CgUtils.hs 23.1 KB
Newer Older
1 2 3 4
-----------------------------------------------------------------------------
--
-- Code generator utilities; mostly monadic
--
Simon Marlow's avatar
Simon Marlow committed
5
-- (c) The University of Glasgow 2004-2006
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
--
-----------------------------------------------------------------------------

module CgUtils (
	addIdReps,
	cgLit,
	emitDataLits, emitRODataLits, emitIf, emitIfThenElse,
	emitRtsCall, emitRtsCallWithVols, emitRtsCallWithResult,
	assignTemp, newTemp,
	emitSimultaneously,
	emitSwitch, emitLitSwitch,
	tagToClosure,

	cmmAndWord, cmmOrWord, cmmNegate, cmmEqWord, cmmNeWord,
	cmmOffsetExprW, cmmOffsetExprB,
	cmmRegOffW, cmmRegOffB,
	cmmLabelOffW, cmmLabelOffB,
	cmmOffsetW, cmmOffsetB,
	cmmOffsetLitW, cmmOffsetLitB,
	cmmLoadIndexW,

	addToMem, addToMemE,
	mkWordCLit,
29
	mkStringCLit, mkByteStringCLit,
30 31 32 33 34 35 36
	packHalfWordsCLit,
	blankWord
  ) where

#include "HsVersions.h"

import CgMonad
Simon Marlow's avatar
Simon Marlow committed
37 38 39 40
import TyCon
import Id
import Constants
import SMRep
41 42 43 44
import PprCmm		( {- instances -} )
import Cmm
import CLabel
import CmmUtils
Simon Marlow's avatar
Simon Marlow committed
45 46 47 48 49 50 51 52 53
import MachOp
import ForeignCall
import Literal
import Digraph
import ListSetOps
import Util
import DynFlags
import FastString
import PackageConfig
54 55
import Outputable

56 57 58 59 60 61
import MachRegs (callerSaveVolatileRegs)
  -- HACK: this is part of the NCG so we shouldn't use this, but we need
  -- it for now to eliminate the need for saved regs to be in CmmCall.
  -- The long term solution is to factor callerSaveVolatileRegs
  -- from nativeGen into codeGen

Simon Marlow's avatar
Simon Marlow committed
62 63 64 65
import Data.Char
import Data.Bits
import Data.Word
import Data.Maybe
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82

-------------------------------------------------------------------------
--
--	Random small functions
--
-------------------------------------------------------------------------

addIdReps :: [Id] -> [(CgRep, Id)]
addIdReps ids = [(idCgRep id, id) | id <- ids]

-------------------------------------------------------------------------
--
--	Literals
--
-------------------------------------------------------------------------

cgLit :: Literal -> FCode CmmLit
83 84
cgLit (MachStr s) = mkByteStringCLit (bytesFS s)
 -- not unpackFS; we want the UTF-8 byte stream.
85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159
cgLit other_lit   = return (mkSimpleLit other_lit)

mkSimpleLit :: Literal -> CmmLit
mkSimpleLit (MachChar	c)    = CmmInt (fromIntegral (ord c)) wordRep
mkSimpleLit MachNullAddr      = zeroCLit
mkSimpleLit (MachInt i)       = CmmInt i wordRep
mkSimpleLit (MachInt64 i)     = CmmInt i I64
mkSimpleLit (MachWord i)      = CmmInt i wordRep
mkSimpleLit (MachWord64 i)    = CmmInt i I64
mkSimpleLit (MachFloat r)     = CmmFloat r F32
mkSimpleLit (MachDouble r)    = CmmFloat r F64
mkSimpleLit (MachLabel fs ms) = CmmLabel (mkForeignLabel fs ms is_dyn)
			      where
				is_dyn = False	-- ToDo: fix me
	
mkLtOp :: Literal -> MachOp
-- On signed literals we must do a signed comparison
mkLtOp (MachInt _)    = MO_S_Lt wordRep
mkLtOp (MachFloat _)  = MO_S_Lt F32
mkLtOp (MachDouble _) = MO_S_Lt F64
mkLtOp lit	      = MO_U_Lt (cmmLitRep (mkSimpleLit lit))


