More precise ranges for casts in GetRangeFromAssertions by EgorBo · Pull Request #124415 · dotnet/runtime

EgorBo · 2026-02-14T01:24:49Z

dotnet-policy-service · 2026-02-14T01:25:56Z

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Copilot

Pull request overview

This PR improves range analysis in the JIT's range check optimization pass by enabling more precise range propagation through cast operations and adding support for TYP_INT in GetRangeFromType.

Changes:

Add early range tightening based on VN type for small types in GetRangeFromAssertions (though this appears to be dead code due to VN normalization)
Change cast source type check from exact TYP_INT match to using genActualType, making the code more defensive
Add TYP_INT case to GetRangeFromType to return the full int32 range instead of Unknown

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Copilot

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The varTypeIsGC(vnType) branch was added defensively for 32-bit, where TYP_I_IMPL == TYP_INT could in theory let GC-typed VNs reach this code. In practice, all callers gate on TYP_INT and recursive sites either gate on TYP_INT or operate on results that cannot produce GC operands of an INT VN. SPMI replay (x64 aspnet/libraries/benchmarks and x86 benchmarks) shows no behavior change after removal — asmdiffs are identical at -4,708 bytes net for aspnet. If a GC VN ever does leak in, the existing assert(genActualType(vnType) == TYP_INT) will surface it cleanly. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

@jakobbotsch

Per @jakobbotsch review feedback: NOL locals can live in registers where the JIT does not insert any normalization without the cast. Retyping the LCL_VAR to its small type and dropping the cast lets codegen read the register without a normalizing load (e.g., movzx), exposing potentially undefined upper bits for register-resident NOL params. The reason morph.cpp:3230 can perform a similar retype-and-drop is that it gates on local subrange assertions, which only exist after a JIT-controlled store that normalized the bits. VN-based subrange proofs have no such guarantee — they can come from comparisons, casts, joins, or phi merges that say nothing about the physical register state. Restore the original PR behavior of skipping NOL locals entirely in the VN-based path. The local-prop path below is unchanged and still performs the safe retyping based on local assertions. Cost on benchmarks.run: +4,482 bytes vs the (unsafe) prior commit, but still -3,670 bytes net vs origin/main. SPMI replay clean on aspnet, libraries (incl. tests), benchmarks. JIT/opt/Or/IntOr disasm pattern preserved by the small-cast-on-non-LCL_VAR guard introduced earlier. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

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Reverts 0a3a858 ("Remove unreachable GC early return ...") which broke 32-bit crossgen2 of System.Private.CoreLib (Memmove and others asserting `genActualType(vnType) == TYP_INT` at rangecheck.cpp:698). Why the GC return is actually needed (and my prior analysis missed): On 32-bit targets TYP_INT/TYP_BYREF/TYP_REF are all 4 bytes, so the JIT can legally write a byref-valued expression (e.g. LCL_ADDR) into an int-typed local. The local is TYP_INT but its VN is a TYP_BYREF function such as PtrToLoc. Repro context (libraries.crossgen2 MC 146148, F# SubstHelperRaw): STORE_LCL_VAR int V06 <- LCL_ADDR int V15 # V06 has VN PtrToLoc(...) (BYREF) ...PHI int V06 across blocks $340 = PhiDef(...) NE int (LCL_VAR int V06, CNS_INT int 0) # asks for range of $340 PR dotnet#127117 (Apr 23) added PhiDef recursion in GetRangeFromAssertionsWorker; the visitor walks reaching VNs of the phi, and on 32-bit one of them can be the BYREF PtrToLoc VN even though the public caller passed an int-typed tree. The pre-existing GC early-return guard catches exactly this case; the explanatory comment is updated so the next reader doesn't repeat my mistake. x64 SPMI didn't catch it because TYP_BYREF (8 bytes) and TYP_INT (4 bytes) cannot alias in the same local, so `LCL_ADDR int` doesn't appear and the phi recursion never reaches a BYREF VN. Validation: x86 libraries.crossgen2 SPMI replay clean (279,521 ctx). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

EgorBo · 2026-05-11T11:44:08Z

@EgorBot -arm -amd

using BenchmarkDotNet.Attributes;

public class Benchmarks
{
    private byte b = 42;

    [Benchmark]
    public string ByteToString() => b.ToString();
}

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EgorBo · 2026-05-12T09:58:49Z

I think this is ready, PTAL @jakobbotsch @dotnet/jit-contrib
Some nice diffs

An example of what it folds:

runtime/src/libraries/System.Private.CoreLib/src/System/Number.Formatting.cs

Lines 1934 to 1941 in 7900769

    
           internal static string UInt32ToDecStr(uint value) 
        
           { 
        
               // For small numbers, consult a lazily-populated cache. 
        
               if (value < SmallNumberCacheLength) 
        
               { 
        
                   return UInt32ToDecStrForKnownSmallNumber(value); 
        
               }

When Byte.cs pass itself on its ToString() we can fold the value < 300 check

EgorBo · 2026-05-12T12:33:04Z

/ba-g timeouts

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Cannot find 'arm64-v8a' device dotnet/dnceng#2284

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Unable to pull image from mcr.microsoft.com #117164

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cleanup

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EgorBo force-pushed the precise-cast-ranges branch from 2704ba3 to e492c87 Compare February 14, 2026 18:54

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EgorBo marked this pull request as ready for review February 14, 2026 21:17

EgorBo added 2 commits February 14, 2026 22:19

Update assertionprop.cpp

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Update assertionprop.cpp

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MsQuic fails with QUIC_STATUS_OUT_OF_MEMORY on AzureLinux #123216

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Merge branch 'main' into precise-cast-ranges

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EgorBo force-pushed the precise-cast-ranges branch from 6546d64 to a0cbca9 Compare May 10, 2026 21:12

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Comment thread src/coreclr/jit/assertionprop.cpp Outdated

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This was referenced May 11, 2026

slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

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The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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Merge branch 'main' into precise-cast-ranges

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Benchmarks for dotnet/runtime#124415 (for @EgorBo) EgorBot/Benchmarks#199

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Merge branch 'main' into precise-cast-ranges

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Comment thread src/coreclr/jit/rangecheck.cpp

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Comment thread src/coreclr/jit/assertionprop.cpp

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EgorBo merged commit ccc1b27 into dotnet:main May 12, 2026
129 of 139 checks passed

EgorBo deleted the precise-cast-ranges branch May 12, 2026 12:33

saucecontrol mentioned this pull request May 12, 2026

JIT: Range check not eliminated by cast to value known to be in range #118305

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