https://bugs.llvm.org/show_bug.cgi?id=35295
Bug ID: 35295
Summary: Potential improvement for vectorization of sub
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: serguei.kat...@azul.com
CC: llvm-bugs@lists.llvm.org
Hi,
I'm not sure that the example below is valid but still I'd like to understand
difference in vectorizer behavior for add and sub.
Let consider two following c++ functions (https://godbolt.org/g/WxjdMP):
void testAdd(signed char a[], int N, signed int k) {
for (int i = 0; i < N; i++)
a[i] += k;
}
void testSub(signed char a[], int N, signed int k) {
for (int i = 0; i < N; i++)
a[i] -= k;
}
for testAdd vectorizer is able to utilize packed byte size paddb instruction
while for sub it is not. Instead it uses psubd resulting in a big additional
code to convert vector of i8 to vector of i32 and vice versa.
I wonder whether it is possible to utilize psubb for the second case.
I noticed that both gcc and icc is able to do that...
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