Commit 03341842 authored by simonmar's avatar simonmar

[project @ 2005-11-08 12:56:04 by simonmar]

gcc's -fstrict-aliasing is biting us when we use the stack to store
different types of objects.  For example:

  *((StgDouble*)((W_)Sp-8)) = *((StgDouble*)((W_)Sp+8));
  Sp[1] = (W_)&s1Cx_info;

gcc feels free to reorder these two lines, because they refer to
differently typed objects, even though the assignment to Sp[1] clearly
aliases the read from the same location.

Trying to fix this by accessing locations using union types might be
possible, but I took the sledgehammer approach of
-fno-strict-aliasing.  This is justified to a certain extent because
our generated C code is derived from a very weakly-typed internal
language (C--).
parent 27249023
......@@ -852,6 +852,23 @@ runPhase cc_phase stop dflags basename suff input_fn get_output_fn maybe_loc
| otherwise = As
output_fn <- get_output_fn next_phase maybe_loc
let
more_hcc_opts =
#if x86_TARGET_ARCH
-- on x86 the floating point regs have greater precision
-- than a double, which leads to unpredictable results.
-- By default, we turn this off with -ffloat-store unless
-- the user specified -fexcess-precision.
(if excessPrecision then [] else [ "-ffloat-store" ]) ++
#endif
-- gcc's -fstrict-aliasing allows two accesses to memory
-- to be considered non-aliasing if they have different types.
-- This interacts badly with the C code we generate, which is
-- very weakly typed, being derived from C--.
["-fno-strict-aliasing"]
SysTools.runCc dflags (
-- force the C compiler to interpret this file as C when
-- compiling .hc files, by adding the -x c option.
......@@ -868,13 +885,13 @@ runPhase cc_phase stop dflags basename suff input_fn get_output_fn maybe_loc
++ (if hcc && mangle
then md_regd_c_flags
else [])
++ (if hcc
then more_hcc_opts
else [])
++ [ verb, "-S", "-Wimplicit", "-O" ]
++ [ "-D__GLASGOW_HASKELL__="++cProjectVersionInt ]
++ cc_opts
++ split_opt
#if x86_TARGET_ARCH
++ (if excessPrecision then [] else [ "-ffloat-store" ])
#endif
++ include_paths
++ pkg_extra_cc_opts
))
......
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