Propagate assertions through Exception handlers.

[sandreenko]

for such C# code:

int[] array = new int[100];
int i = 0;
while (i < 100)
{
    try
    {
    }
    catch (NullReferenceException arg_16_0)
    {
        array[i] = i; <- that bounds check can't be eliminated without that change.
    }
    array[i] = i; <- that bounds check can't be eliminated without that change.

    i++;
}

without that change, we were not able to eliminate bounds/null checks in/after exception handler blocks.

The initial restriction was added because we can jump to the exception handler from any instruction in the try region. So we set bbAssertionIn to empty set to guarantee that we don't propagate something that is true only for some points in the try block.

With that change, we calculate assertions that are always valid in the try block as firstTryBlock->bbAssertionIn & lastTryBlock->bbAssertionOut.

We always create unique assertions so if we have smth like:

null check V01 <- <- assertion01 is created
try 
{ <- assertion01 is alive
    V01 = smth <- assertion01 is killed
    null check V01 <- assertion02 is created
} <- assertion02 is alive
catch <- no asserion is alive, because assertion01 and assertion02 are different assertions.
{}

firstTryBlock->bbAssertionIn & lastTryBlock->bbAssertionOut will still be valid.

diffs:
System.Private.CoreLib: -114 (-0.00% of base)
21 total methods with Code Size differences (21 improved, 0 regressed), 26848 unchanged.

framework assemblies: -1111 (-0.00% of base)
207 total methods with Code Size differences (207 improved, 0 regressed), 185568 unchanged.

The improvements look like expected: we eliminate null checks and bounds checks in and after handlers.

I will improve CSE later in a separate PR because it has other pessimizationz as well.

[sandreenko]

PTAL @dotnet/jit-contrib

[CarolEidt]

Nice!

[sandreenko]

/azp list

[azure-pipelines]

CI/CD Pipelines for this repository:

• runtime-installer
• runtime-libraries
• runtime-coreclr
• runtime-coreclr outerloop
• runtime-coreclr crossgen2
• runtime-libraries outerloop
• runtime-libraries outerloop-windows
• runtime-libraries outerloop-linux
• runtime-libraries outerloop-osx

[sandreenko]

/azp run runtime-coreclr outerloop

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[sandreenko]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

Hm, @jashook do you know what I am doing wrong?
but outerloop is red anyway, so I think I will skip it here.

[jashook]

@sandreenko this is unfortunately a workflow regression that we are trying to address with Azure Dev Ops. Currently the only way to launch the pipeline is to go to https://dev.azure.com/dnceng/public/_build?definitionId=655 and manually queue.

Note that the queue branch is the same as it was for the jitstress pipelines: refs/pull/pr_number/head

[jashook]

/cc @dotnet/jit-contrib @dotnet/runtime-infrastructure

[briansull]

Optimization into catrch clauses are unlikely to improve performance measurably as we don't expect catch clauses to be executed on any hot code path. (Additionally the runtime will use thousands of cycles when dispatching into a catch)
However if this also optimizes into an (un-cloned) finally block then that would be a useful optimization to enable.

[erozenfeld]

LGTM