feat(variables): add -O2 fixture for broader location coverage - #1042
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feat(variables): add -O2 fixture for broader location coverage#1042JoshuaMoelans wants to merge 5 commits into
-O2 fixture for broader location coverage#1042JoshuaMoelans wants to merge 5 commits into
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variables_opt.c is a separate -O2 companion to variables.c, targeting the location shapes that cannot occur at -O0: register locations, sub-function ranges, and multi-range location lists (external_call's parameter moves rdi -> rbp across the rand() call). Liveness scaffolding uses noinline, a volatile input global, and an empty-asm USE(x) marker. Notable finds recorded in the snapshot/README: - same-TU calls don't split live ranges (GCC IPA-RA sees real clobbers); an external call is needed for multi-range lists - variables optimized to DW_AT_const_value are dropped by symbolic entirely (no empty entry), documented as a known gap Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Merge variables_opt.c into variables.c and compile the single source at both -O0 and -O2, per team decision: one source of truth, two fixture binaries, two snapshots. The liveness scaffolding (NOINLINE, opaque, USE) is a no-op at -O0, so the -O0 snapshot diff is purely additive: the location-oriented functions gain ordinary stack slots (including `gone`, whose -O0 presence now contrasts directly with its -O2 absence). The existing type-oriented functions get NOINLINE so -O2 cannot inline them into main; unscaffolded, they render (nearly) empty in the optimized snapshot, deliberately recording what optimization does to them. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Trim redundant framing and align the text with the merged single-source setup (two builds of variables.c, two snapshots). Expand the multi-range bullet to spell out why same-file calls do not split live ranges: GCC's interprocedural register allocation sees the callee's real clobbers, so multi-range coverage needs calls to external functions. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Add float_registers (USE_F, an SSE "x"-constraint variant of USE, since "r" only fits general-purpose registers) asserting DWARF registers 17+, and stack_home, whose volatile local keeps a frame-base location even at -O2. The volatile qualifier also reveals another type gap: it wraps the type in a DW_TAG_volatile_type that symbolic does not follow yet. Also correct the scaffolding docs based on a with/without-USE DWARF comparison: data flow alone keeps these values alive, but without the register pin GCC describes them as DW_OP_stack_value expressions, which symbolic drops from the snapshot. Entry-value/stack-value entries turn out to already exist in the fixture's DWARF (parameter tails in float_registers), so the README now records them as a present-but- dropped gap rather than coverage to be provoked later. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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-O2 fixture for broader location coverage
JoshuaMoelans
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-O2 fixture for broader location coverage-O2 fixture for broader location coverage
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This branch adds an optimized (
-O2) build of the variables fixture, to be merged in on top of #1038 .variables.cis now compiled twice from the same source —fixtures/linux/variables(-O0, unchanged coverage) andfixtures/linux/variables_opt— with the new binary asserted bytest_elf_variables_optand its own snapshot.The
-O2snapshot covers the location shapes that can't exist at-O0, where everything is a single whole-function stack slot:float_registersshows DWARF regs 17+)external_call's parameter moves rdi → rbp to survive therand()call)stack_homeKeeping variables alive at
-O2needs some scaffolding (NOINLINE, an opaquevolatileglobal, and empty-asmUSE/USE_Fmarkers), all of it a no-op at-O0. The non-obvious pitfalls we hit are written up in theREADME— e.g. calls within the same file don't split live ranges because GCC sees the callee's real register usage, so multi-range lists need an external call.The snapshots also record a few things symbolic doesn't extract yet, so future support shows up as a visible diff: variables reduced to
DW_AT_const_value(present at-O0, silently absent at-O2),DW_OP_entry_value/DW_OP_stack_valuelocation entries (already in the fixture's DWARF, currently dropped — it's why parameters end early in the optimized snapshot), and volatile-qualified types rendering asUnknown.