CmmActuals -> -- zero or more arguments
CmmNode O O
-- Semantics: kills only result regs; all other regs (both GlobalReg
- -- and LocalReg) are preserved
+ -- and LocalReg) are preserved. But there is a current
+ -- bug for what can be put in arguments, see
+ -- Note [Register Parameter Passing]
CmmBranch :: Label -> CmmNode O C -- Goto another block in the same procedure
-- moment of the call. Later stages can use this to give liveness
-- everywhere, which in turn guides register allocation.
-- It is the companion of cml_args; cml_args says which stack words
--- hold parameters, while cml_arg_regs says which global regs hold parameters
+-- hold parameters, while cml_arg_regs says which global regs hold parameters.
+-- But do note [Register parameter passing]
cml_args :: ByteOff,
-- Byte offset, from the *old* end of the Area associated with
-- Always the last node of a block
tgt :: ForeignTarget, -- call target and convention
res :: CmmFormals, -- zero or more results
- args :: CmmActuals, -- zero or more arguments
+ args :: CmmActuals, -- zero or more arguments; see Note [Register parameter passing]
succ :: Label, -- Label of continuation
updfr :: UpdFrameOffset, -- where the update frame is (for building infotable)
intrbl:: Bool -- whether or not the call is interruptible
~~~~~~~~~~~~~~~~~~~~~~~
A CmmUnsafeForeignCall is used for *unsafe* foreign calls;
a CmmForeignCall call is used for *safe* foreign calls.
-Unsafe ones are easy: think of them as a "fat machine instruction".
-In particular, they do *not* kill all live registers (there was a bit
-of code in GHC that conservatively assumed otherwise.)
+
+Unsafe ones are mostly easy: think of them as a "fat machine
+instruction". In particular, they do *not* kill all live registers,
+just the registers they return to (there was a bit of code in GHC that
+conservatively assumed otherwise.) However, see [Register parameter passing].
Safe ones are trickier. A safe foreign call
r = f(x)
Note that a safe foreign call needs an info table.
-}
+{- Note [Register parameter passing]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+On certain architectures, some registers are utilized for parameter
+passing in the C calling convention. For example, in x86-64 Linux
+convention, rdi, rsi, rdx and rcx (as well as r8 and r9) may be used for
+argument passing. These are registers R3-R6, which our generated
+code may also be using; as a result, it's necessary to save these
+values before doing a foreign call. This is done during initial
+code generation in callerSaveVolatileRegs in StgCmmUtils.hs. However,
+one result of doing this is that the contents of these registers
+may mysteriously change if referenced inside the arguments. This
+is dangerous, so you'll need to disable inlining much in the same
+way is done in cmm/CmmOpt.hs currently. We should fix this!
+-}
+
---------------------------------------------
-- Eq instance of CmmNode
-- It is a shame GHC cannot infer it by itself :(
import CmmExpr
import CmmLive
import OptimizationFuel
+import StgCmmUtils
import Control.Monad
import Outputable hiding (empty)
-}
-- Assumption: Unsafe foreign calls don't clobber memory
+-- Since foreign calls clobber caller saved registers, we need
+-- invalidate any assignments that reference those global registers.
+-- This is kind of expensive. (One way to optimize this might be to
+-- store extra information about expressions that allow this and other
+-- checks to be done cheaply.)
middleAssignment (Plain n@(CmmUnsafeForeignCall{})) assign
- = foldRegsDefd (\m r -> addToUFM m r NeverOptimize) (deleteSinks n assign) n
+ = deleteCallerSaves (foldRegsDefd (\m r -> addToUFM m r NeverOptimize) (deleteSinks n assign) n)
+ where deleteCallerSaves m = foldUFM_Directly f m m
+ f u (xassign -> Just x) m | wrapRecExpf g x False = addToUFM_Directly m u NeverOptimize
+ f _ _ m = m
+ g (CmmReg (CmmGlobal r)) _ | callerSaves r = True
+ g (CmmRegOff (CmmGlobal r) _) _ | callerSaves r = True
+ g _ b = b
middleAssignment (Plain (CmmComment {})) assign
= assign
Nothing -> (i, l)
rewrite _ (False, []) _ _ = Nothing
-- Note [CmmCall Inline Hack]
- -- ToDo: Conservative hack: don't do any inlining on CmmCalls, since
- -- the code produced here tends to be unproblematic and I need
- -- to write lint passes to ensure that we don't put anything in
- -- the arguments that could be construed as a global register by
+ -- Conservative hack: don't do any inlining on what will
+ -- be translated into an OldCmm CmmCalls, since the code
+ -- produced here tends to be unproblematic and I need to write
+ -- lint passes to ensure that we don't put anything in the
+ -- arguments that could be construed as a global register by
-- some later translation pass. (For example, slots will turn
- -- into dereferences of Sp). This is the same hack in spirit as
- -- was in cmm/CmmOpt.hs. Fix this up to only bug out if certain
- -- CmmExprs are involved.
- -- ToDo: We miss an opportunity here, where all possible
- -- inlinings should instead be sunk.
+ -- into dereferences of Sp). See [Register parameter passing].