---------------------------------------------------
--
--	Cmm data type functions
--
---------------------------------------------------

-----------------------
-- The "B" variants take byte offsets
cmmRegOffB :: CmmReg -> ByteOff -> CmmExpr
cmmRegOffB = cmmRegOff

cmmOffsetB :: CmmExpr -> ByteOff -> CmmExpr
cmmOffsetB = cmmOffset

cmmOffsetExprB :: CmmExpr -> CmmExpr -> CmmExpr
cmmOffsetExprB = cmmOffsetExpr

cmmLabelOffB :: CLabel -> ByteOff -> CmmLit
cmmLabelOffB = cmmLabelOff

cmmOffsetLitB :: CmmLit -> ByteOff -> CmmLit
cmmOffsetLitB = cmmOffsetLit

-----------------------
-- The "W" variants take word offsets
cmmOffsetExprW :: CmmExpr -> CmmExpr -> CmmExpr
-- The second arg is a *word* offset; need to change it to bytes
cmmOffsetExprW e (CmmLit (CmmInt n _)) = cmmOffsetW e (fromInteger n)
cmmOffsetExprW e wd_off = cmmIndexExpr wordRep e wd_off

cmmOffsetW :: CmmExpr -> WordOff -> CmmExpr
cmmOffsetW e n = cmmOffsetB e (wORD_SIZE * n)

cmmRegOffW :: CmmReg -> WordOff -> CmmExpr
cmmRegOffW reg wd_off = cmmRegOffB reg (wd_off * wORD_SIZE)

cmmOffsetLitW :: CmmLit -> WordOff -> CmmLit
cmmOffsetLitW lit wd_off = cmmOffsetLitB lit (wORD_SIZE * wd_off)

cmmLabelOffW :: CLabel -> WordOff -> CmmLit
cmmLabelOffW lbl wd_off = cmmLabelOffB lbl (wORD_SIZE * wd_off)

cmmLoadIndexW :: CmmExpr -> Int -> CmmExpr
cmmLoadIndexW base off
  = CmmLoad (cmmOffsetW base off) wordRep

-----------------------
cmmNeWord, cmmEqWord, cmmOrWord, cmmAndWord :: CmmExpr -> CmmExpr -> CmmExpr
cmmOrWord  e1 e2 = CmmMachOp mo_wordOr  [e1, e2]
cmmAndWord e1 e2 = CmmMachOp mo_wordAnd [e1, e2]
cmmNeWord  e1 e2 = CmmMachOp mo_wordNe  [e1, e2]
cmmEqWord  e1 e2 = CmmMachOp mo_wordEq  [e1, e2]
160
cmmULtWord e1 e2 = CmmMachOp mo_wordULt [e1, e2]
161
cmmUGeWord e1 e2 = CmmMachOp mo_wordUGe [e1, e2]
162
cmmUGtWord e1 e2 = CmmMachOp mo_wordUGt [e1, e2]
163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217

cmmNegate :: CmmExpr -> CmmExpr
cmmNegate (CmmLit (CmmInt n rep)) = CmmLit (CmmInt (-n) rep)
cmmNegate e			  = CmmMachOp (MO_S_Neg (cmmExprRep e)) [e]

blankWord :: CmmStatic
blankWord = CmmUninitialised wORD_SIZE

-----------------------
--	Making literals

mkWordCLit :: StgWord -> CmmLit
mkWordCLit wd = CmmInt (fromIntegral wd) wordRep

packHalfWordsCLit :: (Integral a, Integral b) => a -> b -> CmmLit
-- Make a single word literal in which the lower_half_word is
-- at the lower address, and the upper_half_word is at the 
-- higher address
-- ToDo: consider using half-word lits instead
-- 	 but be careful: that's vulnerable when reversed
packHalfWordsCLit lower_half_word upper_half_word
#ifdef WORDS_BIGENDIAN
   = mkWordCLit ((fromIntegral lower_half_word `shiftL` hALF_WORD_SIZE_IN_BITS)
		 .|. fromIntegral upper_half_word)
#else 
   = mkWordCLit ((fromIntegral lower_half_word) 
		 .|. (fromIntegral upper_half_word `shiftL` hALF_WORD_SIZE_IN_BITS))
#endif

