https://llvm.org/bugs/show_bug.cgi?id=26956
Bug ID: 26956
Summary: [SLP] Missed opportunity to generate min/max reduction
for fully unrolled loop
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Loop Optimizer
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected],
[email protected]
Classification: Unclassified
# define MAX(x,y) ((x)>(y)?(x):(y))
double arr[16];
double bar() {
double max = arr[0];
for (int i = 1; i < 16; ++i)
max = MAX(max, arr[i]);
return max;
}
Given the above code, LLVM currently fully unrolls the loop and the SLP
vectorizer is unable to vectorize the resulting code. If we replace the
constant 16 with an unknown trip count the loop vectorizer will catch this
case.
Please feel free to provide feedback as I'd like to solve this problem, but I
have no experience with the SLP vectorizer.
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