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Re: [PATCH] Teach VRP to register assertions along default switch labels (PR 18046)


On 07/24/2016 11:56 AM, Andrew Pinski wrote:
On Sun, Jul 24, 2016 at 9:49 AM, Patrick Palka <patrick@parcs.ath.cx> wrote:
On Sat, Jul 23, 2016 at 9:13 PM, kugan
<kugan.vivekanandarajah@linaro.org> wrote:


On 23/07/16 05:26, Patrick Palka wrote:

This patch teaches VRP to register along a default switch label
assertions that corresponds to the anti range of each case label.


Hi Patrick,

In case of a larger switch statement with case values that cannot be
combined, you could end up with very large number of ASSERT_EXPRs in the
default basic block. I am not sure if this would have any impact on compile
time/memory usage? If that is the case you might want to punt at some
length?

Hi Kugan,

That sounds like a good idea to me.  So I gathered some info about the
number of assert_exprs inserted in the default bb during GCC bootstrap
with this patch:

Max # of asserts inserted in a default BB: 59
Median #: 2
Average #: 3.33817
Std. dev: 4.76926
95% percentile: 10

Based on the last point I guess 10 would be a good limit?


Make sure this is a parameter so someone can increase it if they want.
But 10 seems like a good default.
Agreed on both points.

jeff


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