--------------------------------------------------------------------------
--
-- Incrementing a memory location
--
--------------------------------------------------------------------------

addToMem :: MachRep 	-- rep of the counter
	 -> CmmExpr	-- Address
	 -> Int		-- What to add (a word)
	 -> CmmStmt
addToMem rep ptr n = addToMemE rep ptr (CmmLit (CmmInt (toInteger n) rep))

addToMemE :: MachRep 	-- rep of the counter
	  -> CmmExpr	-- Address
	  -> CmmExpr	-- What to add (a word-typed expression)
	  -> CmmStmt
addToMemE rep ptr n
  = CmmStore ptr (CmmMachOp (MO_Add rep) [CmmLoad ptr rep, n])

-------------------------------------------------------------------------
--
--	Converting a closure tag to a closure for enumeration types
--      (this is the implementation of tagToEnum#).
--
-------------------------------------------------------------------------

Simon Marlow's avatar
Simon Marlow committed
218 219
tagToClosure :: PackageId -> TyCon -> CmmExpr -> CmmExpr
tagToClosure this_pkg tycon tag
220
  = CmmLoad (cmmOffsetExprW closure_tbl tag) wordRep
221
  where closure_tbl = CmmLit (CmmLabel lbl)
Simon Marlow's avatar
Simon Marlow committed
222
	lbl = mkClosureTableLabel this_pkg (tyConName tycon)
223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284

-------------------------------------------------------------------------
--
--	Conditionals and rts calls
--
-------------------------------------------------------------------------

emitIf :: CmmExpr 	-- Boolean
       -> Code		-- Then part
       -> Code		
-- Emit (if e then x)
-- ToDo: reverse the condition to avoid the extra branch instruction if possible
-- (some conditionals aren't reversible. eg. floating point comparisons cannot
-- be inverted because there exist some values for which both comparisons
-- return False, such as NaN.)
emitIf cond then_part
  = do { then_id <- newLabelC
       ; join_id <- newLabelC
       ; stmtC (CmmCondBranch cond then_id)
       ; stmtC (CmmBranch join_id)
       ; labelC then_id
       ; then_part
       ; labelC join_id
       }

emitIfThenElse :: CmmExpr 	-- Boolean
       		-> Code		-- Then part
       		-> Code		-- Else part
       		-> Code		
-- Emit (if e then x else y)
emitIfThenElse cond then_part else_part
  = do { then_id <- newLabelC
       ; else_id <- newLabelC
       ; join_id <- newLabelC
       ; stmtC (CmmCondBranch cond then_id)
       ; else_part
       ; stmtC (CmmBranch join_id)
       ; labelC then_id
       ; then_part
       ; labelC join_id
       }

emitRtsCall :: LitString -> [(CmmExpr,MachHint)] -> Code
emitRtsCall fun args = emitRtsCall' [] fun args Nothing
   -- The 'Nothing' says "save all global registers"

emitRtsCallWithVols :: LitString -> [(CmmExpr,MachHint)] -> [GlobalReg] -> Code
emitRtsCallWithVols fun args vols
   = emitRtsCall' [] fun args (Just vols)

emitRtsCallWithResult :: CmmReg -> MachHint -> LitString
	-> [(CmmExpr,MachHint)] -> Code
emitRtsCallWithResult res hint fun args
   = emitRtsCall' [(res,hint)] fun args Nothing

