https://llvm.org/bugs/show_bug.cgi?id=31930
Bug ID: 31930
Summary: Optimization of loop via loop peeling does not occur
for float and double
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: drr...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Consider:
float f(float x[]) {
float p = 1.0;
for (int i = 0; i < 960; i++)
p += 1;
return p;
}
When compiled with -march=core-avx2 -O3 -ffast-math the assembly loops round
adding until it gets to 961.
However:
int f(int x[]) {
int p = 1;
for (int i = 0; i < 960; i++)
p += 1;
return p;
}
gives:
f: # @f
mov eax, 961
ret
I don't know how hard it would be to add the same optimization for floats and
double.
As a side note, there are in fact a number of interesting details with the
first (float) loop. First, if we reduce the i < 960 limit to i < 959 the loop
is optimized out. Second if we change the type to 'double' this upper limit
goes down to i < 479. My guess is that this corresponds to an unpeeling cost
model that is incorporated into the compiler.
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