emit better code for try-finally when function does not throw

src/ddmd/backend/cc.d

@@ -408,8 +408,8 @@ enum
     BFLnostackopt    = 8,       // set when stack elimination should not
                                 // be done
     // NTEXCEPTIONS
-    BFLehcode        = 0x10,    // set when we need to load exception code
-    BFLunwind        = 0x1000,  // do local_unwind following block
+    BFLehcode        = 0x10,    // BC_filter: need to load exception code
+    BFLunwind        = 0x1000,  // do local_unwind following block (unused)
 
     BFLnomerg        = 0x20,    // do not merge with other blocks
     BFLprolog        = 0x80,    // generate function prolog
@@ -668,6 +668,7 @@ enum
     Fnotailrecursion = 0x4000,  // no tail recursion optimizations
     Ffakeeh          = 0x8000,  // allocate space for NT EH context sym anyway
     Fnothrow         = 0x10000, // function does not throw (even if not marked 'nothrow')
+    Feh_none         = 0x20000, // ehmethod==EH_NONE for this function only
 }
 
 struct func_t

src/ddmd/backend/cc.h

@@ -418,8 +418,8 @@ enum
     BFLnostackopt    = 8,       // set when stack elimination should not
                                 // be done
 #if NTEXCEPTIONS
-    BFLehcode        = 0x10,    // set when we need to load exception code
-    BFLunwind        = 0x1000,  // do local_unwind following block
+    BFLehcode        = 0x10,    // BC_filter: need to load exception code
+    BFLunwind        = 0x1000,  // do local_unwind following block (unused)
 #endif
     BFLnomerg        = 0x20,    // do not merge with other blocks
     BFLprolog        = 0x80,    // generate function prolog
@@ -709,6 +709,7 @@ enum
     Fnotailrecursion = 0x4000,  // no tail recursion optimizations
     Ffakeeh          = 0x8000,  // allocate space for NT EH context sym anyway
     Fnothrow         = 0x10000, // function does not throw (even if not marked 'nothrow')
+    Feh_none         = 0x20000, // ehmethod==EH_NONE for this function only
 };
 
 struct func_t
@@ -1412,6 +1413,18 @@ struct Aliassym : Symbol { };
     inline char *prettyident(Symbol *s) { return s->Sident; }
 #endif
 
+/************************
+ * Params:
+ *      f = function symbol
+ * Returns:
+ *      exception method for f
+ */
+inline EHmethod ehmethod(Symbol *f)
+{
+    return f->Sfunc->Fflags3 & Feh_none ? EH_NONE : config.ehmethod;
+}
+
+
 
 /**********************************
  * Function parameters:

src/ddmd/backend/cod3.c

@@ -7,6 +7,7 @@
  * Authors:     $(LINK2 http://www.digitalmars.com, Walter Bright)
  * License:     $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
  * Source:      $(LINK2 https://github.com/dlang/dmd/blob/master/src/ddmd/backend/cod3.c, backend/cod3.c)
+ * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/ddmd/backend/cod3.c
  */
 
 #if !SPP
@@ -825,7 +826,8 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
             break;
         }
 #if MARS
-        case BCjcatch:
+        case BCjcatch:          // D catch clause of try-catch
+            assert(ehmethod(funcsym_p) != EH_NONE);
             // Mark all registers as destroyed. This will prevent
             // register assignments to variables used in catch blocks.
             getregs(cdb,lpadregs());
@@ -843,7 +845,7 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
             goto case_goto;
 #endif
 #if SCPP
-        case BCcatch:
+        case BCcatch:           // C++ catch clause of try-catch
             // Mark all registers as destroyed. This will prevent
             // register assignments to variables used in catch blocks.
             getregs(cdb,allregs | mES);
@@ -859,7 +861,7 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
             nextb = bl->nthSucc(0);
             if ((MARS ||
                  funcsym_p->Sfunc->Fflags3 & Fnteh) &&
-                config.ehmethod != EH_DWARF &&
+                ehmethod(funcsym_p) != EH_DWARF &&
                 bl->Btry != nextb->Btry &&
                 nextb->BC != BC_finally)
             {
@@ -878,7 +880,8 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
                     }
                 }
 #endif
-                if (config.ehmethod == EH_WIN32 || config.ehmethod == EH_SEH)
+                if (config.ehmethod == EH_WIN32 && !(funcsym_p->Sfunc->Fflags3 & Feh_none) ||
+                    config.ehmethod == EH_SEH)
                 {
                     nteh_unwind(cdb,0,toindex);
                 }
@@ -941,8 +944,12 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
         }
 
