[LLVMdev] Disable Short-Circuit Evaluation?

[Justin Holewinski]

Is there any way to disable short-circuit evaluation of expressions in
Clang/LLVM?

Let's say I have C code like the following:

bool validX = get_group_id(0) > 32;

int globalIndexY0 = get_group_id(1)*186 + 6*get_local_id(1) + 0 + 1;
bool valid0       = validX && globalIndexY0 >= 4 && globalIndexY0 < 3910;

int globalIndexY1 = get_group_id(1)*186 + 6*get_local_id(1) + 1 + 1;
bool valid1       = validX && globalIndexY1 >= 4 && globalIndexY1 < 3910;

int globalIndexY2 = get_group_id(1)*186 + 6*get_local_id(1) + 2 + 1;
bool valid2       = validX && globalIndexY2 >= 4 && globalIndexY2 < 3910;

Clang, even at -O0, is performing short-circuit evaluation of these
expressions, resulting in a fair number of branch instructions being
generated.  For most targets, this is a beneficial optimizations.  However,
for my target (PTX), it would be most beneficial to actually evaluate the
entire expression and remove the unneeded branches.  Is this possible with
current Clang/LLVM?

-- 

Thanks,

Justin Holewinski
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