| Commit message (Collapse) | Author | Age | Files | Lines |
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Previously, the elimination of useless conditions done in the 2nd pass of the tunneling
introduced some new "nop" instructions that were not eliminated.
This commit solves this issue by anticipating the elimination of conditions in the 1st pass
of the tunneling, the 2nd pass being unchanged.
In case of cycles in the CFG, the full elimination of useless conditions may require several
iterations in the 1st pass. Moreover, in the simulation proof, the measure counting the number of
eliminated steps from each node, needs to be adapted according to the modifications on the 1st pass.
Hence, this measure results from a quite complex fixpoint computation: proving its properties
would be very difficult.
This leads us to introduce an oracle, implementing the first pass and producing the expected
measure. A certified verifier directly checks that the measure provided by the oracle
satisfies the properties expected by the simulation proof.
Introducing this oracle/verifier pair has here the following advantage:
- the proof is simpler than the original one (e.g. having a certified union-find structure
is no more necessary for this pass).
- the oracle is very efficient, by using imperative data-structure to compute memoized
fixpoints.
At runtime, the overhead induced by the verifier computations (and the actual computation of
the measure) seems largely compensated by the gains obtained through the imperative oracle.
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This commit eliminates useless conditional branches during the branch tunneling pass over LTL. Conditional branches where both successors go to the same LTL node are turned into unconditional branches, which will stay or be eliminated by the subsequent Linear pass.
One code pattern that triggers this optimization is an empty if/else at the C source level. Commit 4d7a459 eliminates these empty if/else statements early, during the Compcert C -> Clight translation. I think it's good to have both optimizations:
- Early elimination makes sure these empty if/else cause no overhead whatsoever, and in particular cannot degrade the precision of later static analyses.
- Late elimination catches the case where a nonempty if/else in the source becomes empty as a consequence of optimizations.
Future work? If the optimization in Tunneling triggers, it might be worth re-running the Tunneling pass once more, to make sure that the "Lgoto" introduced by the optimization is properly tunneled / skipped over when appropriate.
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1- new register allocator (+ live range splitting, spilling&reloading, etc)
based on a posteriori validation using the Rideau-Leroy algorithm
2- support for 64-bit integer arithmetic (type "long long").
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2200 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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Update ARM port.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2085 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1989 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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AST: add ef_inline flag to external functions.
Selection: recognize calls to inlined built-ins and inline them as Sbuiltin.
CminorSel to Asm: added Sbuiltin/Ibuiltin instruction.
PrintAsm: adapted expansion of builtins.
C2Clight: adapted detection of builtins.
Conventions: refactored in a machine-independent part (backend/Conventions)
and a machine-dependent part (ARCH/SYS/Conventions1).
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1356 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1171 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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Kildall: simplified the interface
Constprop, CSE, Allocation, Linearize: updated for the new Kildall
RTL, LTL: removed the well-formedness condition on the CFG,
it is no longer necessary with the new Kildall and it is problematic
for validated optimizations.
Maps: more efficient implementation of PTree.fold.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1124 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1120 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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- In Cminor and below, removed pointer validity check in semantics of
comparisons, so that evaluation of expressions is independent of
memory state.
- In Cminor and below, removed "alloc" instruction.
- Cleaned up commented-away parts.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@945 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@489 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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En particulier:
- Semantiques small-step depuis RTL jusqu'a PPC
- Cminor independant du processeur
- Ajout passes Selection et Reload
- Ajout des langages intermediaires CminorSel et LTLin correspondants
- Ajout des tailcalls depuis Cminor jusqu'a PPC
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@384 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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- Ajout de traces d'evenements d'E/S dans les semantiques
- Ajout constructions switch et allocation dynamique
- Initialisation des variables globales
- Portage Coq 8.1 beta
Debut d'integration du front-end C:
- Traduction Clight -> Csharpminor dans cfrontend/
- Modifications de Csharpminor et Globalenvs en consequence.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@72 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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