From 2fe8f2cd7441a7c8be4ef112453a5b7ed8388e02 Mon Sep 17 00:00:00 2001
From: Frits van Bommel <fvbommel@wxs.nl>
Date: Sun, 31 May 2009 12:43:59 +0200
Subject: [PATCH] Improve ABI conformance on x86 by passing the `sret`
 parameter in EAX if there's no `this`.

---
 gen/abi.cpp    | 10 +++++++++-
 gen/tocall.cpp |  3 ++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/gen/abi.cpp b/gen/abi.cpp
index 4551c1ce..130e49f1 100644
--- a/gen/abi.cpp
+++ b/gen/abi.cpp
@@ -196,8 +196,16 @@ struct X86TargetABI : TargetABI
                 Logger::println("Putting context ptr in register");
                 fty.arg_nest->attrs = llvm::Attribute::InReg;
             }
+            else if (IrFuncTyArg* sret = fty.arg_sret)
+            {
+                Logger::println("Putting sret ptr in register");
+                // sret and inreg are incompatible, but the ABI requires the
+                // sret parameter to be in EAX in this situation...
+                sret->attrs = (sret->attrs | llvm::Attribute::InReg)
+                                & ~llvm::Attribute::StructRet;
+            }
             // otherwise try to mark the last param inreg
-            else if (!fty.arg_sret && !fty.args.empty())
+            else if (!fty.args.empty())
             {
                 // The last parameter is passed in EAX rather than being pushed on the stack if the following conditions are met:
                 //   * It fits in EAX.
diff --git a/gen/tocall.cpp b/gen/tocall.cpp
index fea5e91a..62b373d8 100644
--- a/gen/tocall.cpp
+++ b/gen/tocall.cpp
@@ -322,7 +322,8 @@ DValue* DtoCallFunction(Loc& loc, Type* resulttype, DValue* fnval, Expressions*
         // add attrs for hidden ptr
         Attr.Index = 1;
         Attr.Attrs = tf->fty.arg_sret->attrs;
-        assert((Attr.Attrs & llvm::Attribute::StructRet) && "Sret arg not sret?");
+        assert((Attr.Attrs & (llvm::Attribute::StructRet | llvm::Attribute::InReg))
+            && "Sret arg not sret or inreg?");
         attrs.push_back(Attr);
     }