Improved pattern compilation

src/fsharp/CompilerImports.fs

@@ -1830,12 +1830,12 @@ and [<Sealed>] TcImports(tcConfigP: TcConfigProvider, initialResolutions: TcAsse
         let primaryScopeRef =
             match primaryAssem with
               | _, [ResolvedImportedAssembly ccu] -> ccu.FSharpViewOfMetadata.ILScopeRef
-              | _ -> failwith "unexpected"
+              | _ -> failwith "primaryScopeRef - unexpected"
 
         let primaryAssemblyResolvedPath =
             match primaryAssemblyResolution with
             | [primaryAssemblyResolution] -> primaryAssemblyResolution.resolvedPath
-            | _ -> failwith "unexpected"
+            | _ -> failwith "primaryAssemblyResolvedPath - unexpected"
 
         let resolvedAssemblies = tcResolutions.GetAssemblyResolutions()
 

src/fsharp/IlxGen.fs

@@ -3815,6 +3815,7 @@ and eligibleForFilter (cenv: cenv) expr =
        | Expr.Op(TOp.Coerce _, _, _, _) -> true
        | Expr.Val _ -> true
        | _ -> false
+
    and checkDecisionTree dtree =
        match dtree with
        | TDSwitch(ve, cases, dflt, _) -> 
@@ -3823,6 +3824,7 @@ and eligibleForFilter (cenv: cenv) expr =
            dflt |> Option.forall checkDecisionTree 
        | TDSuccess (es, _) -> es |> List.forall check
        | TDBind(bind, rest) -> check bind.Expr && checkDecisionTree rest
+
    and checkDecisionTreeCase dcase =
        let (TCase(test, tree)) = dcase
        checkDecisionTree tree &&
@@ -4162,6 +4164,11 @@ and GenAsmCode cenv cgbuf eenv (il, tyargs, args, returnTys, m) sequel =
               GenSequel cenv eenv.cloc cgbuf sequel
           | _ -> failwith "Bad polymorphic IL instruction"
 
+    // ldnull; cgt.un then branch is used to test for null and can become a direct brtrue/brfalse
+    | [ AI_ldnull; AI_cgt_un ], [arg1], CmpThenBrOrContinue(1, [ I_brcmp (bi, label1) ]), _ ->
+
+        GenExpr cenv cgbuf eenv arg1 (CmpThenBrOrContinue(pop 1, [ I_brcmp (bi, label1) ]))
+
     // Strip off any ("ceq" x false) when the sequel is a comparison branch and change the BI_brfalse to a BI_brtrue
     // This is the instruction sequence for "not"
     // For these we can just generate the argument and change the test (from a brfalse to a brtrue and vice versa)
@@ -4170,19 +4177,21 @@ and GenAsmCode cenv cgbuf eenv (il, tyargs, args, returnTys, m) sequel =
        CmpThenBrOrContinue(1, [I_brcmp (BI_brfalse | BI_brtrue as bi, label1) ]),
        _) ->
 
-            let bi = match bi with BI_brtrue -> BI_brfalse | _ -> BI_brtrue
-            GenExpr cenv cgbuf eenv arg1 (CmpThenBrOrContinue(pop 1, [ I_brcmp (bi, label1) ]))
+        let bi = match bi with BI_brtrue -> BI_brfalse | _ -> BI_brtrue
+        GenExpr cenv cgbuf eenv arg1 (CmpThenBrOrContinue(pop 1, [ I_brcmp (bi, label1) ]))
 
     // Query; when do we get a 'ret' in IL assembly code?
     | [ I_ret ], [arg1], sequel, [_ilRetTy] ->
-          GenExpr cenv cgbuf eenv arg1 Continue
-          CG.EmitInstr cgbuf (pop 1) Push0 I_ret
-          GenSequelEndScopes cgbuf sequel
+
+        GenExpr cenv cgbuf eenv arg1 Continue
+        CG.EmitInstr cgbuf (pop 1) Push0 I_ret
+        GenSequelEndScopes cgbuf sequel
 
     // Query; when do we get a 'ret' in IL assembly code?
     | [ I_ret ], [], sequel, [_ilRetTy] ->
-          CG.EmitInstr cgbuf (pop 1) Push0 I_ret
-          GenSequelEndScopes cgbuf sequel
+
+        CG.EmitInstr cgbuf (pop 1) Push0 I_ret
+        GenSequelEndScopes cgbuf sequel
 
