On Mon, 2018-11-05 at 13:13 -0800, Andrew Morton wrote: +AD4 On Mon, 5 Nov 2018 12:40:00 -0800 Bart Van Assche +ADw-bvanassche+AEA-acm.org+AD4 wrote: +AD4 +AD4 +AD4 This patch suppresses the following sparse warning: +AD4 +AD4 +AD4 +AD4 ./include/linux/slab.h:332:43: warning: dubious: x +ACY +ACE-y +AD4 +AD4 +AD4 +AD4 ... +AD4 +AD4 +AD4 +AD4 --- a/include/linux/slab.h +AD4 +AD4 +-+-+- b/include/linux/slab.h +AD4 +AD4 +AEAAQA -329,7 +-329,7 +AEAAQA static +AF8AXw-always+AF8-inline enum kmalloc+AF8-cache+AF8-type kmalloc+AF8-type(gfp+AF8-t flags) +AD4 +AD4 +ACo If an allocation is both +AF8AXw-GFP+AF8-DMA and +AF8AXw-GFP+AF8-RECLAIMABLE, return +AD4 +AD4 +ACo KMALLOC+AF8-DMA and effectively ignore +AF8AXw-GFP+AF8-RECLAIMABLE +AD4 +AD4 +ACo-/ +AD4 +AD4 - return type+AF8-dma +- (is+AF8-reclaimable +ACY +ACE-is+AF8-dma) +ACo KMALLOC+AF8-RECLAIM+ADs +AD4 +AD4 +- return type+AF8-dma +- is+AF8-reclaimable +ACo +ACE-is+AF8-dma +ACo KMALLOC+AF8-RECLAIM+ADs +AD4 +AD4 +AH0 +AD4 +AD4 +AD4 +AD4 /+ACo +AD4 +AD4 I suppose so. +AD4 +AD4 That function seems too clever for its own good :(. I wonder if these +AD4 branch-avoiding tricks are really worthwhile. >From what I have seen in gcc disassembly it seems to me like gcc uses the cmov instruction to implement e.g. the ternary operator (?:). So I think none of the cleverness in kmalloc+AF8-type() is really necessary to avoid conditional branches. I think this function would become much more readable when using a switch statement or when rewriting it as follows (untested): static +AF8AXw-always+AF8-inline enum kmalloc+AF8-cache+AF8-type kmalloc+AF8-type(gfp+AF8-t flags) +AHs - int is+AF8-dma +AD0 0+ADs - int type+AF8-dma +AD0 0+ADs - int is+AF8-reclaimable+ADs - -+ACM-ifdef CONFIG+AF8-ZONE+AF8-DMA - is+AF8-dma +AD0 +ACEAIQ(flags +ACY +AF8AXw-GFP+AF8-DMA)+ADs - type+AF8-dma +AD0 is+AF8-dma +ACo KMALLOC+AF8-DMA+ADs -+ACM-endif - - is+AF8-reclaimable +AD0 +ACEAIQ(flags +ACY +AF8AXw-GFP+AF8-RECLAIMABLE)+ADs - /+ACo +ACo If an allocation is both +AF8AXw-GFP+AF8-DMA and +AF8AXw-GFP+AF8-RECLAIMABLE, return +ACo KMALLOC+AF8-DMA and effectively ignore +AF8AXw-GFP+AF8-RECLAIMABLE +ACo-/ - return type+AF8-dma +- (is+AF8-reclaimable +ACY +ACE-is+AF8-dma) +ACo KMALLOC+AF8-RECLAIM+ADs +- static const enum kmalloc+AF8-cache+AF8-type flags+AF8-to+AF8-type+AFs-2+AF0AWw-2+AF0 +AD0 +AHs +- +AHs 0, KMALLOC+AF8-RECLAIM +AH0, +- +AHs KMALLOC+AF8-DMA, KMALLOC+AF8-DMA +AH0, +- +AH0AOw +-+ACM-ifdef CONFIG+AF8-ZONE+AF8-DMA +- bool is+AF8-dma +AD0 +ACEAIQ(flags +ACY +AF8AXw-GFP+AF8-DMA)+ADs +-+ACM-endif +- bool is+AF8-reclaimable +AD0 +ACEAIQ(flags +ACY +AF8AXw-GFP+AF8-RECLAIMABLE)+ADs +- +- return flags+AF8-to+AF8-type+AFs-is+AF8-dma+AF0AWw-is+AF8-reclaimable+AF0AOw +AH0
