feat: add escape analysis MVP

[MeteorsLiu]

This draft starts the Phase 1 LLVM-IR escape-analysis MVP proposed in #2244.

The implementation includes:

• Add a sparse per-allocation LLVM use walker with conservative operand-role handling and exact forwarding through proven local alloca slots.
• Cache pointer-parameter summaries for heap, mutator, callee, result, and alignment facts, including direct-call composition and recursive fixed-point evaluation.
• Rewrite bounded local AllocZ and AllocU calls before large-aggregate and C ABI lowering, preserving zero initialization and rejecting loops, unsupported sizes, alignments, and address spaces.
• Drive focused pass coverage from literal LITTEST fixtures where in.txt contains input LLVM IR and out.txt contains the complete transformed module, plus a build-pipeline integration fixture.
• Keep call-argument alignment propagation and recursive alignment-level saturation as explicit follow-up correctness work before this draft is ready for review.

This establishes the LLGo-owned analysis and rewrite boundary while keeping unknown calls and unsupported LLVM behavior conservative.

[github-actions]

LLGo baseline benchmarks

5df423ea436b | workflow run | long-term charts

Program measurements

Platform	Workload	File size	vs main	Build	vs main	Run	vs main
Linux	cprintf	18544 B	new	351.155 ms	new	1.288 ms	new
Linux	fmtprintf	2214984 B	new	3.240 s	new	2.430 ms	new
Linux	println	71504 B	new	341.664 ms	new	1.584 ms	new
macOS	cprintf	84672 B	new	402.685 ms	new	3.275 ms	new
macOS	fmtprintf	2360880 B	new	3.326 s	new	23.826 ms	new
macOS	println	125712 B	new	403.087 ms	new	4.005 ms	new

Core language and compiler benchmarks

Platform	Benchmark	ns/op	vs main
Linux	BenchmarkLookupPCRandom	13.230 ns/op	new
Linux	BenchmarkMergeCompilerFlags	150 ns/op	new
Linux	BenchmarkMergeLinkerFlags	93.800 ns/op	new
Linux	BenchmarkChannelBuffered	35.510 ns/op	new
Linux	BenchmarkChannelHandoff	30201 ns/op	new
Linux	BenchmarkDefer	45.990 ns/op	new
Linux	BenchmarkDirectCall	1.557 ns/op	new
Linux	BenchmarkGlobalRead	1.872 ns/op	new
Linux	BenchmarkGlobalWrite	2.487 ns/op	new
Linux	BenchmarkGoroutine	45261 ns/op	new
Linux	BenchmarkInterfaceCall	8.094 ns/op	new
Linux	BenchmarkRuntimeGetG	2.490 ns/op	new
macOS	BenchmarkLookupPCRandom	15.330 ns/op	new
macOS	BenchmarkMergeCompilerFlags	139.300 ns/op	new
macOS	BenchmarkMergeLinkerFlags	91.390 ns/op	new
macOS	BenchmarkChannelBuffered	27.250 ns/op	new
macOS	BenchmarkChannelHandoff	7813 ns/op	new
macOS	BenchmarkDefer	45.280 ns/op	new
macOS	BenchmarkDirectCall	1.075 ns/op	new
macOS	BenchmarkGlobalRead	1.150 ns/op	new
macOS	BenchmarkGlobalWrite	1.049 ns/op	new
macOS	BenchmarkGoroutine	35879 ns/op	new
macOS	BenchmarkInterfaceCall	5.279 ns/op	new
macOS	BenchmarkRuntimeGetG	2.199 ns/op	new

No main baseline exists yet; all metrics are marked new.

Warning

• The rendered benchmark data could not be pushed.

[codecov]

Codecov Report

❌ Patch coverage is 48.88889% with 23 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/build/build.go	48.88%	15 Missing and 8 partials ⚠️

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