I probably wouldn't worry about the cost of LoopInfo; it's relatively
cheap to compute. But if you're really concerned, you can run your pass
after a pass which preserves LoopInfo (so it's free because it was
already computed). Or you can stick your code into an existing pass
which requires LoopInfo anyway, like LoopIdiomRecognize.
-Eli
On 4/23/2018 3:37 PM, Anom LLVM wrote:
> Thanks for the answer Eli.
>
> I think I was a little too vague in my question. The program has the
> following structure:
> void foo() {
> bar();
> }
>
> void bar() {
> for (..) {
> __builtin_compute()
> }
> }
>
> We would like to use scalar evolution + loopinfowrapperpass inside
> instcombine only if __builtin_compute is present. instcombine can
> convert the loop into a single builtin ie.
>
> void bar() {
> __builtin_wide_compute();
> }
>
> When the inliner runs on foo(), we want bar() to already have the
> transformation to reflect the cost of the inlining decision more
> accurately.
>
> I do see that scalar evolution is a lazy but loopwrapinfopass is not.
> Is there a way to run these two analysis passes conditionally before
> inlining?
>
> Thanks,
>
> Stan
>
>
>
>
>
>
> On Fri, Apr 20, 2018 at 1:55 PM, Friedman, Eli
> <efriedma at codeaurora.org <mailto:efriedma at codeaurora.org>> wrote:
>
> On 4/19/2018 1:57 PM, Anom LLVM via llvm-dev wrote:
>
> Hi,
>
> I have pass phase ordering question.
>
> I am interested in performing a transformation that matches
> several LLVM IR instructions and converts them to a single
> builtin. This sort of transformation must occur prior to
> inlining because inlining needs to analyze cost of the
> builtin. However, the LLVM IR -> builtin transformation
> requires scalar evolution which typically doesn't run until
> after the inliner.
>
>
> This isn't right, or at least, not the complete picture; loop
> optimization passes run interleaved with the inliner. (Try looking
> at the output of "-debug-pass=Executions" to see exactly what's
> happening.)
>
> My question is, is there a way to run scalar evolution
> conditionally prior to inlining? I'd like to leave compile
> time unaffected if my code doesn't contain any of these builtins.
>
>
> ScalarEvolution is lazy, so it's essentially free if you don't
> query it.
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
>
--
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
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