     // 'throw' instructions are a bit of a problem - e.g. let x = (throw ...) in ... expects a value *)
     // to be left on the stack. But dead-code checking by some versions of the .NET verifier *)
@@ -5756,8 +5765,8 @@ and GenDecisionTreeSwitch cenv cgbuf inplabOpt stackAtTargets eenv e cases defau
         match firstDiscrim with
         // Iterated tests, e.g. exception constructors, nulltests, typetests and active patterns.
         // These should always have one positive and one negative branch
-        | DecisionTreeTest.IsInst _
         | DecisionTreeTest.ArrayLength _
+        | DecisionTreeTest.IsInst _
         | DecisionTreeTest.IsNull
         | DecisionTreeTest.Const(Const.Zero) ->
             if not (isSingleton cases) || Option.isNone defaultTargetOpt then failwith "internal error: GenDecisionTreeSwitch: DecisionTreeTest.IsInst/isnull/query"
@@ -5781,7 +5790,9 @@ and GenDecisionTreeSwitch cenv cgbuf inplabOpt stackAtTargets eenv e cases defau
             CG.EmitInstr cgbuf (pop 1) Push0 (I_brcmp (bi, (List.head caseLabels).CodeLabel))
             GenDecisionTreeCases cenv cgbuf stackAtTargets eenv defaultTargetOpt targets targetCounts targetInfos sequel caseLabels cases contf
 
-        | DecisionTreeTest.ActivePatternCase _ -> error(InternalError("internal error in codegen: DecisionTreeTest.ActivePatternCase", switchm))
+        | DecisionTreeTest.ActivePatternCase _ ->
+            error(InternalError("internal error in codegen: DecisionTreeTest.ActivePatternCase", switchm))
+
         | DecisionTreeTest.UnionCase (hdc, tyargs) ->
             GenExpr cenv cgbuf eenv e Continue
             let cuspec = GenUnionSpec cenv.amap m eenv.tyenv hdc.TyconRef tyargs
@@ -5841,7 +5852,8 @@ and GenDecisionTreeSwitch cenv cgbuf inplabOpt stackAtTargets eenv e cases defau
                 GenDecisionTreeCases cenv cgbuf stackAtTargets eenv defaultTargetOpt targets targetCounts targetInfos sequel caseLabels cases contf
             | _ -> error(InternalError("these matches should never be needed", switchm))
 
-        | DecisionTreeTest.Error m -> error(InternalError("Trying to compile error recovery branch", m))
+        | DecisionTreeTest.Error m ->
+            error(InternalError("Trying to compile error recovery branch", m))
 
 and GenDecisionTreeCases cenv cgbuf stackAtTargets eenv defaultTargetOpt targets targetCounts targetInfos sequel caseLabels cases (contf: Zmap<_,_> -> FakeUnit) =
 
@@ -7417,7 +7429,7 @@ and GenModuleDef cenv (cgbuf: CodeGenBuffer) qname lazyInitInfo eenv x =
                 let recBinds =
                     bindsRemaining
                     |> List.takeWhile (function ModuleOrNamespaceBinding.Binding _ -> true | _ -> false)
-                    |> List.map (function ModuleOrNamespaceBinding.Binding recBind -> recBind | _ -> failwith "unexpected")
+                    |> List.map (function ModuleOrNamespaceBinding.Binding recBind -> recBind | _ -> failwith "GenModuleDef - unexpected")
                 let otherBinds =
                     bindsRemaining
                     |> List.skipWhile (function ModuleOrNamespaceBinding.Binding _ -> true | _ -> false) 

src/fsharp/Optimizer.fs

@@ -3695,6 +3695,17 @@ and TryOptimizeDecisionTreeTest cenv test vinfo =
 
 /// Optimize/analyze a switch construct from pattern matching 
 and OptimizeSwitch cenv env (e, cases, dflt, m) =
+    let g = cenv.g
+
+    // Replace IsInst tests by calls to the helper for type tests, which may then get optimized
+    let e, cases =
+        match cases with
+        | [ TCase(DecisionTreeTest.IsInst (_srcTy, tgTy), success)] ->
+            let testExpr = mkCallTypeTest g m tgTy e
+            let testCases = [TCase(DecisionTreeTest.Const(Const.Bool true), success)]
+            testExpr, testCases
+        | _ -> e, cases
+
     let eR, einfo = OptimizeExpr cenv env e 
 
     let cases, dflt = 
@@ -3708,7 +3719,8 @@ and OptimizeSwitch cenv env (e, cases, dflt, m) =
                 dflt
         else
             cases, dflt 
-    // OK, see what weRre left with and continue
+
+    // OK, see what we are left with and continue
     match cases, dflt with 
     | [], Some case -> OptimizeDecisionTree cenv env m case
     | _ -> OptimizeSwitchFallback cenv env (eR, einfo, cases, dflt, m)