[llvm-dev] New register class and patterns
Matt Arsenault via llvm-dev
llvm-dev at lists.llvm.org
Fri Feb 5 11:21:01 PST 2016
On 02/04/2016 11:41 AM, Rail Shafigulin wrote:
> Does LLVM make an assumption that there is an implicit register output
> if there are no outputs given to the pattern? I'm also curious about
> how did LLVM know that an output of this instruction was setting a
> flag in a special purpose register rather than a GPR? When I look at
> the DAG pattern for the instruction, (Escalasetflag (i32 GPR:$rA),
> immSExt16:$imm, Cond), I can't find anything saying that it sets a
> flag in the special purpose register.
No, this would have to be a void side effecting instruction which is a
bit different. The flag register is an implicit register added to the
selected MachineInstr's operands.
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