Add '-fllvm-tbaa' flag for controlling LLVM TBAA opt.

compiler/main/DriverPipeline.hs

@@ -1306,15 +1306,18 @@ runPhase SplitAs _input_fn dflags
 
 runPhase LlvmOpt input_fn dflags
   = do
-    let lo_opts = getOpts dflags opt_lo
-    let opt_lvl = max 0 (min 2 $ optLevel dflags)
-    -- don't specify anything if user has specified commands. We do this for
-    -- opt but not llc since opt is very specifically for optimisation passes
-    -- only, so if the user is passing us extra options we assume they know
-    -- what they are doing and don't get in the way.
-    let optFlag = if null lo_opts
-                     then [SysTools.Option (llvmOpts !! opt_lvl)]
-                     else []
+    let lo_opts  = getOpts dflags opt_lo
+        opt_lvl  = max 0 (min 2 $ optLevel dflags)
+        -- don't specify anything if user has specified commands. We do this
+        -- for opt but not llc since opt is very specifically for optimisation
+        -- passes only, so if the user is passing us extra options we assume
+        -- they know what they are doing and don't get in the way.
+        optFlag  = if null lo_opts
+                       then [SysTools.Option (llvmOpts !! opt_lvl)]
+                       else []
+        tbaa | dopt Opt_LlvmTBAA dflags = "--enable-tbaa=true"
+             | otherwise                = "--enable-tbaa=false"
+
 
     output_fn <- phaseOutputFilename LlvmLlc
 
@@ -1323,6 +1326,7 @@ runPhase LlvmOpt input_fn dflags
                     SysTools.Option "-o",
                     SysTools.FileOption "" output_fn]
                 ++ optFlag
+                ++ [SysTools.Option tbaa]
                 ++ map SysTools.Option lo_opts)
 
     return (LlvmLlc, output_fn)
@@ -1341,6 +1345,8 @@ runPhase LlvmLlc input_fn dflags
         rmodel | opt_PIC        = "pic"
                | not opt_Static = "dynamic-no-pic"
                | otherwise      = "static"
+        tbaa | dopt Opt_LlvmTBAA dflags = "--enable-tbaa=true"
+             | otherwise                = "--enable-tbaa=false"
 
     -- hidden debugging flag '-dno-llvm-mangler' to skip mangling
     let next_phase = case dopt Opt_NoLlvmMangler dflags of
@@ -1356,6 +1362,7 @@ runPhase LlvmLlc input_fn dflags
                     SysTools.FileOption "" input_fn,
                     SysTools.Option "-o", SysTools.FileOption "" output_fn]
                 ++ map SysTools.Option lc_opts
+                ++ [SysTools.Option tbaa]
                 ++ map SysTools.Option fpOpts)
 
     return (next_phase, output_fn)
@@ -1373,7 +1380,7 @@ runPhase LlvmLlc input_fn dflags
                                       else if (elem VFPv3D16 ext)
                                            then ["-mattr=+v7,+vfp3,+d16"]
                                            else []
-                   _               -> []
+                   _                 -> []
 
 -----------------------------------------------------------------------------
 -- LlvmMangle phase

compiler/main/DynFlags.hs

@@ -250,6 +250,7 @@ data DynFlag
    | Opt_RegsGraph                      -- do graph coloring register allocation
    | 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
 
    -- Interface files
    | Opt_IgnoreInterfacePragmas
@@ -1823,6 +1824,7 @@ fFlags = [
   ( "vectorise",                        Opt_Vectorise, nop ),
   ( "regs-graph",                       Opt_RegsGraph, nop ),
   ( "regs-iterative",                   Opt_RegsIterative, nop ),
+  ( "llvm-tbaa",                        Opt_LlvmTBAA, nop),
   ( "gen-manifest",                     Opt_GenManifest, nop ),
   ( "embed-manifest",                   Opt_EmbedManifest, nop ),
   ( "ext-core",                         Opt_EmitExternalCore, nop ),
@@ -2071,6 +2073,7 @@ optLevelFlags
     , ([2],     Opt_LiberateCase)
     , ([2],     Opt_SpecConstr)
     , ([2],     Opt_RegsGraph)
+    , ([0,1,2], Opt_LlvmTBAA)
 
 --     , ([2],     Opt_StaticArgumentTransformation)
 -- Max writes: I think it's probably best not to enable SAT with -O2 for the

docs/users_guide/flags.xml

@@ -1545,6 +1545,15 @@
 	      <entry><option>-fno-liberate-case-threshold</option></entry>
 	    </row>
 
+	    <row>
+	      <entry><option>-fllvm-tbaa</replaceable></entry>
+	      <entry>Turn on Typed Based Alias Analysis information in the LLVM
+	        backend. This enables more accurate and alias information in the LLVM
+	        backend for better optimisation. (default: Enabled)</entry>
+	      <entry>dynamic</entry>
+	      <entry><option>-fno-llvm-tbaa</option></entry>
+	    </row>
+
 	    <row>
 	      <entry><option>-fmax-simplifier-iterations</option></entry>
 	      <entry>Set the max iterations for the simplifier</entry>