Summary:
Prevously assembler parsed all literals as either 32-bit integers or 32-bit floating-point values. Because of this we couldn't support f64 literals.
E.g. in instruction "v_fract_f64 v[0:1], 0.5", literal 0.5 was encoded as 32-bit literal 0x3f000000, which is incorrect and will be interpreted as 3.0517578125E-5 instead of 0.5. Correct encoding is inline constant 240 (optimal) or 32-bit literal 0x3FE00000 at least.
With this change the way immediate literals are parsed is changed. All literals are always parsed as 64-bit values either integer or floating-point. Then we convert parsed literals to correct form based on information about type of operand parsed (was literal floating or binary) and type of expected instruction operands (is this f32/64 or b32/64 instruction).
Here are rules how we convert literals:
- We parsed fp literal:
- Instruction expects 64-bit operand:
- If parsed literal is inlinable (e.g. v_fract_f64_e32 v[0:1], 0.5)
- then we do nothing this literal
- Else if literal is not-inlinable but instruction requires to inline it (e.g. this is e64 encoding, v_fract_f64_e64 v[0:1], 1.5)
- report error
- Else literal is not-inlinable but we can encode it as additional 32-bit literal constant
- If instruction expect fp operand type (f64)
- Check if low 32 bits of literal are zeroes (e.g. v_fract_f64 v[0:1], 1.5)
- If so then do nothing
- Else (e.g. v_fract_f64 v[0:1], 3.1415)
- report warning that low 32 bits will be set to zeroes and precision will be lost
- set low 32 bits of literal to zeroes
- Instruction expects integer operand type (e.g. s_mov_b64_e32 s[0:1], 1.5)
- report error as it is unclear how to encode this literal
- Instruction expects 32-bit operand:
- Convert parsed 64 bit fp literal to 32 bit fp. Allow lose of precision but not overflow or underflow
- Is this literal inlinable and are we required to inline literal (e.g. v_trunc_f32_e64 v0, 0.5)
- do nothing
- Else report error
- Do nothing. We can encode any other 32-bit fp literal (e.g. v_trunc_f32 v0, 10000000.0)
- Parsed binary literal:
- Is this literal inlinable (e.g. v_trunc_f32_e32 v0, 35)
- do nothing
- Else, are we required to inline this literal (e.g. v_trunc_f32_e64 v0, 35)
- report error
- Else, literal is not-inlinable and we are not required to inline it
- Are high 32 bit of literal zeroes or same as sign bit (32 bit)
- do nothing (e.g. v_trunc_f32 v0, 0xdeadbeef)
- Else
- report error (e.g. v_trunc_f32 v0, 0x123456789abcdef0)
For this change it is required that we know operand types of instruction (are they f32/64 or b32/64). I added several new register operands (they extend previous register operands) and set operand types to corresponding types:
'''
enum OperandType {
OPERAND_REG_IMM32_INT,
OPERAND_REG_IMM32_FP,
OPERAND_REG_INLINE_C_INT,
OPERAND_REG_INLINE_C_FP,
}
'''
This is not working yet:
- Several tests are failing
- Problems with predicate methods for inline immediates
- LLVM generated assembler parts try to select e64 encoding before e32.
More changes are required for several AsmOperands.
Reviewers: vpykhtin, tstellarAMD
Subscribers: arsenm, kzhuravl, artem.tamazov
Differential Revision: https://reviews.llvm.org/D22922
llvm-svn: 281050
Sam Kolton