Displaying 4 results from an estimated 4 matches for "gir_copyoraddzeroreg".
2018 Jan 04
2
Canonical way to handle zero registers?
...en-erated ISel code will try to replace
> will try to replace 'G_CONSTANT s32 0' with WZR whenever the operand is
> specified as GPR32z.
>
Is this method extensible to the case of other hardwired register values?
Tracing through the code, I noticed that it seems to boil down to a
GIR_CopyOrAddZeroReg opcode, which seems like a pretty deep embedding of
the specialness of zero.
Also, IIUC, GPR32z is defining a special reg class that enables the
zero-register transformation. Defining a new reg class seems pretty
heavyweight for this; is there ever a situation where you wouldn't want the
zero-...
2018 Jan 04
0
Canonical way to handle zero registers?
...en-erated ISel code will try to replace will try to replace 'G_CONSTANT s32 0' with WZR whenever the operand is specified as GPR32z.
>
>
> Is this method extensible to the case of other hardwired register values? Tracing through the code, I noticed that it seems to boil down to a GIR_CopyOrAddZeroReg opcode, which seems like a pretty deep embedding of the specialness of zero.
At the moment, zero is hardwired since losing an AArch64 optimization was the motivating case behind adding it and the only other hardwired register I knew about was Mips's $0 but I see no reason we couldn't expan...
2018 Jan 02
0
Canonical way to handle zero registers?
Hi Sean,
Just to give the GlobalISel perspective on this, GlobalISel supports the declaration of a zero register in the register class like so:
def GPR32z : RegisterOperand<GPR32> {
let GIZeroRegister = WZR;
}
With that definition, the tablegen-erated ISel code will try to replace will try to replace 'G_CONSTANT s32 0' with WZR whenever the operand is specified as GPR32z.
>
2017 Dec 22
4
Canonical way to handle zero registers?
I looked around the codebase and didn't see anything that obviously looked
like the natural place to turn constant zero immediates into zero-registers
(i.e. registers that always return zero when read). Right now we are
expanding them in ISelLowering::LowerOperation but that seems too early.
The specific issue I'm hitting is that we have a register that reads as -1
and so when we replace