JIT: Fix Compiler::printfAlloc for long strings

[jakobbotsch]

#116074 (comment)

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[jakobbotsch]

PTAL @dotnet/jit-contrib

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Pull Request Overview

This PR fixes an issue in Compiler::printfAlloc to ensure it correctly handles long strings by accurately calculating the required buffer size and then properly formatting the output.

• Utilizes _vscprintf to determine the correct buffer size.
• Reinitializes the va_list to correctly pass arguments to vsprintf_s.

Comments suppressed due to low confidence (2)

src/coreclr/jit/compiler.cpp:10597

• [nitpick] Consider renaming the variable 'result' to 'writtenCount' (or a similar name) to more clearly differentiate it from 'count', which represents the computed required size.

int result = vsprintf_s(resultStr, count + 1, format, args);

src/coreclr/jit/compiler.cpp:10596

• [nitpick] It may be useful to add a comment explaining why va_start is called a second time to reinitialize the va_list for vsprintf_s, clarifying the two-pass approach for future maintainers.

va_start(args, format);

[kunalspathak]

LGTM

[jakobbotsch]

/ba-g Failure is #116261