On Tue, Oct 19, 2021 at 03:39:11PM +0100, Mark Rutland wrote: > On Tue, Oct 19, 2021 at 11:14:47AM +0100, Will Deacon wrote: > > > + sve_flush_live(true, vq_minus_one); > > What does the pcs say about passing bools in registers? Can we guarantee > > that false is a 64-bit zero? > Per usual rules, bits [63:8] can be arbitrary -- AAPCS64 leaves it to the callee > to extend values, with the upper bits being arbitrary, and it maps _Bool/bool > to unsigned char, which covers bits [7:0]. > So a bool false in a register is not guaranteed to be a 64-bit zero. But > since it *is* guarnateed to be either 0 or 1, we can use TBZ/TBNZ > instead of CBZ/CBNZ. Either that, or extend it to a wider type in the > function prototype. I'll change it to tbz - if we use a wider type then people will notice using true/false with it in the code.
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