         case BC_try:
-            if (config.ehmethod == EH_NONE)
+            if (config.ehmethod == EH_NONE || funcsym_p->Sfunc->Fflags3 & Feh_none)
             {
+                /* Need to use frame pointer to access locals, not the stack pointer,
+                 * because we'll be calling the BC_finally blocks and the stack will be off.
+                 */
+                usednteh |= EHtry;
             }
             else if (config.ehmethod == EH_SEH || config.ehmethod == EH_WIN32)
             {
@@ -954,7 +961,7 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
             goto case_goto;
 
         case BC_finally:
-            if (config.ehmethod == EH_DWARF)
+            if (ehmethod(funcsym_p) == EH_DWARF)
             {
                 // Mark scratch registers as destroyed.
                 getregsNoSave(lpadregs());
@@ -969,7 +976,8 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
             }
             else
             {
-                if (config.ehmethod == EH_SEH || config.ehmethod == EH_WIN32)
+                if (config.ehmethod == EH_SEH ||
+                    config.ehmethod == EH_WIN32 && !(funcsym_p->Sfunc->Fflags3 & Feh_none))
                 {
                     // Mark all registers as destroyed. This will prevent
                     // register assignments to variables used in finally blocks.
@@ -988,7 +996,7 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
 
         case BC_lpad:
         {
-            assert(config.ehmethod == EH_DWARF);
+            assert(ehmethod(funcsym_p) == EH_DWARF);
             // Mark all registers as destroyed. This will prevent
             // register assignments to variables used in finally blocks.
             getregsNoSave(lpadregs());
@@ -1005,7 +1013,7 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
         {
             regm_t retregs = 0;
             gencodelem(cdb,e,&retregs,TRUE);
-            if (config.ehmethod == EH_DWARF)
+            if (ehmethod(funcsym_p) == EH_DWARF)
             {
             }
             else
@@ -1102,7 +1110,8 @@ void outblkexitcode(CodeBuilder& cdb, block *bl, int& anyspill, const char* sfls
                         continue;
                     }
 #endif
-                    if (config.ehmethod == EH_WIN32 || config.ehmethod == EH_SEH)
+                    if (config.ehmethod == EH_WIN32 && !(funcsym_p->Sfunc->Fflags3 & Feh_none) ||
+                        config.ehmethod == EH_SEH)
                     {
                         if (bt->Bscope_index == 0)
                         {
@@ -2979,6 +2988,7 @@ void prolog_16bit_windows_farfunc(CodeBuilder& cdb, tym_t* tyf, bool* pushds)
 
 void prolog_frame(CodeBuilder& cdb, unsigned farfunc, unsigned* xlocalsize, bool* enter, int* cfa_offset)
 {
+    //printf("prolog_frame\n");
     *cfa_offset = 0;
 
     if (0 && config.exe == EX_WIN64)
@@ -3000,7 +3010,7 @@ void prolog_frame(CodeBuilder& cdb, unsigned farfunc, unsigned* xlocalsize, bool
         (*xlocalsize >= 0x1000 && config.exe & EX_flat) ||
         localsize >= 0x10000 ||
 #if NTEXCEPTIONS == 2
-        (usednteh & ~NTEHjmonitor && (config.ehmethod == EH_WIN32 || config.ehmethod == EH_SEH)) ||
+        (usednteh & ~NTEHjmonitor && (config.ehmethod == EH_WIN32 && !(funcsym_p->Sfunc->Fflags3 & Feh_none) || config.ehmethod == EH_SEH)) ||
 #endif
         (config.target_cpu >= TARGET_80386 &&
          config.flags4 & CFG4speed)
@@ -3014,7 +3024,7 @@ void prolog_frame(CodeBuilder& cdb, unsigned farfunc, unsigned* xlocalsize, bool
             // Don't reorder instructions, as dwarf CFA relies on it
             code_orflag(cdb.last(), CFvolatile);
 #if NTEXCEPTIONS == 2
-        if (usednteh & ~NTEHjmonitor && (config.ehmethod == EH_WIN32 || config.ehmethod == EH_SEH))
+        if (usednteh & ~NTEHjmonitor && (config.ehmethod == EH_WIN32 && !(funcsym_p->Sfunc->Fflags3 & Feh_none) || config.ehmethod == EH_SEH))
         {
             nteh_prolog(cdb);
             int sz = nteh_contextsym_size();
@@ -3365,7 +3375,7 @@ void prolog_trace(CodeBuilder& cdb, bool farfunc, unsigned* regsaved)
     char name[IDMAX+IDOHD+1];
     size_t len = objmod->mangle(funcsym_p,name);
     assert(len < sizeof(name));
-    cdb.genasm((unsigned char *)name,len);             // append func name
+    cdb.genasm((char *)name,len);             // append func name
 #endif
     *regsaved = s->Sregsaved;
 }

src/ddmd/backend/dwarf.c

@@ -6,6 +6,7 @@
  * Authors:     $(LINK2 http://www.digitalmars.com, Walter Bright)
  * License:     $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
  * Source:      $(LINK2 https://github.com/dlang/dmd/blob/master/src/ddmd/backend/dwarf.c, backend/dwarf.c)
+ * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/ddmd/backend/dwarf.c
  */
 