+ -- ToDo: Fix this up to only bug out if all inlines were for
+ -- CmmExprs with global registers (we can't use the
+ -- straightforward mapExpDeep call, in this case.) ToDo: We miss
+ -- an opportunity here, where all possible inlinings should
+ -- instead be sunk.
rewrite _ (True, []) _ n | not (inlinable n) = Nothing -- see [CmmCall Inline Hack]
rewrite assign (i, xs) mk n = Just $ mkMiddles xs <*> mk (Plain (inline i assign n))
inlinable :: CmmNode e x -> Bool
inlinable (CmmCall{}) = False
inlinable (CmmForeignCall{}) = False
+ inlinable (CmmUnsafeForeignCall{}) = False
inlinable _ = True
rewriteAssignments :: CmmGraph -> FuelUniqSM CmmGraph
| CmmStore CmmExpr CmmExpr -- Assign to memory location. Size is
-- given by cmmExprType of the rhs.
- | CmmCall -- A call (forign, native or primitive), with
+ | CmmCall -- A call (foreign, native or primitive), with
CmmCallTarget
HintedCmmFormals -- zero or more results
HintedCmmActuals -- zero or more arguments
CmmSafety -- whether to build a continuation
CmmReturnInfo
+ -- Some care is necessary when handling the arguments of these, see
+ -- [Register parameter passing] and the hack in cmm/CmmOpt.hs
| CmmBranch BlockId -- branch to another BB in this fn
-- * Regs.h claims that BaseReg should be saved last and loaded first
-- * This might not have been tickled before since BaseReg is callee save
-- * Regs.h saves SparkHd, ParkT1, SparkBase and SparkLim
+-- EZY: This code is very dodgy, because callerSaves only ever
+-- returns true in the current universe for registers NOT in
+-- system_regs (just do a grep for CALLER_SAVES in
+-- includes/stg/MachRegs.h). Thus, this is all one giant no-op. What we are
+-- actually interested in is saving are the non-system registers, which
+-- we is what the old code generator actually does at this point.
+-- Unfortunately, we can't do that here either, because we don't
+-- liveness information, and thus there's not an easy way to tell which
+-- specific global registers need to be saved (the 'vols' argument in
+-- the old code generator.) One possible hack is to save all of them
+-- unconditionally, but unless we have very clever dead /memory/
+-- elimination (unlikely), this will still leave a dead, unnecessary
+-- memory assignment. And really, we shouldn't be doing the workaround
+-- at this point in the pipeline, see Note [Register parameter passing].
+-- Right now the workaround is to avoid inlining across unsafe foreign
+-- calls in rewriteAssignments.
callerSaveVolatileRegs :: (CmmAGraph, CmmAGraph)
callerSaveVolatileRegs = (caller_save, caller_load)
where
#ifdef CALLER_SAVES_Base
callerSaves BaseReg = True
#endif
+#ifdef CALLER_SAVES_R1
+callerSaves (VanillaReg 1 _) = True
+#endif
+#ifdef CALLER_SAVES_R2
+callerSaves (VanillaReg 2 _) = True
+#endif
+#ifdef CALLER_SAVES_R3
+callerSaves (VanillaReg 3 _) = True
+#endif
+#ifdef CALLER_SAVES_R4
+callerSaves (VanillaReg 4 _) = True
+#endif
+#ifdef CALLER_SAVES_R5
+callerSaves (VanillaReg 5 _) = True
+#endif
+#ifdef CALLER_SAVES_R6
+callerSaves (VanillaReg 6 _) = True
+#endif
+#ifdef CALLER_SAVES_R7
+callerSaves (VanillaReg 7 _) = True
+#endif
+#ifdef CALLER_SAVES_R8
+callerSaves (VanillaReg 8 _) = True
+#endif
+#ifdef CALLER_SAVES_F1
+callerSaves (FloatReg 1) = True
+#endif
+#ifdef CALLER_SAVES_F2
+callerSaves (FloatReg 2) = True
+#endif
+#ifdef CALLER_SAVES_F3
+callerSaves (FloatReg 3) = True
+#endif
+#ifdef CALLER_SAVES_F4
+callerSaves (FloatReg 4) = True
+#endif
+#ifdef CALLER_SAVES_D1
+callerSaves (DoubleReg 1) = True
+#endif
+#ifdef CALLER_SAVES_D2
+callerSaves (DoubleReg 2) = True
+#endif
+#ifdef CALLER_SAVES_L1
+callerSaves (LongReg 1) = True
+#endif
#ifdef CALLER_SAVES_Sp
callerSaves Sp = True
#endif
Caller-saves regs have to be saved around C-calls made from STG
land, so this file defines CALLER_SAVES_<reg> for each <reg> that
is designated caller-saves in that machine's C calling convention.
+
+ As it stands, the only registers that are ever marked caller saves
+ are the RX, FX, DX and USER registers; as a result, if you
+ decide to caller save a system register (e.g. SP, HP, etc), note that
+ this code path is completely untested! -- EZY
-------------------------------------------------------------------------- */
/* -----------------------------------------------------------------------------
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