#10555: RULE left-hand side too complicated to desugar -------------------------------------+------------------------------------- Reporter: yongqli | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.0.4 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: yes Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by thomie): * related: #10699 => Old description:
GHC reports the following warnings for the `fast-math` package. To reproduce, run `cabal install fast-math==1.0 --with-ghc=ghc-7.10.1` (ghc-7.10.2 panics on this package, see #10699).
{{{
Numeric/FastMath/Approximation.hs:60:1: Warning: RULE left-hand side too complicated to desugar Optimised lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_X2 { __DEFAULT -> +## wild_X2 }) wild_00 } Orig lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_00 { __DEFAULT -> +## wild_00 }) wild_00 }
Numeric/FastMath/Approximation.hs:63:1: Warning: RULE left-hand side too complicated to desugar Optimised lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_X2 { __DEFAULT -> -## wild_X2 }) wild_00 } Orig lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_00 { __DEFAULT -> -## wild_00 }) wild_00 }
Numeric/FastMath/Approximation.hs:103:1: Warning: RULE left-hand side too complicated to desugar Optimised lhs: case divideFloat# y2 x of wild_00 { __DEFAULT -> (case divideFloat# y1 x of wild_X2 { __DEFAULT -> minusFloat# wild_X2 }) wild_00 } Orig lhs: case divideFloat# y2 x of wild_00 { __DEFAULT -> (case divideFloat# y1 x of wild_00 { __DEFAULT -> minusFloat# wild_00 }) wild_00 } }}}
New description: GHC reports multiple "RULE left-hand side too complicated to desugar" warnings for the `fast-math` package. Here is an testcase, extracted from `fast- math/Numeric/FastMath/Approximation.hs`: {{{ {-# LANGUAGE MagicHash #-} module T10555 where import GHC.Exts {-# RULES "double /,+ distribute" forall x y1 y2. (y1 /## x) +## (y2 /## x) = (y1 +## y2) /## x "double /,- distribute" forall x y1 y2. (y1 /## x) -## (y2 /## x) = (y1 -## y2) /## x "float /,- distribute" forall x y1 y2. (y1 `divideFloat#` x) `minusFloat#` (y2 `divideFloat#` x) = (y1 `minusFloat#` y2) `divideFloat#` x #-} }}} {{{ 2$ ghc-7.10.2 T10555.hs -fforce-recomp [1 of 1] Compiling T10555 ( T10555.hs, T10555.o ) T10555.hs:8:1: Warning: RULE left-hand side too complicated to desugar Optimised lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_X2 { __DEFAULT -> +## wild_X2 }) wild_00 } Orig lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_00 { __DEFAULT -> +## wild_00 }) wild_00 } T10555.hs:11:1: Warning: RULE left-hand side too complicated to desugar Optimised lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_X2 { __DEFAULT -> -## wild_X2 }) wild_00 } Orig lhs: case /## y2 x of wild_00 { __DEFAULT -> (case /## y1 x of wild_00 { __DEFAULT -> -## wild_00 }) wild_00 } T10555.hs:14:1: Warning: RULE left-hand side too complicated to desugar Optimised lhs: case divideFloat# y2 x of wild_00 { __DEFAULT -> (case divideFloat# y1 x of wild_X2 { __DEFAULT -> minusFloat# wild_X2 }) wild_00 } Orig lhs: case divideFloat# y2 x of wild_00 { __DEFAULT -> (case divideFloat# y1 x of wild_00 { __DEFAULT -> minusFloat# wild_00 }) wild_00 } }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10555#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler