http://llvm.org/bugs/show_bug.cgi?id=9402
Summary: "warning: shift count >= width of type" for
unreachable expression
Product: clang
Version: trunk
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P
Component: Frontend
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
$ cat test.c
int main() {
unsigned long long c = 1 ? ~0ULL : (1ULL<<64)-1;
return c;
}
$ gcc -c test.c
$
$ clang -c test.c
test.c:2:42: warning: shift count >= width of type
unsigned long long c = 1 ? ~0ULL : (1ULL<<64)-1;
^ ~~
1 warning generated.
$
When building linux kernel, build log is full of messages like:
include/linux/dma-mapping.h:55:54: note: instantiated from:
#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
^ ~~~
drivers/ata/ahci.c:667:42: warning: shift count >= width of type
rc = pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(64));
^~~~~~~~~~~~~~~~
all values in DMA_BIT_MASK macro are compile-time constants and the unreachable
case can be eliminated without a warning.
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