Notably, llvm.amdgcn.readfirstlane and llvm.amdgcn.icmp may be hoisted
out of loops or if/else branches in cases like
if (cond) {
v = readFirstInvocationARB(x);
... use v ...
} else {
v = readFirstInvocationARB(x);
... use v ...
}
===>
v = readFirstInvocationARB(x);
if (cond) {
... use v ...
} else {
... use v ...
}
The optimization barrier is a heavy hammer to stop that until LLVM
is taught the semantics of the intrinsic properly.
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Nicolai Hähnle
8b13b11f11