Fixup stack spills when generating AVX instructions.

LLVM uses aligned AVX moves to spill values onto the stack, which requires
32-bye aligned stacks. Since the stack in only 16-byte aligned, LLVM inserts
extra instructions that munge the stack pointer. This is very very bad for the
GHC calling convention, so we tell LLVM to assume the stack is 32-byte
aligned. This patch rewrites the spill instructions that LLVM generates so they
do not require an aligned stack.

compiler/llvmGen/LlvmMangler.hs

@@ -20,6 +20,10 @@ import System.IO
 import Data.List ( sortBy )
 import Data.Function ( on )
 
+#if x86_64_TARGET_ARCH
+#define REWRITE_AVX
+#endif
+
 -- Magic Strings
 secStmt, infoSec, newLine, textStmt, dataStmt, syntaxUnified :: B.ByteString
 secStmt       = B.pack "\t.section\t"
@@ -47,7 +51,7 @@ llvmFixupAsm dflags f1 f2 = {-# SCC "llvm_mangler" #-} do
     w <- openBinaryFile f2 WriteMode
     ss <- readSections r w
     hClose r
-    let fixed = fixTables ss
+    let fixed = (map rewriteAVX . fixTables) ss
     mapM_ (writeSection w) fixed
     hClose w
     return ()
@@ -90,6 +94,39 @@ writeSection w (hdr, cts) = do
     B.hPutStrLn w hdr
   B.hPutStrLn w cts
 
+#if REWRITE_AVX
+rewriteAVX :: Section -> Section
+rewriteAVX = rewriteVmovaps . rewriteVmovdqa
+
+rewriteVmovdqa :: Section -> Section
+rewriteVmovdqa = rewriteInstructions vmovdqa vmovdqu
+  where
+    vmovdqa, vmovdqu :: B.ByteString
+    vmovdqa = B.pack "vmovdqa"
+    vmovdqu = B.pack "vmovdqu"
+
+rewriteVmovap :: Section -> Section
+rewriteVmovap = rewriteInstructions vmovap vmovup
+  where
+    vmovap, vmovup :: B.ByteString
+    vmovap = B.pack "vmovap"
+    vmovup = B.pack "vmovup"
+
+rewriteInstructions :: B.ByteString -> B.ByteString -> Section -> Section
+rewriteInstructions matchBS replaceBS (hdr, cts) =
+    (hdr, loop cts)
+  where
+    loop :: B.ByteString -> B.ByteString
+    loop cts =
+        case B.breakSubstring cts matchBS of
+          (hd,tl) | B.null tl -> hd
+                  | otherwise -> hd `B.append` replaceBS `B.append`
+                                 loop (B.drop (B.length matchBS) tl)
+#else /* !REWRITE_AVX */
+rewriteAVX :: Section -> Section
+rewriteAVX = id
+#endif /* !REWRITE_SSE */
+
 -- | Reorder and convert sections so info tables end up next to the
 -- code. Also does stack fixups.
 fixTables :: [Section] -> [Section]