FP16: {
     assert(isSafeTruncation(Val, 16));
-    assert(AMDGPU::isInlinableLiteral16(static_cast<int16_t>(Val),
-                                        AsmParser->hasInv2PiInlineImm()));
+    assert(AMDGPU::isInlinableLiteralFP16(static_cast<int16_t>(Val),
+                                          AsmParser->hasInv2PiInlineImm()));
 
     Inst.addOperand(MCOperand::createImm(Val));
     return;
@@ -3434,7 +3454,12 @@ bool AMDGPUAsmParser::isInlineConstant(const MCInst &Inst,
         OperandType == AMDGPU::OPERAND_REG_IMM_V2FP16)
       return AMDGPU::isInlinableLiteralV2F16(Val);
 
-    return AMDGPU::isInlinableLiteral16(Val, hasInv2PiInlineImm());
+    if (OperandType == AMDGPU::OPERAND_REG_IMM_FP16 ||
+        OperandType == AMDGPU::OPERAND_REG_INLINE_C_FP16 ||
+        OperandType == AMDGPU::OPERAND_REG_INLINE_AC_FP16)
+      return AMDGPU::isInlinableLiteralFP16(Val, hasInv2PiInlineImm());
+
+    llvm_unreachable("invalid operand type");
   }
   default:
     llvm_unreachable("invalid operand size");

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -4196,7 +4196,7 @@ bool SIInstrInfo::isInlineConstant(const MachineOperand &MO,
       // constants in these cases
       int16_t Trunc = static_cast<int16_t>(Imm);
       return ST.has16BitInsts() &&
-             AMDGPU::isInlinableLiteral16(Trunc, ST.hasInv2PiInlineImm());
+             AMDGPU::isInlinableLiteralFP16(Trunc, ST.hasInv2PiInlineImm());
     }
 
     return false;

llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp

@@ -2655,6 +2655,36 @@ bool isInlinableLiteral16(int16_t Literal, bool HasInv2Pi) {
          Val == 0x3118;   // 1/2pi
 }
 
+bool isInlinableLiteralFP16(int16_t Literal, bool HasInv2Pi) {
+  if (!HasInv2Pi)
+    return false;
+  uint16_t Val = static_cast<uint16_t>(Literal);
+  return Val == 0x3C00 || // 1.0
+         Val == 0xBC00 || // -1.0
+         Val == 0x3800 || // 0.5
+         Val == 0xB800 || // -0.5
+         Val == 0x4000 || // 2.0
+         Val == 0xC000 || // -2.0
+         Val == 0x4400 || // 4.0
+         Val == 0xC400 || // -4.0
+         Val == 0x3118;   // 1/2pi
+}
+
+bool isInlinableLiteralBF16(int16_t Literal, bool HasInv2Pi) {
+  if (!HasInv2Pi)
+    return false;
+  uint16_t Val = static_cast<uint16_t>(Literal);
+  return Val == 0x3F00 || // 0.5
+         Val == 0xBF00 || // -0.5
+         Val == 0x3F80 || // 1.0
+         Val == 0xBF80 || // -1.0
+         Val == 0x4000 || // 2.0
+         Val == 0xC000 || // -2.0
+         Val == 0x4080 || // 4.0
+         Val == 0xC080 || // -4.0
+         Val == 0x3E22;   // 1.0 / (2.0 * pi)
+}
+
 std::optional<unsigned> getInlineEncodingV216(bool IsFloat, uint32_t Literal) {
   // Unfortunately, the Instruction Set Architecture Reference Guide is
   // misleading about how the inline operands work for (packed) 16-bit

llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h

@@ -1359,6 +1359,12 @@ bool isInlinableLiteral64(int64_t Literal, bool HasInv2Pi);
 LLVM_READNONE
 bool isInlinableLiteral32(int32_t Literal, bool HasInv2Pi);
 
+LLVM_READNONE
+bool isInlinableLiteralFP16(int16_t Literal, bool HasInv2Pi);
+
+LLVM_READNONE
+bool isInlinableLiteralBF16(int16_t Literal, bool HasInv2Pi);
+
 LLVM_READNONE
 bool isInlinableLiteral16(int16_t Literal, bool HasInv2Pi);