-- Make a call to an RTS C procedure
emitRtsCall'
   :: [(CmmReg,MachHint)]
   -> LitString
   -> [(CmmExpr,MachHint)]
   -> Maybe [GlobalReg]
   -> Code
285 286 287 288
emitRtsCall' res fun args vols = do
    stmtsC caller_save
    stmtC (CmmCall target res args)
    stmtsC caller_load
289
  where
290
    (caller_save, caller_load) = callerSaveVolatileRegs vols
291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308
    target   = CmmForeignCall fun_expr CCallConv
    fun_expr = mkLblExpr (mkRtsCodeLabel fun)


-------------------------------------------------------------------------
--
--	Strings gnerate a top-level data block
--
-------------------------------------------------------------------------

emitDataLits :: CLabel -> [CmmLit] -> Code
-- Emit a data-segment data block
emitDataLits lbl lits
  = emitData Data (CmmDataLabel lbl : map CmmStaticLit lits)

emitRODataLits :: CLabel -> [CmmLit] -> Code
-- Emit a read-only data block
emitRODataLits lbl lits
309 310 311 312 313 314
  = emitData section (CmmDataLabel lbl : map CmmStaticLit lits)
  where section | any needsRelocation lits = RelocatableReadOnlyData
                | otherwise                = ReadOnlyData
        needsRelocation (CmmLabel _)      = True
        needsRelocation (CmmLabelOff _ _) = True
        needsRelocation _                 = False
315 316 317 318

mkStringCLit :: String -> FCode CmmLit
-- Make a global definition for the string,
-- and return its label
319 320 321 322
mkStringCLit str = mkByteStringCLit (map (fromIntegral.ord) str)

mkByteStringCLit :: [Word8] -> FCode CmmLit
mkByteStringCLit bytes
323
  = do 	{ uniq <- newUnique
324
	; let lbl = mkStringLitLabel uniq
325
	; emitData ReadOnlyData [CmmDataLabel lbl, CmmString bytes]
326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373
	; return (CmmLabel lbl) }

-------------------------------------------------------------------------
--
--	Assigning expressions to temporaries
--
-------------------------------------------------------------------------

assignTemp :: CmmExpr -> FCode CmmExpr
-- For a non-trivial expression, e, create a local
-- variable and assign the expression to it
assignTemp e 
  | isTrivialCmmExpr e = return e
  | otherwise 	       = do { reg <- newTemp (cmmExprRep e)
			    ; stmtC (CmmAssign reg e)
			    ; return (CmmReg reg) }


newTemp :: MachRep -> FCode CmmReg
newTemp rep = do { uniq <- newUnique; return (CmmLocal (LocalReg uniq rep)) }


-------------------------------------------------------------------------
--
--	Building case analysis
--
-------------------------------------------------------------------------

emitSwitch
	:: CmmExpr  		  -- Tag to switch on
	-> [(ConTagZ, CgStmts)]	  -- Tagged branches
	-> Maybe CgStmts	  -- Default branch (if any)
	-> ConTagZ -> ConTagZ	  -- Min and Max possible values; behaviour
				  -- 	outside this range is undefined
	-> Code

-- ONLY A DEFAULT BRANCH: no case analysis to do
emitSwitch tag_expr [] (Just stmts) _ _
  = emitCgStmts stmts

-- Right, off we go
emitSwitch tag_expr branches mb_deflt lo_tag hi_tag
  = 	-- Just sort the branches before calling mk_sritch
    do	{ mb_deflt_id <-
		case mb_deflt of
		  Nothing    -> return Nothing
		  Just stmts -> do id <- forkCgStmts stmts; return (Just id)

374 375 376 377
	; dflags <- getDynFlags
	; let via_C | HscC <- hscTarget dflags = True
		    | otherwise                = False

