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author | Dietmar Maurer <dietmar@mono-cvs.ximian.com> | 2001-09-13 14:14:22 +0400 |
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committer | Dietmar Maurer <dietmar@mono-cvs.ximian.com> | 2001-09-13 14:14:22 +0400 |
commit | 649ad548c79bdb96abf96ec9df78e0655d576721 (patch) | |
tree | 95ecb9bee086fd18cda18b0c5bb177fe37ff6a53 /docs | |
parent | 123f4ab491e2c0bb8941c10c4dcff191aad932e5 (diff) |
added some thoughts
svn path=/trunk/mono/; revision=802
Diffstat (limited to 'docs')
-rw-r--r-- | docs/jit-thoughts | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/docs/jit-thoughts b/docs/jit-thoughts index 4d70b189bcd..14376478de8 100644 --- a/docs/jit-thoughts +++ b/docs/jit-thoughts @@ -1,5 +1,16 @@ Just some thoughts for the JITer: +General issues: +=============== + +We are designing a JIT compiler, so we have to consider two things: + +- the quality of the generated code +- the time needed to generate that code + +The current approach is to keep the JITer as simple as possible, and thus as +fast as possible. The generated code quality will suffer from that. + X86 register allocation: ======================== @@ -9,10 +20,37 @@ currently ignore that ability and always allocate 32 bit registers, because I think we would gain very little from that optimisation and it would complicate the code. +Different Register Sets: +======================== + +Most processors have more that one register set, at least one for floating +point values, and one for integers. Should we support architectures with more +that two sets? Does someone knows such an architecture? + +Register Allocation: +==================== + +With lcc you can assign a fixed register to a tree before register +allocation. For example this is needed by call, which return the value always +in EAX on x86. The current implementation works without such system (due to +special forest generation), and I wonder if we really need this feature? Forest generation: ================== +One idea was to drive the code generation directly from the CIL code, without +generating an intermediate forest of trees. I think this is not possible, +because you always have to gather some attributes and attach it to the +instruction (for example the register allocation info). So I thing generating a +tree is the right thing and that also works perfectly with monoburg. IMO we +would not get any benefit from trying to feed monoburg directly with CIL +instructions. + +We can also speedup the tree generation by using alloca instead of malloc. + +DAG handling: +============= + Monoburg can't handle DAGs, instead we need real trees as input for the code generator. So we have two problems: @@ -41,3 +79,11 @@ STLOC(ADD (LDLOC, LDLOC)) This is what lcc is doing, if I understood 12.8, page 342, 343? +Value Types: +============ + +The only CLI instructions which can handle value types are loads and stores, +either to local variable, to the stack or to array elements. Value types with a +size smaller than sizeof(int) are handled like any other basic type. For other +value types we load the base address and emit block copies to store them. + |