LLVM: Implement atomic operations in terms of LLVM primitives

This fixes Trac #7883.

This adds proper support for,
  * `MO_AtomicRMW`
  * `MO_AtomicWrite`
  * `MO_CmpXChg`

Test Plan: Validate

Reviewers: rrnewton, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1282

GHC Trac Issues: #7883

3 files changed, 67 insertions, 3 deletions

diff --git a/compiler/llvmGen/Llvm/AbsSyn.hs b/compiler/llvmGen/Llvm/AbsSyn.hs
index 8a53df00fe..774e555170 100644
--- a/compiler/llvmGen/Llvm/AbsSyn.hs
+++ b/compiler/llvmGen/Llvm/AbsSyn.hs
@@ -87,6 +87,22 @@ data LlvmSyncOrdering
   | SyncSeqCst
   deriving (Show, Eq)
 
+-- | LLVM atomic operations. Please see the @atomicrmw@ instruction in
+-- the LLVM documentation for a complete description.
+data LlvmAtomicOp
+  = LAO_Xchg
+  | LAO_Add
+  | LAO_Sub
+  | LAO_And
+  | LAO_Nand
+  | LAO_Or
+  | LAO_Xor
+  | LAO_Max
+  | LAO_Min
+  | LAO_Umax
+  | LAO_Umin
+  deriving (Show, Eq)
+
 -- | Llvm Statements
 data LlvmStatement
   {- |
@@ -250,8 +266,8 @@ data LlvmExpression
   | GetElemPtr Bool LlvmVar [LlvmVar]
 
   {- |
-     Cast the variable from to the to type. This is an abstraction of three
-     cast operators in Llvm, inttoptr, prttoint and bitcast.
+    Cast the variable from to the to type. This is an abstraction of three
+    cast operators in Llvm, inttoptr, prttoint and bitcast.
        * cast: Cast type
        * from: Variable to cast
        * to:   type to cast to
@@ -259,6 +275,28 @@ data LlvmExpression
   | Cast LlvmCastOp LlvmVar LlvmType
 
   {- |
+    Atomic read-modify-write operation
+       * op:       Atomic operation
+       * addr:     Address to modify
+       * operand:  Operand to operation
+       * ordering: Ordering requirement
+  -}
+  | AtomicRMW LlvmAtomicOp LlvmVar LlvmVar LlvmSyncOrdering
+
+  {- |
+    Compare-and-exchange operation
+       * addr:     Address to modify
+       * old:      Expected value
+       * new:      New value
+       * suc_ord:  Ordering required in success case
+       * fail_ord: Ordering required in failure case, can be no stronger than
+                   suc_ord
+
+    Result is an @i1@, true if store was successful.
+  -}
+  | CmpXChg LlvmVar LlvmVar LlvmVar LlvmSyncOrdering LlvmSyncOrdering
+
+  {- |
     Call a function. The result is the value of the expression.
       * tailJumps: CallType to signal if the function should be tail called
       * fnptrval:  An LLVM value containing a pointer to a function to be
diff --git a/compiler/llvmGen/Llvm/PpLlvm.hs b/compiler/llvmGen/Llvm/PpLlvm.hs
index db9ef1fccf..8476b9d585 100644
--- a/compiler/llvmGen/Llvm/PpLlvm.hs
+++ b/compiler/llvmGen/Llvm/PpLlvm.hs
@@ -245,6 +245,8 @@ ppLlvmExpression expr
         Load       ptr              -> ppLoad ptr
         ALoad      ord st ptr       -> ppALoad ord st ptr
         Malloc     tp amount        -> ppMalloc tp amount
+        AtomicRMW  aop tgt src ordering -> ppAtomicRMW aop tgt src ordering
+        CmpXChg    addr old new s_ord f_ord -> ppCmpXChg addr old new s_ord f_ord
         Phi        tp precessors    -> ppPhi tp precessors
         Asm        asm c ty v se sk -> ppAsm asm c ty v se sk
         MExpr      meta expr        -> ppMetaExpr meta expr
@@ -327,6 +329,30 @@ ppSyncOrdering SyncRelease   = text "release"
 ppSyncOrdering SyncAcqRel    = text "acq_rel"
 ppSyncOrdering SyncSeqCst    = text "seq_cst"
 
+ppAtomicOp :: LlvmAtomicOp -> SDoc
+ppAtomicOp LAO_Xchg = text "xchg"
+ppAtomicOp LAO_Add  = text "add"
+ppAtomicOp LAO_Sub  = text "sub"
+ppAtomicOp LAO_And  = text "and"
+ppAtomicOp LAO_Nand = text "nand"
+ppAtomicOp LAO_Or   = text "or"
+ppAtomicOp LAO_Xor  = text "xor"
+ppAtomicOp LAO_Max  = text "max"
+ppAtomicOp LAO_Min  = text "min"
+ppAtomicOp LAO_Umax = text "umax"
+ppAtomicOp LAO_Umin = text "umin"
+
+ppAtomicRMW :: LlvmAtomicOp -> LlvmVar -> LlvmVar -> LlvmSyncOrdering -> SDoc
+ppAtomicRMW aop tgt src ordering =
+  text "atomicrmw" <+> ppAtomicOp aop <+> ppr tgt <> comma
+  <+> ppr src <+> ppSyncOrdering ordering
+
+ppCmpXChg :: LlvmVar -> LlvmVar -> LlvmVar
+          -> LlvmSyncOrdering -> LlvmSyncOrdering -> SDoc
+ppCmpXChg addr old new s_ord f_ord =
+  text "cmpxchg" <+> ppr addr <> comma <+> ppr old <> comma <+> ppr new
+  <+> ppSyncOrdering s_ord <+> ppSyncOrdering f_ord
+
 -- XXX: On x86, vector types need to be 16-byte aligned for aligned access, but
 -- we have no way of guaranteeing that this is true with GHC (we would need to
 -- modify the layout of the stack and closures, change the storage manager,
diff --git a/compiler/llvmGen/Llvm/Types.hs b/compiler/llvmGen/Llvm/Types.hs
index b3b173096b..9780bf39cf 100644
--- a/compiler/llvmGen/Llvm/Types.hs
+++ b/compiler/llvmGen/Llvm/Types.hs
@@ -262,7 +262,7 @@ pLift LMVoid     = error "Voids are unliftable"
 pLift LMMetadata = error "Metadatas are unliftable"
 pLift x          = LMPointer x
 
--- | Lower a variable of 'LMPointer' type.
+-- | Lift a variable to 'LMPointer' type.
 pVarLift :: LlvmVar -> LlvmVar
 pVarLift (LMGlobalVar s t l x a c) = LMGlobalVar s (pLift t) l x a c
 pVarLift (LMLocalVar  s t        ) = LMLocalVar  s (pLift t)