378
	; stmts <- mk_switch tag_expr (sortLe le branches) 
379
			mb_deflt_id lo_tag hi_tag via_C
380 381 382
	; emitCgStmts stmts
	}
  where
383
    (t1,_) `le` (t2,_) = t1 <= t2
384 385 386


mk_switch :: CmmExpr -> [(ConTagZ, CgStmts)]
387
	  -> Maybe BlockId -> ConTagZ -> ConTagZ -> Bool
388 389 390
	  -> FCode CgStmts

-- SINGLETON TAG RANGE: no case analysis to do
391
mk_switch tag_expr [(tag,stmts)] _ lo_tag hi_tag via_C
392 393 394 395 396
  | lo_tag == hi_tag
  = ASSERT( tag == lo_tag )
    return stmts

-- SINGLETON BRANCH, NO DEFUALT: no case analysis to do
397
mk_switch tag_expr [(tag,stmts)] Nothing lo_tag hi_tag via_C
398 399 400 401 402 403 404 405
  = return stmts
	-- The simplifier might have eliminated a case
	-- 	 so we may have e.g. case xs of 
	--				 [] -> e
	-- In that situation we can be sure the (:) case 
	-- can't happen, so no need to test

-- SINGLETON BRANCH: one equality check to do
406
mk_switch tag_expr [(tag,stmts)] (Just deflt) lo_tag hi_tag via_C
407 408 409 410 411 412 413 414 415 416
  = return (CmmCondBranch cond deflt `consCgStmt` stmts)
  where
    cond  =  cmmNeWord tag_expr (CmmLit (mkIntCLit tag))
	-- We have lo_tag < hi_tag, but there's only one branch, 
	-- so there must be a default

-- ToDo: we might want to check for the two branch case, where one of
-- the branches is the tag 0, because comparing '== 0' is likely to be
-- more efficient than other kinds of comparison.

417 418 419 420 421 422 423 424 425 426
-- DENSE TAG RANGE: use a switch statment.
--
-- We also use a switch uncoditionally when compiling via C, because
-- this will get emitted as a C switch statement and the C compiler
-- should do a good job of optimising it.  Also, older GCC versions
-- (2.95 in particular) have problems compiling the complicated
-- if-trees generated by this code, so compiling to a switch every
-- time works around that problem.
--
mk_switch tag_expr branches mb_deflt lo_tag hi_tag via_C
427
  | use_switch 	-- Use a switch
428
  = do	{ branch_ids <- mapM forkCgStmts (map snd branches)
429
	; let 
430
		tagged_blk_ids = zip (map fst branches) (map Just branch_ids)
431

432 433
		find_branch :: ConTagZ -> Maybe BlockId
		find_branch i = assocDefault mb_deflt tagged_blk_ids i
434

435 436 437 438
		-- NB. we have eliminated impossible branches at
		-- either end of the range (see below), so the first
		-- tag of a real branch is real_lo_tag (not lo_tag).
		arms = [ find_branch i | i <- [real_lo_tag..real_hi_tag]]
439

440
	        switch_stmt = CmmSwitch (cmmOffset tag_expr (- real_lo_tag)) arms
441

442 443
	; ASSERT(not (all isNothing arms)) 
	  return (oneCgStmt switch_stmt)
444 445
	}

446 447 448 449
  -- if we can knock off a bunch of default cases with one if, then do so
  | Just deflt <- mb_deflt, (lowest_branch - lo_tag) >= n_branches
  = do { (assign_tag, tag_expr') <- assignTemp' tag_expr
       ; let cond = cmmULtWord tag_expr' (CmmLit (mkIntCLit lowest_branch))
450
	     branch = CmmCondBranch cond deflt
451 452
       ; stmts <- mk_switch tag_expr' branches mb_deflt 
			lowest_branch hi_tag via_C
453
       ; return (assign_tag `consCgStmt` (branch `consCgStmt` stmts))
454 455 456 457 458
       }

  | Just deflt <- mb_deflt, (hi_tag - highest_branch) >= n_branches
  = do { (assign_tag, tag_expr') <- assignTemp' tag_expr
       ; let cond = cmmUGtWord tag_expr' (CmmLit (mkIntCLit highest_branch))
459
	     branch = CmmCondBranch cond deflt
460 461
       ; stmts <- mk_switch tag_expr' branches mb_deflt 
			lo_tag highest_branch via_C
462
       ; return (assign_tag `consCgStmt` (branch `consCgStmt` stmts))
463 464
       }

