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Improve branch optimizer around implied relops #95234

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merged 32 commits into from
Jan 2, 2024

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EgorBo
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@EgorBo EgorBo commented Nov 25, 2023

Should help with cases like:

void Test(int x)
{
    if (x > 100)
        if (x > 10) // always true
            Console.WriteLine();
}
; Method Program:Test(int):this (FullOpts)
       sub      rsp, 40
       cmp      edx, 100
       jle      SHORT G_M52364_IG04
-      cmp      edx, 10
-      jle      SHORT G_M52364_IG04
       call     [System.Console:WriteLine()]
G_M52364_IG04:
       nop      
       add      rsp, 40
       ret      
-; Total bytes of code: 26
+; Total bytes of code: 21

Ideally, it should be done in "redundant branch opt" phase, but it seems to be way more complicated so at least let's have it in assertprop for now: EgorBo@cdbaac0

@dotnet-issue-labeler dotnet-issue-labeler bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Nov 25, 2023
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Issue Details

Should help with cases like:

void Test(int x)
{
    if (x > 100)
        if (x > 10) // always true
            Console.WriteLine();
}

Ideally, it should be done in "redundant branch opt" phase, but it seems to be way more complicated so at least let's have it in assertprop for now.

Author: EgorBo
Assignees: EgorBo
Labels:

area-CodeGen-coreclr

Milestone: -

@EgorBo EgorBo changed the title Optimize "implied relops" in assertprop Improve branch optimizer around implied relops Nov 30, 2023
@EgorBo EgorBo marked this pull request as ready for review November 30, 2023 18:48
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EgorBo commented Nov 30, 2023

/azp run runtime-coreclr outerloop, runtime-coreclr jitstress, Fuzzlyn

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Azure Pipelines successfully started running 3 pipeline(s).

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EgorBo commented Nov 30, 2023

PTAL @AndyAyersMS @dotnet/jit-contrib

Diffs (not too big but I have some follow-up ideas how to extend them)

// BB4:
// return;

// Check whether the dominating compare being "false" implies the dominated compare is known
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The reversal/negation here is a bit tricky, but I think I follow it.

Seems like there's a complementary case where you don't negate the upper relop and then may instead have canInferFromTrue abilities?

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Yeah, basically there are two cases:

canInferFromFalse:

if (x > 100)
{
    if (x > 10)
    {
        ...
    }
}

canInferFromTrue:

if (x > 100)
{
    ...
}
if (x > 10)
{
    ...
}

I'll check separately the 2nd case (last I tried it added very little diffs)

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(not too big but I have some follow-up ideas how to extend them

How many of those diffs represent places code itself should be cleaned up? Like your example.

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EgorBo commented Dec 1, 2023

(not too big but I have some follow-up ideas how to extend them

How many of those diffs represent places code itself should be cleaned up? Like your example.

I inspected a few diffs and they were inlining-related so I wasn't able to find an obvious case that can be cleaned up in C#

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EgorBo commented Dec 1, 2023

Hm.. arm failures look related and they're floating point related... soft floats?

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EgorBo commented Dec 28, 2023

Since the last review I found a small bug - I replaced ssize_t with target_ssize_t (Linux arm failed on CI and it was the only target where we generate R2R'd code for corelib using 64bit jit for it via crosscompilation).

@EgorBo EgorBo merged commit 7c8b2c8 into dotnet:main Jan 2, 2024
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@EgorBo EgorBo deleted the implied-relop-assertprop branch January 2, 2024 21:13
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4 participants