Inquiry About register_operand in Non-Strict RTL
Georg-Johann Lay asks whether a register_operand in non-strict RTL can contain a REG_P register that doesn't satisfy the operand's constraint.
Georg-Johann Lay is investigating ICEs (internal compiler errors) occurring during register allocation with certain RTL test cases and asks about the validity of register_operand usage in non-strict RTL. Specifically, he questions whether a register_operand can hold a REG_P register that doesn’t meet the operand’s constraint, assuming the register meets register_operand criteria and the machine mode matches. He believes this is allowed before register allocation, with insn predicates taking precedence over insn constraints, and wants to confirm this understanding.
In Details
This question concerns the validity of register operands in RTL (Register Transfer Language) before register allocation. RTL is an intermediate representation used by GCC. Non-strict RTL refers to a state where certain constraints might not be fully enforced, particularly before register allocation has assigned concrete registers. The question concerns the interaction between insn predicates (conditions that must be true for an instruction to be valid) and insn constraints (restrictions on the type of registers that can be used).
For Context
This email asks a question about GCC's internal representation of code, called RTL (Register Transfer Language). RTL is used by the compiler to represent the program's instructions in a way that's easier to optimize. The email concerns the rules about what kind of registers can be used in RTL instructions, specifically whether a register can be used even if it doesn't perfectly match the requirements of the instruction. This is important for ensuring that the compiler generates correct code and doesn't crash.