465 466 467
  | otherwise	-- Use an if-tree
  = do	{ (assign_tag, tag_expr') <- assignTemp' tag_expr
		-- To avoid duplication
468 469 470 471
	; lo_stmts <- mk_switch tag_expr' lo_branches mb_deflt 
				lo_tag (mid_tag-1) via_C
	; hi_stmts <- mk_switch tag_expr' hi_branches mb_deflt 
				mid_tag hi_tag via_C
472 473 474 475
	; hi_id <- forkCgStmts hi_stmts
	; let cond = cmmUGeWord tag_expr' (CmmLit (mkIntCLit mid_tag))
	      branch_stmt = CmmCondBranch cond hi_id
	; return (assign_tag `consCgStmt` (branch_stmt `consCgStmt` lo_stmts)) 
476
	}
477 478 479 480 481 482 483
	-- we test (e >= mid_tag) rather than (e < mid_tag), because
	-- the former works better when e is a comparison, and there
	-- are two tags 0 & 1 (mid_tag == 1).  In this case, the code
	-- generator can reduce the condition to e itself without
	-- having to reverse the sense of the comparison: comparisons
	-- can't always be easily reversed (eg. floating
	-- pt. comparisons).
484
  where
485 486
    use_switch 	 = {- pprTrace "mk_switch" (
			ppr tag_expr <+> text "n_tags:" <+> int n_tags <+>
487
                        text "branches:" <+> ppr (map fst branches) <+>
488
			text "n_branches:" <+> int n_branches <+>
489 490 491 492
			text "lo_tag:" <+> int lo_tag <+>
			text "hi_tag:" <+> int hi_tag <+>
			text "real_lo_tag:" <+> int real_lo_tag <+>
			text "real_hi_tag:" <+> int real_hi_tag) $ -}
493
		   ASSERT( n_branches > 1 && n_tags > 1 ) 
494 495 496 497 498
		   n_tags > 2 && (via_C || (dense && big_enough))
		 -- up to 4 branches we use a decision tree, otherwise
                 -- a switch (== jump table in the NCG).  This seems to be
                 -- optimal, and corresponds with what gcc does.
    big_enough 	 = n_branches > 4
499 500 501
    dense      	 = n_branches > (n_tags `div` 2)
    n_branches   = length branches
    
502 503 504 505 506 507 508 509 510 511 512 513 514 515 516
    -- ignore default slots at each end of the range if there's 
    -- no default branch defined.
    lowest_branch  = fst (head branches)
    highest_branch = fst (last branches)

    real_lo_tag
	| isNothing mb_deflt = lowest_branch
	| otherwise          = lo_tag

    real_hi_tag
	| isNothing mb_deflt = highest_branch
	| otherwise          = hi_tag

    n_tags = real_hi_tag - real_lo_tag + 1

517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543
	-- INVARIANT: Provided hi_tag > lo_tag (which is true)
	--	lo_tag <= mid_tag < hi_tag
	--	lo_branches have tags <  mid_tag
	--	hi_branches have tags >= mid_tag

    (mid_tag,_) = branches !! (n_branches `div` 2)
	-- 2 branches => n_branches `div` 2 = 1
	--	      => branches !! 1 give the *second* tag
	-- There are always at least 2 branches here