 // Emit Dwarf symbolic debug info
@@ -92,6 +93,11 @@ static char __file__[] = __FILE__;      // for tassert.h
  */
 bool doUnwindEhFrame()
 {
+    if (funcsym_p->Sfunc->Fflags3 & Feh_none)
+    {
+        return (config.exe & (EX_FREEBSD | EX_FREEBSD64)) != 0;
+    }
+
     /* FreeBSD fails when having some frames as having unwinding info and some not.
      * (It hangs in unittests for std.datetime.)
      * g++ on FreeBSD does not generate mixed frames, while g++ on OSX and Linux does.
@@ -1530,7 +1536,7 @@ void dwarf_func_term(Symbol *sfunc)
 
     unsigned funcabbrevcode;
 
-    if (config.ehmethod == EH_DM)
+    if (ehmethod(sfunc) == EH_DM)
     {
         IDXSEC dfseg = dwarf_getsegment(debug_frame_name, 1);
         writeDebugFrameFDE(dfseg, sfunc);

src/ddmd/backend/nteh.c

@@ -541,7 +541,7 @@ code *nteh_patchindex(code* c, int sindex)
 
 void nteh_gensindex(CodeBuilder& cdb, int sindex)
 {
-    if (!(config.ehmethod == EH_WIN32 || config.ehmethod == EH_SEH))
+    if (!(config.ehmethod == EH_WIN32 || config.ehmethod == EH_SEH) || funcsym_p->Sfunc->Fflags3 & Feh_none)
         return;
     // Generate:
     //  MOV     -4[EBP],sindex

src/ddmd/declaration.h

@@ -481,6 +481,7 @@ void builtin_init();
 #define FUNCFLAGreturnInprocess 0x10    // working on inferring 'return' for parameters
 #define FUNCFLAGinlineScanned   0x20    // function has been scanned for inline possibilities
 #define FUNCFLAGinferScope      0x40    // infer 'scope' for parameters
+#define FUNCFLAGhasCatches      0x80    // function has try-catch statements
 
 class FuncDeclaration : public Declaration
 {
@@ -523,6 +524,8 @@ class FuncDeclaration : public Declaration
     CompiledCtfeFunction *ctfeCode;     // Compiled code for interpreter
     int inlineNest;                     // !=0 if nested inline
     bool isArrayOp;                     // true if array operation
+    bool eh_none;                       /// true if no exception unwinding is needed
+
     // true if errors in semantic3 this function's frame ptr
     bool semantic3Errors;
     ForeachStatement *fes;              // if foreach body, this is the foreach

src/ddmd/dsymbolsem.d

@@ -120,7 +120,7 @@ extern(C++) final class Semantic2Visitor : Visitor
 
     override void visit(StaticAssert sa)
     {
-        //printf("StaticAssert::semantic2() %s\n", toChars());
+        //printf("StaticAssert::semantic2() %s\n", sa.toChars());
         auto sds = new ScopeDsymbol();
         sc = sc.push(sds);
         sc.tinst = null;
@@ -1197,6 +1197,15 @@ extern(C++) final class Semantic3Visitor : Visitor
                 if (f.isnothrow && blockexit & BE.throw_)
                     error(funcdecl.loc, "nothrow %s `%s` may throw", funcdecl.kind(), funcdecl.toPrettyChars());
 
+                if (!(blockexit & BE.throw_ || funcdecl.flags & FUNCFLAG.hasCatches))
+                {
+                    /* Disable optimization on Win32 due to
+                     * https://issues.dlang.org/show_bug.cgi?id=17997
+                     */
+                    if (!global.params.isWindows || global.params.is64bit)
+                        funcdecl.eh_none = true;         // don't generate unwind tables for this function
+                }
+
                 if (funcdecl.flags & FUNCFLAG.nothrowInprocess)
                 {
                     if (funcdecl.type == f)
@@ -1368,6 +1377,8 @@ extern(C++) final class Semantic3Visitor : Visitor
                 freq = freq.statementSemantic(sc2);
                 freq.blockExit(funcdecl, false);
 
+                funcdecl.eh_none = false;
+
                 sc2 = sc2.pop();
 
                 if (!global.params.useIn)
@@ -1392,6 +1403,8 @@ extern(C++) final class Semantic3Visitor : Visitor
                 fens = fens.statementSemantic(sc2);
                 fens.blockExit(funcdecl, false);
 
