From 4915e566cb661aa934e133c7c9b21c0d1964490a Mon Sep 17 00:00:00 2001
From: Ian Lynagh <igloo@earth.li>
Date: Sun, 1 May 2011 16:19:06 +0100
Subject: [PATCH] Ignore requests to use backends that aren't available; fixes
 #5145

Now if you try to use "-fasm" with an unreg compiler, for example,
you just get a warning saying it's being ignored.
---
 compiler/main/CodeOutput.lhs |    3 +--
 compiler/main/DynFlags.hs    |   25 +++++++++++++++++++++----
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/compiler/main/CodeOutput.lhs b/compiler/main/CodeOutput.lhs
index 7cfc2e9..f5e3394 100644
--- a/compiler/main/CodeOutput.lhs
+++ b/compiler/main/CodeOutput.lhs
@@ -156,8 +156,7 @@ outputAsm dflags filenm flat_absC
                  nativeCodeGen dflags f ncg_uniqs flat_absC
 
  | otherwise
-  = pprPanic "This compiler was built without a native code generator"
-             (text "Use -fvia-C instead")
+  = panic "This compiler was built without a native code generator"
 \end{code}
 
 
diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index c7e0465..7e15aa4 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -2039,11 +2039,28 @@ setTarget l = upd set
 -- not from bytecode to object-code.  The idea is that -fasm/-fllvm
 -- can be safely used in an OPTIONS_GHC pragma.
 setObjTarget :: HscTarget -> DynP ()
-setObjTarget l = upd set
+setObjTarget l = updM set
   where
-   set dfs
-     | isObjectTarget (hscTarget dfs) = dfs { hscTarget = l }
-     | otherwise = dfs
+   set dflags
+     | isObjectTarget (hscTarget dflags)
+       = case l of
+         HscC
+          | cGhcUnregisterised /= "YES" ->
+             do addWarn ("Compiler not unregisterised, so ignoring " ++
+                         showHscTargetFlag l)
+                return dflags
+         HscAsm
+          | cGhcWithNativeCodeGen /= "YES" ->
+             do addWarn ("Compiler has no native codegen, so ignoring " ++
+                         showHscTargetFlag l)
+                return dflags
+         HscLlvm
+          | cGhcUnregisterised == "YES" ->
+             do addWarn ("Compiler unregisterised, so ignoring " ++
+                         showHscTargetFlag l)
+                return dflags
+         _ -> return $ dflags { hscTarget = l }
+     | otherwise = return dflags
 
 setOptLevel :: Int -> DynFlags -> DynP DynFlags
 setOptLevel n dflags
-- 
1.7.10.4