    (lo_branches, hi_branches) = span is_lo branches
    is_lo (t,_) = t < mid_tag


assignTemp' e
  | isTrivialCmmExpr e = return (CmmNop, e)
  | otherwise          = do { reg <- newTemp (cmmExprRep e)
                            ; return (CmmAssign reg e, CmmReg reg) }


emitLitSwitch :: CmmExpr			-- Tag to switch on
	      -> [(Literal, CgStmts)]		-- Tagged branches
	      -> CgStmts			-- Default branch (always)
	      -> Code				-- Emit the code
-- Used for general literals, whose size might not be a word, 
-- where there is always a default case, and where we don't know
-- the range of values for certain.  For simplicity we always generate a tree.
544 545 546
--
-- ToDo: for integers we could do better here, perhaps by generalising
-- mk_switch and using that.  --SDM 15/09/2004
547 548 549 550 551
emitLitSwitch scrut [] deflt 
  = emitCgStmts deflt
emitLitSwitch scrut branches deflt_blk
  = do	{ scrut' <- assignTemp scrut
	; deflt_blk_id <- forkCgStmts deflt_blk
552
	; blk <- mk_lit_switch scrut' deflt_blk_id (sortLe le branches)
553 554
	; emitCgStmts blk }
  where
555
    le (t1,_) (t2,_) = t1 <= t2
556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696

mk_lit_switch :: CmmExpr -> BlockId 
 	      -> [(Literal,CgStmts)]
	      -> FCode CgStmts
mk_lit_switch scrut deflt_blk_id [(lit,blk)] 
  = return (consCgStmt if_stmt blk)
  where
    cmm_lit = mkSimpleLit lit
    rep     = cmmLitRep cmm_lit
    cond    = CmmMachOp (MO_Ne rep) [scrut, CmmLit cmm_lit]
    if_stmt = CmmCondBranch cond deflt_blk_id

mk_lit_switch scrut deflt_blk_id branches
  = do	{ hi_blk <- mk_lit_switch scrut deflt_blk_id hi_branches
 	; lo_blk <- mk_lit_switch scrut deflt_blk_id lo_branches
	; lo_blk_id <- forkCgStmts lo_blk
	; let if_stmt = CmmCondBranch cond lo_blk_id
	; return (if_stmt `consCgStmt` hi_blk) }
  where
    n_branches = length branches
    (mid_lit,_) = branches !! (n_branches `div` 2)
	-- See notes above re mid_tag

    (lo_branches, hi_branches) = span is_lo branches
    is_lo (t,_) = t < mid_lit

    cond    = CmmMachOp (mkLtOp mid_lit) 
			[scrut, CmmLit (mkSimpleLit mid_lit)]

-------------------------------------------------------------------------
--
--	Simultaneous assignment
--
-------------------------------------------------------------------------


emitSimultaneously :: CmmStmts -> Code
-- Emit code to perform the assignments in the
-- input simultaneously, using temporary variables when necessary.
--
-- The Stmts must be:
--	CmmNop, CmmComment, CmmAssign, CmmStore
-- and nothing else


-- We use the strongly-connected component algorithm, in which
--	* the vertices are the statements
--	* an edge goes from s1 to s2 iff
--		s1 assigns to something s2 uses
--	  that is, if s1 should *follow* s2 in the final order

type CVertex = (Int, CmmStmt)	-- Give each vertex a unique number,
				-- for fast comparison

emitSimultaneously stmts
  = codeOnly $
    case filterOut isNopStmt (stmtList stmts) of 
	-- Remove no-ops
      []     	-> nopC
      [stmt] 	-> stmtC stmt	-- It's often just one stmt
      stmt_list -> doSimultaneously1 (zip [(1::Int)..] stmt_list)

doSimultaneously1 :: [CVertex] -> Code
doSimultaneously1 vertices
  = let
	edges = [ (vertex, key1, edges_from stmt1)
		| vertex@(key1, stmt1) <- vertices
		]
	edges_from stmt1 = [ key2 | (key2, stmt2) <- vertices, 
				    stmt1 `mustFollow` stmt2
			   ]
	components = stronglyConnComp edges

