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Diffstat (limited to 'includes/TailCalls.h')
| -rw-r--r-- | includes/TailCalls.h | 272 |
1 files changed, 272 insertions, 0 deletions
diff --git a/includes/TailCalls.h b/includes/TailCalls.h new file mode 100644 index 0000000000..670da9546f --- /dev/null +++ b/includes/TailCalls.h @@ -0,0 +1,272 @@ +/* ----------------------------------------------------------------------------- + * + * (c) The GHC Team, 1998-1999 + * + * Stuff for implementing proper tail jumps. + * + * ---------------------------------------------------------------------------*/ + +#ifndef TAILCALLS_H +#define TAILCALLS_H + +/* ----------------------------------------------------------------------------- + Unmangled tail-jumping: use the mini interpretter. + -------------------------------------------------------------------------- */ + +#ifdef USE_MINIINTERPRETER + +#define JMP_(cont) return((StgFunPtr)(cont)) +#define FB_ +#define FE_ + +#else + +extern void __DISCARD__(void); + +/* ----------------------------------------------------------------------------- + Tail calling on x86 + -------------------------------------------------------------------------- */ + +#if i386_HOST_ARCH + +/* Note about discard: possibly there to fool GCC into clearing up + before we do the jump eg. if there are some arguments left on the C + stack that GCC hasn't popped yet. Also possibly to fool any + optimisations (a function call often acts as a barrier). Not sure + if any of this is necessary now -- SDM + + Comment to above note: I don't think the __DISCARD__() in JMP_ is + necessary. Arguments should be popped from the C stack immediately + after returning from a function, as long as we pass -fno-defer-pop + to gcc. Moreover, a goto to a first-class label acts as a barrier + for optimisations in the same way a function call does. + -= chak + */ + +/* The goto here seems to cause gcc -O2 to delete all the code after + it - including the FE_ marker and the epilogue code - exactly what + we want! -- SDM + */ + +#define JMP_(cont) \ + { \ + void *__target; \ + __DISCARD__(); \ + __target = (void *)(cont); \ + goto *__target; \ + } + +#endif /* i386_HOST_ARCH */ + +/* ----------------------------------------------------------------------------- + Tail calling on x86_64 + -------------------------------------------------------------------------- */ + +#if x86_64_HOST_ARCH + +/* + NOTE about __DISCARD__(): + + On x86_64 this is necessary to work around bugs in the register + variable support in gcc. Without the __DISCARD__() call, gcc will + silently throw away assignements to global register variables that + happen before the jump. + + Here's the example: + + extern void g(void); + static void f(void) { + R1 = g; + __DISCARD__() + goto *R1; + } + + without the dummy function call, gcc throws away the assignment to R1 + (gcc 3.4.3) gcc bug #20359. +*/ + +#define JMP_(cont) \ + { \ + __DISCARD__(); \ + goto *(void *)(cont); \ + } + +#endif /* x86_64_HOST_ARCH */ + +/* ----------------------------------------------------------------------------- + Tail calling on Sparc + -------------------------------------------------------------------------- */ + +#ifdef sparc_HOST_ARCH + +#define JMP_(cont) ((F_) (cont))() + /* Oh so happily, the above turns into a "call" instruction, + which, on a SPARC, is nothing but a "jmpl" with the + return address in %o7 [which we don't care about]. + */ + +/* Don't need these for sparc mangling */ +#define FB_ +#define FE_ + +#endif /* sparc_HOST_ARCH */ + +/* ----------------------------------------------------------------------------- + Tail calling on Alpha + -------------------------------------------------------------------------- */ + +#ifdef alpha_HOST_ARCH + +#if IN_STG_CODE +register void *_procedure __asm__("$27"); +#endif + +#define JMP_(cont) \ + do { _procedure = (void *)(cont); \ + __DISCARD__(); \ + goto *_procedure; \ + } while(0) + +/* Don't need these for alpha mangling */ +#define FB_ +#define FE_ + +#endif /* alpha_HOST_ARCH */ + +/* ----------------------------------------------------------------------------- + Tail calling on HP + +Description of HP's weird procedure linkage, many thanks to Andy Bennet +<andy_bennett@hp.com>: + +I've been digging a little further into the problem of how HP-UX does +dynamic procedure calls. My solution in the last e-mail inserting an extra +'if' statement into the JMP_ I think is probably the best general solution I +can come up with. There are still a few problems with it however: It wont +work, if JMP_ ever has to call anything in a shared library, if this is +likely to be required it'll need something more elaborate. It also wont work +with PA-RISC 2.0 wide mode (64-bit) which uses a different format PLT. + +I had some feedback from someone in