Deprecate -fllvm-pass-vectors-in-regs

Summary:
The behavior previously enabled by this flag is as been the default
since 8.6.1.

Reviewers: simonmar

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5193

3 files changed, 12 insertions, 17 deletions

diff --git a/compiler/cmm/CmmCallConv.hs b/compiler/cmm/CmmCallConv.hs
index e1067e9519..f338415adc 100644
--- a/compiler/cmm/CmmCallConv.hs
+++ b/compiler/cmm/CmmCallConv.hs
@@ -102,19 +102,12 @@ passFloatArgsInXmm dflags = case platformArch (targetPlatform dflags) of
                               ArchX86_64 -> True
                               _          -> False
 
--- On X86_64, we always pass 128-bit-wide vectors in registers. On 32-bit X86
--- and for all larger vector sizes on X86_64, LLVM's GHC calling convention
--- does not currently pass vectors in registers. The patch to update the GHC
--- calling convention to support passing SIMD vectors in registers is small and
--- well-contained, so it may make it into LLVM 3.4. The hidden
--- -fllvm-pass-vectors-in-regs flag will generate LLVM code that attempts to
--- pass vectors in registers, but it must only be used with a version of LLVM
--- that has an updated GHC calling convention.
+-- We used to spill vector registers to the stack since the LLVM backend didn't
+-- support vector registers in its calling convention. However, this has now
+-- been fixed. This function remains only as a convenient way to re-enable
+-- spilling when debugging code generation.
 passVectorInReg :: Width -> DynFlags -> Bool
-passVectorInReg W128 dflags = case platformArch (targetPlatform dflags) of
-                                ArchX86_64 -> True
-                                _          -> gopt Opt_LlvmPassVectorsInRegisters dflags
-passVectorInReg _    dflags = gopt Opt_LlvmPassVectorsInRegisters dflags
+passVectorInReg _ _ = True
 
 assignStack :: DynFlags -> ByteOff -> (a -> CmmType) -> [a]
             -> (
diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index 2c8f13418e..3a14b29806 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -474,7 +474,6 @@ data GeneralFlag
    | Opt_RegsIterative                  -- do iterative coalescing graph coloring register allocation
    | Opt_PedanticBottoms                -- Be picky about how we treat bottom
    | Opt_LlvmTBAA                       -- Use LLVM TBAA infastructure for improving AA (hidden flag)
-   | Opt_LlvmPassVectorsInRegisters     -- Pass SIMD vectors in registers (requires a patched LLVM) (hidden flag)
    | Opt_LlvmFillUndefWithGarbage       -- Testing for undef bugs (hidden flag)
    | Opt_IrrefutableTuples
    | Opt_CmmSink
@@ -680,7 +679,6 @@ optimisationFlags = EnumSet.fromList
    , Opt_RegsIterative
    , Opt_PedanticBottoms
    , Opt_LlvmTBAA
-   , Opt_LlvmPassVectorsInRegisters
    , Opt_LlvmFillUndefWithGarbage
    , Opt_IrrefutableTuples
    , Opt_CmmSink
@@ -3380,6 +3378,9 @@ dynamic_flags_deps = [
   , make_ord_flag defFlag "fno-refinement-level-hole-fits"
       (noArg (\d -> d { refLevelHoleFits = Nothing }))
 
+  , make_dep_flag defGhcFlag "fllvm-pass-vectors-in-regs"
+            (noArg id)
+            "vectors registers are now passed in registers by default."
   , make_ord_flag defFlag "fmax-uncovered-patterns"
       (intSuffix (\n d -> d { maxUncoveredPatterns = n }))
   , make_ord_flag defFlag "fsimplifier-phases"
@@ -3957,7 +3958,6 @@ fFlagsDeps = [
   flagSpec "late-dmd-anal"                    Opt_LateDmdAnal,
   flagSpec "late-specialise"                  Opt_LateSpecialise,
   flagSpec "liberate-case"                    Opt_LiberateCase,
-  flagSpec "llvm-pass-vectors-in-regs"        Opt_LlvmPassVectorsInRegisters,
   flagHiddenSpec "llvm-tbaa"                  Opt_LlvmTBAA,
   flagHiddenSpec "llvm-fill-undef-with-garbage" Opt_LlvmFillUndefWithGarbage,
   flagSpec "loopification"                    Opt_Loopification,
@@ -4283,8 +4283,7 @@ defaultFlags settings
       Opt_RPath,
       Opt_SharedImplib,
       Opt_SimplPreInlining,
-      Opt_VersionMacros,
-      Opt_LlvmPassVectorsInRegisters
+      Opt_VersionMacros
     ]
 
     ++ [f | (ns,f) <- optLevelFlags, 0 `elem` ns]
diff --git a/docs/users_guide/8.8.1-notes.rst b/docs/users_guide/8.8.1-notes.rst
index 4de2369313..37bad13b5b 100644
--- a/docs/users_guide/8.8.1-notes.rst
+++ b/docs/users_guide/8.8.1-notes.rst
@@ -61,6 +61,9 @@ Compiler
 
 - The :ghc-flag:`-Wcompat` warning group now includes :ghc-flag:`-Wstar-is-type`.
 
+- The :ghc-flag:`-fllvm-pass-vectors-in-regs` flag is now deprecated as vector
+  arguments are now passed in registers by default.
+
 Runtime system
 ~~~~~~~~~~~~~~