When generating a switch for:
case e of
0 -> A
1 -> B
instead of generating
if (e < 1) then goto A
B
generate
if (e >= 1) then goto B
A
because this helps the NCG to generate better code. In particular, if
e is a comparison, then we don't need to reverse the sense of the
comparison to eliminate the comparse against 1 (the NCG does try to
reverse the comparison, but floating-point comparisons can't be
reversed).
import CmmUtils
import MachOp ( MachRep(..), wordRep, MachOp(..), MachHint(..),
mo_wordOr, mo_wordAnd, mo_wordNe, mo_wordEq,
import CmmUtils
import MachOp ( MachRep(..), wordRep, MachOp(..), MachHint(..),
mo_wordOr, mo_wordAnd, mo_wordNe, mo_wordEq,
- mo_wordULt, mo_wordUGt, machRepByteWidth )
+ mo_wordULt, mo_wordUGt, mo_wordUGe, machRepByteWidth )
import ForeignCall ( CCallConv(..) )
import Literal ( Literal(..) )
import CLabel ( CLabel, mkStringLitLabel )
import ForeignCall ( CCallConv(..) )
import Literal ( Literal(..) )
import CLabel ( CLabel, mkStringLitLabel )
cmmNeWord e1 e2 = CmmMachOp mo_wordNe [e1, e2]
cmmEqWord e1 e2 = CmmMachOp mo_wordEq [e1, e2]
cmmULtWord e1 e2 = CmmMachOp mo_wordULt [e1, e2]
cmmNeWord e1 e2 = CmmMachOp mo_wordNe [e1, e2]
cmmEqWord e1 e2 = CmmMachOp mo_wordEq [e1, e2]
cmmULtWord e1 e2 = CmmMachOp mo_wordULt [e1, e2]
+cmmUGeWord e1 e2 = CmmMachOp mo_wordUGe [e1, e2]
cmmUGtWord e1 e2 = CmmMachOp mo_wordUGt [e1, e2]
cmmNegate :: CmmExpr -> CmmExpr
cmmUGtWord e1 e2 = CmmMachOp mo_wordUGt [e1, e2]
cmmNegate :: CmmExpr -> CmmExpr
lo_tag (mid_tag-1) via_C
; hi_stmts <- mk_switch tag_expr' hi_branches mb_deflt
mid_tag hi_tag via_C
lo_tag (mid_tag-1) via_C
; hi_stmts <- mk_switch tag_expr' hi_branches mb_deflt
mid_tag hi_tag via_C
- ; lo_id <- forkCgStmts lo_stmts
- ; let cond = cmmULtWord tag_expr' (CmmLit (mkIntCLit mid_tag))
- branch_stmt = CmmCondBranch cond lo_id
- ; return (assign_tag `consCgStmt` (branch_stmt `consCgStmt` hi_stmts))
+ ; 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))
+ -- 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).
where
use_switch = {- pprTrace "mk_switch" (
ppr tag_expr <+> text "n_tags:" <+> int n_tags <+>
where
use_switch = {- pprTrace "mk_switch" (
ppr tag_expr <+> text "n_tags:" <+> int n_tags <+>