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| author | Joachim Breitner <mail@joachim-breitner.de> | 2015-03-02 21:20:24 +0100 |
|---|---|---|
| committer | Joachim Breitner <mail@joachim-breitner.de> | 2015-03-02 23:12:46 +0100 |
| commit | c3eee14d31585445d4a7eff5b6c69a815b911059 (patch) | |
| tree | 052db8973e5fe2c1e4ce823f6f2b267b86dd8d8c /compiler/codeGen/StgCmmUtils.hs | |
| parent | 3197018d4efbf7407577300b88897cef26f7f4c6 (diff) | |
| download | haskell-c3eee14d31585445d4a7eff5b6c69a815b911059.tar.gz | |
Improve if-then-else tree for cases on literal values
Previously, in the branch of the if-then-else tree, it would emit a
final check if the scrut matches the alternative, even if earlier
comparisons alread imply this equality. By keeping track of the bounds
we can skip this check. Of course this is only sound for integer types.
This closes #10129.
Differential Revision: https://phabricator.haskell.org/D693
Diffstat (limited to 'compiler/codeGen/StgCmmUtils.hs')
| -rw-r--r-- | compiler/codeGen/StgCmmUtils.hs | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/compiler/codeGen/StgCmmUtils.hs b/compiler/codeGen/StgCmmUtils.hs index 5e8944df4a..763177f297 100644 --- a/compiler/codeGen/StgCmmUtils.hs +++ b/compiler/codeGen/StgCmmUtils.hs @@ -652,14 +652,21 @@ emitCmmLitSwitch scrut branches deflt = do join_lbl <- newLabelC deflt_lbl <- label_code join_lbl deflt branches_lbls <- label_branches join_lbl branches - emit =<< mk_lit_switch scrut' deflt_lbl + emit =<< mk_lit_switch scrut' deflt_lbl noBound (sortBy (comparing fst) branches_lbls) emitLabel join_lbl +-- | lower bound (inclusive), upper bound (exclusive) +type LitBound = (Maybe Literal, Maybe Literal) + +noBound :: LitBound +noBound = (Nothing, Nothing) + mk_lit_switch :: CmmExpr -> BlockId + -> LitBound -> [(Literal,BlockId)] -> FCode CmmAGraph -mk_lit_switch scrut deflt [(lit,blk)] +mk_lit_switch scrut deflt bounds [(lit,blk)] = do dflags <- getDynFlags let @@ -667,12 +674,19 @@ mk_lit_switch scrut deflt [(lit,blk)] cmm_ty = cmmLitType dflags cmm_lit rep = typeWidth cmm_ty ne = if isFloatType cmm_ty then MO_F_Ne rep else MO_Ne rep - return (mkCbranch (CmmMachOp ne [scrut, CmmLit cmm_lit]) deflt blk) -mk_lit_switch scrut deflt_blk_id branches + return $ if lit `onlyWithinBounds'` bounds + then mkBranch blk + else mkCbranch (CmmMachOp ne [scrut, CmmLit cmm_lit]) deflt blk + where + -- If the bounds already imply scrut == lit, then we can skip the final check (#10129) + l `onlyWithinBounds'` (Just lo, Just hi) = l `onlyWithinBounds` (lo, hi) + l `onlyWithinBounds'` _ = False + +mk_lit_switch scrut deflt_blk_id (lo_bound, hi_bound) branches = do dflags <- getDynFlags - lo_blk <- mk_lit_switch scrut deflt_blk_id lo_branches - hi_blk <- mk_lit_switch scrut deflt_blk_id hi_branches + lo_blk <- mk_lit_switch scrut deflt_blk_id bounds_lo lo_branches + hi_blk <- mk_lit_switch scrut deflt_blk_id bounds_hi hi_branches mkCmmIfThenElse (cond dflags) lo_blk hi_blk where n_branches = length branches @@ -682,6 +696,9 @@ mk_lit_switch scrut deflt_blk_id branches (lo_branches, hi_branches) = span is_lo branches is_lo (t,_) = t < mid_lit + bounds_lo = (lo_bound, Just mid_lit) + bounds_hi = (Just mid_lit, hi_bound) + cond dflags = CmmMachOp (mkLtOp dflags mid_lit) [scrut, CmmLit (mkSimpleLit dflags mid_lit)] |