https://bugs.llvm.org/show_bug.cgi?id=43580
Bug ID: 43580
Summary: Slow code generated by Clang for 525.x264_r-like loop
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Pattern:
typedef signed char schar;
void foo (schar *__restrict a, schar *__restrict b,
schar *__restrict c, int n, int step)
{
for (int j = 0; j < n; ++j)
{
for (int i = 0; i < 16; ++i)
a[i] = (b[i] + c[i]) >> 1;
a += step;
b += step;
c += step;
}
}
Current codegen:
https://godbolt.org/z/0Lo66v
Clang generates 2x slower code than icc/gcc.
Microbenchmark:
https://pastebin.com/rECq65sa
Clang SVN -O3 0m5,619s
ICC 19 -O3 0m2,525s
GCC SVN -O3 0m2,432s
With -march=haswell
Clang SVN 0m3,540s
ICC 19 0m1,892s
GCC SVN 0m2,608s
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