llvmGen: Fix #14251

Fixes the calling convention for functions passing raw SSE-register
values by adding padding as needed to get the values in the right
registers. This problem cropped up when some args were unused an dropped
from the live list.

This folds together 2e23e1c7de01c92b038e55ce53d11bf9db993dd4 and
73273be476a8cc6c13368660b042b3b0614fd928 previously from @kavon.

Metric Increase:
    T12707
    ManyConstructors

1 files changed, 10 insertions, 12 deletions

diff --git a/compiler/llvmGen/LlvmCodeGen/CodeGen.hs b/compiler/llvmGen/LlvmCodeGen/CodeGen.hs
index 7a6e3386ae..bfaf7706d1 100644
--- a/compiler/llvmGen/LlvmCodeGen/CodeGen.hs
+++ b/compiler/llvmGen/LlvmCodeGen/CodeGen.hs
@@ -1841,19 +1841,14 @@ funPrologue live cmmBlocks = do
 -- STG Liveness optimisation done here.
 funEpilogue :: LiveGlobalRegs -> LlvmM ([LlvmVar], LlvmStatements)
 funEpilogue live = do
+    dflags <- getDynFlags
 
-    -- Have information and liveness optimisation is enabled?
-    let liveRegs = alwaysLive ++ live
-        isSSE (FloatReg _)  = True
-        isSSE (DoubleReg _) = True
-        isSSE (XmmReg _)    = True
-        isSSE (YmmReg _)    = True
-        isSSE (ZmmReg _)    = True
-        isSSE _             = False
+    -- the bool indicates whether the register is padding.
+    let alwaysNeeded = map (\r -> (False, r)) alwaysLive
+        livePadded = alwaysNeeded ++ padLiveArgs dflags live
 
     -- Set to value or "undef" depending on whether the register is
     -- actually live
-    dflags <- getDynFlags
     let loadExpr r = do
           (v, _, s) <- getCmmRegVal (CmmGlobal r)
           return (Just $ v, s)
@@ -1861,9 +1856,12 @@ funEpilogue live = do
           let ty = (pLower . getVarType $ lmGlobalRegVar dflags r)
           return (Just $ LMLitVar $ LMUndefLit ty, nilOL)
     platform <- getDynFlag targetPlatform
-    loads <- flip mapM (activeStgRegs platform) $ \r -> case () of
-      _ | r `elem` liveRegs  -> loadExpr r
-        | not (isSSE r)      -> loadUndef r
+    let allRegs = activeStgRegs platform
+    loads <- flip mapM allRegs $ \r -> case () of
+      _ | (False, r) `elem` livePadded
+                             -> loadExpr r   -- if r is not padding, load it
+        | not (isFPR r) || (True, r) `elem` livePadded
+                             -> loadUndef r
         | otherwise          -> return (Nothing, nilOL)
 
     let (vars, stmts) = unzip loads