Don't declare params passed via LLVM byval attribute as DI refs

gen/dibuilder.cpp

@@ -1058,7 +1058,9 @@ void ldc::DIBuilder::EmitLocalVariable(llvm::Value *ll, VarDeclaration *vd,
   // llvm.dbg.declare only works properly with local allocas.
   // Represent variables with non-alloca LL storage as DI references, like `ref`
   // and `out` parameters.
-  const bool storedInAlloca = llvm::dyn_cast<llvm::AllocaInst>(ll);
+  const bool storedInAlloca =
+      llvm::dyn_cast<llvm::AllocaInst>(ll) ||
+      (isaArgument(ll) && isaArgument(ll)->hasByValAttr());
   bool useDbgValueIntrinsic = false;
   if (!storedInAlloca || vd->isRef() || vd->isOut()) {
     // With the exception of special-ref loop variables, the reference/pointer

tests/debuginfo/args_cdb.d

@@ -46,12 +46,13 @@ int byValue(ubyte ub, ushort us, uint ui, ulong ul,
 // CHECK: <function> * fun = {{0x[0-9a-f`]*}}
 // x86: struct int[] slice =
 // CHECK: unsigned char * aa = {{0x[0-9a-f`]*}}
-// CHECK: unsigned char (*)[16] fa
+// x64: unsigned char (*)[16] fa
+// x86: unsigned char [16] fa
 // x86: float [4] f4 = float [4]
 // x86: double [4] d4 = double [4]
-// x64: Small small
-// x86: Small * small
-// CHECK: Large * large
+// CHECK: Small small
+// x64: Large * large
+// x86: Large large
 // CHECK: struct TypeInfo_Class * ti = {{0x[0-9a-f`]*}}
 // CHECK: void * np = {{0x[0`]*}}
 
@@ -80,7 +81,7 @@ int byValue(ubyte ub, ushort us, uint ui, ulong ul,
 
 // CDB: ?? (*fa)[1]
 // x64: unsigned char 0x0e
-// no-x86: unsigned char 0x0e (displays garbage)
+// no-x86: would be fa[1], but displays garbage anyway
 
 // CDB: ?? f4[1]
 // CHECK: float 16
@@ -111,7 +112,7 @@ int byPtr(ubyte* ub, ushort* us, uint* ui, ulong* ul,
           Small* small, Large* large,
           TypeInfo_Class* ti, typeof(null)* np)
 {
-// CDB: bp `args_cdb.d:114`
+// CDB: bp `args_cdb.d:115`
 // CDB: g
     return 3;
 // CHECK: !args_cdb.byPtr
@@ -176,7 +177,7 @@ int byRef(ref ubyte ub, ref ushort us, ref uint ui, ref ulong ul,
           ref Small small, ref Large large,
           ref TypeInfo_Class ti, ref typeof(null) np)
 {
-// CDB: bp `args_cdb.d:179`
+// CDB: bp `args_cdb.d:180`
 // CDB: g
 // CHECK: !args_cdb.byRef