HP's compiler lab and the problem +relates to the linker on HP-UX, not gcc as I first suspected. The reason the +'hsc' executable works is most likely due to a change in 'ld's behaviour for +performance reasons between your revision and mine. + +The major issue relating to this is shared libraries and how they are +implented under HP-UX. The whole point of the Procedure Label Table (PLT) is +to allow a function pointer to hold the address of the function and a +pointer to the library's global data lookup table (DLT) used by position +independent code (PIC). This makes the PLT absolutely essential for shared +library calls. HP has two linker introduced assembly functions for dealing +with dynamic calls, $$dyncall and $$dyncall_external. The former does a +check to see if the address is a PLT pointer and dereferences if necessary +or just calls the address otherwise; the latter skips the check and just +does the indirect jump no matter what. + +Since $$dyncall_external runs faster due to its not having the test, the +linker nowadays prefers to generate calls to that, rather than $$dyncall. It +makes this decision based on the presence of any shared library. If it even +smells an sl's existence at link time, it rigs the runtime system to +generate PLT references for everything on the assumption that the result +will be slightly more efficient. This is what is crashing GHC since the +calls it is generating have no understanding of the procedure label proper. +The only way to get real addresses is to link everything archive, including +system libraries, at which point it assumes you probably are going to be +using calls similar to GHC's (its rigged for HP's +ESfic compiler option) +but uses $$dyncall if necessary to cope, just in case you aren't. + + -------------------------------------------------------------------------- */ + +#ifdef hppa1_1_hp_hpux_TARGET + +#define JMP_(cont) \ + do { void *_procedure = (void *)(cont); \ + if (((int) _procedure) & 2) \ + _procedure = (void *)(*((int *) (_procedure - 2))); \ + goto *_procedure; \ + } while(0) + +#endif /* hppa1_1_hp_hpux_TARGET */ + +/* ----------------------------------------------------------------------------- + Tail calling on PowerPC + -------------------------------------------------------------------------- */ + +#ifdef powerpc_HOST_ARCH + +#define JMP_(cont) \ + { \ + void *target; \ + target = (void *)(cont); \ + __DISCARD__(); \ + goto *target; \ + } + +/* + The __DISCARD__ is there because Apple's April 2002 Beta of GCC 3.1 + sometimes generates incorrect code otherwise. + It tends to "forget" to update global register variables in the presence + of decrement/increment operators: + JMP_(*(--Sp)) is wrongly compiled as JMP_(Sp[-1]). + Calling __DISCARD__ in between works around this problem. +*/ + +/* + I would _love_ to use the following instead, + but some versions of Apple's GCC fail to generate code for it + if it is called for a casted data pointer - which is exactly what + we are going to do... + + #define JMP_(cont) ((F_) (cont))() +*/ + +#endif /* powerpc_HOST_ARCH */ + +#ifdef powerpc64_HOST_ARCH +#define JMP_(cont) ((F_) (cont))() +#endif + +/* ----------------------------------------------------------------------------- + Tail calling on IA64 + -------------------------------------------------------------------------- */ + +#ifdef ia64_HOST_ARCH + +/* The compiler can more intelligently decide how to do this. We therefore + * implement it as a call and optimise to a jump at mangle time. */ +#define JMP_(cont) ((F_) (cont))(); __asm__ volatile ("--- TAILCALL ---"); + +/* Don't emit calls to __DISCARD__ as this causes hassles */ +#define __DISCARD__() + +#endif + +/* ----------------------------------------------------------------------------- + FUNBEGIN and FUNEND. + + These are markers indicating the start and end of Real Code in a + function. All instructions between the actual start and end of the + function and these markers is shredded by the mangler. + -------------------------------------------------------------------------- */ + +/* The following __DISCARD__() has become necessary with gcc 2.96 on x86. + * It prevents gcc from moving stack manipulation code from the function + * body (aka the Real Code) into the function prologue, ie, from moving it + * over the --- BEGIN --- marker. It should be noted that (like some + * other black magic in GHC's code), there is no essential reason why gcc + * could not move some stack manipulation code across the __DISCARD__() - + * it just doesn't choose to do it at the moment. + * -= chak + */ + +#ifndef FB_ +#define FB_ __asm__ volatile ("--- BEGIN ---"); __DISCARD__ (); +#endif + +#ifndef FE_ +#define FE_ __asm__ volatile ("--- END ---"); +#endif + +#endif /* !USE_MINIINTERPRETER */ + +#endif /* TAILCALLS_H */ |