[Build] Add per-file up-to-date check in CompileNativeAssembly#11055
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[Build] Add per-file up-to-date check in CompileNativeAssembly#11055davidnguyen-tech wants to merge 2 commits intodotnet:mainfrom
davidnguyen-tech wants to merge 2 commits intodotnet:mainfrom
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When _CompileNativeAssemblySources runs, it recompiles ALL .ll files even if only some have changed. This is because MSBuild's target-level Inputs/Outputs is all-or-nothing — if any .ll file is newer than any .o file, every file gets recompiled. Add a per-file timestamp check in RunAssembler() — if the output .o is newer than the input .ll, that file is skipped. This saves time on incremental CoreCLR builds where upstream generators use CopyIfStreamChanged to preserve .ll timestamps for unchanged files. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Add CompileNativeAssemblySourcesSkipsUnchangedFiles integration test that verifies on incremental CoreCLR builds, unchanged .ll files are not recompiled by the CompileNativeAssembly task while changed .ll files are still correctly compiled. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Adds per-file timestamp comparison in the
CompileNativeAssemblytask to skip recompilation of.llfiles whose.ooutput is already up-to-date. This avoids unnecessaryllcinvocations on incremental CoreCLR builds.Problem
_CompileNativeAssemblySourcesrecompiles ALL.ll→.ofiles whenever ANY.llfile changes, because MSBuild's target-levelInputs/Outputsis all-or-nothing. On incremental CoreCLR builds, upstream generators already useFiles.CopyIfStreamChangedto preserve timestamps on unchanged.llfiles, but theCompileNativeAssemblytask has no per-file granularity — it recompiles everything when the target runs.Fix
Before running
llcfor each source file inRunAssembler(), check if the output.ofile exists and its timestamp is ≥ the input.llfile's timestamp. If so, skip that file and emit a debug log message.This preserves parallel compilation of changed files while skipping unchanged ones individually.
Expected Savings
On incremental CoreCLR builds where only typemaps change (due to assembly MVID changes), other
.llfiles (environment, marshal_methods, jni_remap) are skipped, saving roughly 50-70% of the ~2.85s_CompileNativeAssemblySourcescost.Testing
CompileNativeAssemblySourcesSkipsUnchangedFilesintegration test that verifies:_CompileNativeAssemblySourcestarget still runs (not skipped at target level).llfile is skipped at the per-file level (via log message assertion)