http://llvm.org/bugs/show_bug.cgi?id=944
Summary: Unrolling loop creates register pressure
Product: libraries
Version: trunk
Platform: Macintosh
OS/Version: MacOS X
Status: NEW
Severity: normal
Priority: P2
Component: Loop Optimizer
AssignedTo: unassignedbugs at nondot.org
ReportedBy: isanbard at gmail.com
When run through the optimizer twice, the following code:
int value(uint64 b1, uint64 b2)
{
int i, j, k;
int value = 0;
for (k = 0; k < 2; k++)
for (i = 0; i < 6; i++)
for (j = 0; j < 2; j++)
if ((b2 & 0xf << (j + i * 6)) == 0xf << (j + i * 6))
value += 1000;
return value;
}
gets unrolled into two loops. However, this creates a ton of register pressure, and, as a result, many
more spills/loads are added which the code running only through the optimizer once doesn't have.
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