https://bugs.llvm.org/show_bug.cgi?id=45610
Bug ID: 45610
Summary: Misoptimizations caused by "[ARM] Fix conditions for
lowering to S[LR]I"
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: AArch64
Assignee: unassignedb...@nondot.org
Reporter: mar...@martin.st
CC: arnaud.degrandmai...@arm.com,
llvm-bugs@lists.llvm.org, smithp...@googlemail.com,
ties.st...@arm.com
This commit, "[ARM] Fix conditions for lowering to S[LR]I"
https://reviews.llvm.org/D77387, causes misoptimizations to the following
function:
$ cat test.c
void rgb16to24(const unsigned char *src, unsigned char *dst, int src_size) {
unsigned char *d = dst;
const unsigned short *s = (const unsigned short *)src;
const unsigned short *end = s + src_size / 2;
while (s < end) {
unsigned short bgr = *s++;
*d++ = ((bgr&0xF800)>>8) | ((bgr&0xF800)>>13);
*d++ = ((bgr&0x07E0)>>3) | ((bgr&0x07E0)>> 9);
*d++ = ((bgr&0x001F)<<3) | ((bgr&0x001F)>> 2);
}
}
Compiled e.g. like this:
$ clang -target aarch64-linux-gnu -S -O3 test.c -o test.s
I haven't pinpointed which bit of the change in the output is wrong, but
running the function as part of a testsuite points it out as incorrect.
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