	-- do_components deal with one strongly-connected component
	-- Not cyclic, or singleton?  Just do it
	do_component (AcyclicSCC (n,stmt))  = stmtC stmt
	do_component (CyclicSCC [(n,stmt)]) = stmtC stmt

		-- Cyclic?  Then go via temporaries.  Pick one to
		-- break the loop and try again with the rest.
	do_component (CyclicSCC ((n,first_stmt) : rest))
	  = do	{ from_temp <- go_via_temp first_stmt
		; doSimultaneously1 rest
		; stmtC from_temp }

	go_via_temp (CmmAssign dest src)
	  = do	{ tmp <- newTemp (cmmRegRep dest)
		; stmtC (CmmAssign tmp src)
		; return (CmmAssign dest (CmmReg tmp)) }
	go_via_temp (CmmStore dest src)
	  = do	{ tmp <- newTemp (cmmExprRep src)
		; stmtC (CmmAssign tmp src)
		; return (CmmStore dest (CmmReg tmp)) }
    in
    mapCs do_component components

mustFollow :: CmmStmt -> CmmStmt -> Bool
CmmAssign reg _  `mustFollow` stmt = anySrc (reg `regUsedIn`) stmt
CmmStore loc e   `mustFollow` stmt = anySrc (locUsedIn loc (cmmExprRep e)) stmt
CmmNop           `mustFollow` stmt = False
CmmComment _     `mustFollow` stmt = False


anySrc :: (CmmExpr -> Bool) -> CmmStmt -> Bool
-- True if the fn is true of any input of the stmt
anySrc p (CmmAssign _ e)    = p e
anySrc p (CmmStore e1 e2)   = p e1 || p e2	-- Might be used in either side
anySrc p (CmmComment _)	    = False
anySrc p CmmNop		    = False
anySrc p other		    = True		-- Conservative

regUsedIn :: CmmReg -> CmmExpr -> Bool
reg `regUsedIn` CmmLit _ 	 = False
reg `regUsedIn` CmmLoad e  _ 	 = reg `regUsedIn` e
reg `regUsedIn` CmmReg reg' 	 = reg == reg'
reg `regUsedIn` CmmRegOff reg' _ = reg == reg'
reg `regUsedIn` CmmMachOp _ es   = any (reg `regUsedIn`) es

locUsedIn :: CmmExpr -> MachRep -> CmmExpr -> Bool
-- (locUsedIn a r e) checks whether writing to r[a] could affect the value of
-- 'e'.  Returns True if it's not sure.
locUsedIn loc rep (CmmLit _) 	     = False
locUsedIn loc rep (CmmLoad e ld_rep) = possiblySameLoc loc rep e ld_rep
locUsedIn loc rep (CmmReg reg')      = False
locUsedIn loc rep (CmmRegOff reg' _) = False
locUsedIn loc rep (CmmMachOp _ es)   = any (locUsedIn loc rep) es

possiblySameLoc :: CmmExpr -> MachRep -> CmmExpr -> MachRep -> Bool
-- Assumes that distinct registers (eg Hp, Sp) do not 
-- point to the same location, nor any offset thereof.
possiblySameLoc (CmmReg r1)       rep1 (CmmReg r2)      rep2  = r1==r2
possiblySameLoc (CmmReg r1)       rep1 (CmmRegOff r2 0) rep2  = r1==r2
possiblySameLoc (CmmRegOff r1 0)  rep1 (CmmReg r2)      rep2  = r1==r2
possiblySameLoc (CmmRegOff r1 start1) rep1 (CmmRegOff r2 start2) rep2 
  = r1==r2 && end1 > start2 && end2 > start1
  where
    end1 = start1 + machRepByteWidth rep1
    end2 = start2 + machRepByteWidth rep2

possiblySameLoc l1 rep1 (CmmLit _) rep2 = False
possiblySameLoc l1 rep1 l2	   rep2 = True	-- Conservative