+                funcdecl.eh_none = false;
+
                 sc2 = sc2.pop();
 
                 if (!global.params.useOut)
@@ -1501,7 +1514,9 @@ extern(C++) final class Semantic3Visitor : Visitor
                             s = s.statementSemantic(sc2);
 
                             bool isnothrow = f.isnothrow & !(funcdecl.flags & FUNCFLAG.nothrowInprocess);
-                            int blockexit = s.blockExit(funcdecl, isnothrow);
+                            const blockexit = s.blockExit(funcdecl, isnothrow);
+                            if (blockexit & BE.throw_)
+                                funcdecl.eh_none = false;
                             if (f.isnothrow && isnothrow && blockexit & BE.throw_)
                                 error(funcdecl.loc, "nothrow %s `%s` may throw", funcdecl.kind(), funcdecl.toPrettyChars());
                             if (funcdecl.flags & FUNCFLAG.nothrowInprocess && blockexit & BE.throw_)

src/ddmd/eh.d

@@ -45,14 +45,14 @@ private @property @nogc nothrow auto NPTRSIZE() { return _tysize[TYnptr]; }
 Symbol *except_gentables()
 {
     //printf("except_gentables()\n");
-    if (config.ehmethod == EHmethod.EH_DM)
+    if (config.ehmethod == EHmethod.EH_DM && !(funcsym_p.Sfunc.Fflags3 & Feh_none))
     {
         // BUG: alloca() changes the stack size, which is not reflected
         // in the fixed eh tables.
         if (Alloca.size)
             error(null, 0, 0, "cannot mix core.std.stdlib.alloca() and exception handling in %s()", &funcsym_p.Sident[0]);
 
-        char[13+5+1] name;
+        char[13+5+1] name = void;
         __gshared int tmpnum;
         sprintf(name.ptr,"_HandlerTable%d",tmpnum++);
 

src/ddmd/func.d

@@ -1,4 +1,4 @@
-/**
+/***
  * Compiler implementation of the
  * $(LINK2 http://www.dlang.org, D programming language).
  *
@@ -136,6 +136,7 @@ public:
             catches.push(ctch);
 
             Statement s2 = new TryCatchStatement(Loc(), s._body, catches);
+            fd.eh_none = false;
             replaceCurrent(s2);
             s2.accept(this);
         }
@@ -153,6 +154,7 @@ enum FUNCFLAG : uint
     returnInprocess  = 0x10,   /// working on inferring 'return' for parameters
     inlineScanned    = 0x20,   /// function has been scanned for inline possibilities
     inferScope       = 0x40,   /// infer 'scope' for parameters
+    hasCatches       = 0x80,   /// function has try-catch statements
 }
 
 /***********************************************************
@@ -198,6 +200,7 @@ extern (C++) class FuncDeclaration : Declaration
     CompiledCtfeFunction* ctfeCode;     /// Compiled code for interpreter (not actually)
     int inlineNest;                     /// !=0 if nested inline
     bool isArrayOp;                     /// true if array operation
+    bool eh_none;                       /// true if no exception unwinding is needed
 
     bool semantic3Errors;               /// true if errors in semantic3 this function's frame ptr
     ForeachStatement fes;               /// if foreach body, this is the foreach

src/ddmd/glue.d

@@ -827,6 +827,10 @@ void FuncDeclaration_toObjFile(FuncDeclaration fd, bool multiobj)
     if (fd.isVirtual() && (fd.fensure || fd.frequire))
         f.Fflags3 |= Ffakeeh;
 
+    if (fd.eh_none)
+        // Same as config.ehmethod==EH_NONE, but only for this function
+        f.Fflags3 |= Feh_none;
+
     s.Sclass = global.params.isOSX ? SCcomdat : SCglobal;
     for (Dsymbol p = fd.parent; p; p = p.parent)
     {
@@ -1246,7 +1250,8 @@ void FuncDeclaration_toObjFile(FuncDeclaration fd, bool multiobj)
                 }
             }
         }
-        insertFinallyBlockCalls(f.Fstartblock);
+        if (!(f.Fflags3 & Feh_none))
+            insertFinallyBlockCalls(f.Fstartblock);
     }
 
     // If static constructor

src/ddmd/irstate.d

@@ -258,6 +258,8 @@ struct IRState
          * the best we can do.
          * Nothrow needs to be tracked at the Statement level.
          */
-        return !global.params.useExceptions;
+        FuncDeclaration fd;
+        return !global.params.useExceptions ||
+                (fd = getFunc()) !is null && fd.eh_none;
     }
 }