Add BitFieldStyle.Gcc_Clang_ARM

Required for 32-bit ARM, and non-Apple 64-bit ARM targets.

The only difference to `Gcc_Clang` is that anonymous and 0-length
bit-fields do contribute to the aggregate alignment.

Caught by existing proper C interop tests in
runnable_cxx/testbitfields.d on such targets. The hardcoded bad tests
in runnable/{bitfieldsposix64.c,dbitfieldsposix64.d} however now fail
after the fix, on such targets again.

Author: kinke

compiler/src/dmd/dsymbolsem.d

@@ -7186,12 +7186,23 @@ private extern(C++) class SetFieldOffsetVisitor : Visitor
             error(bfd.loc, "bit field width %d is larger than type", bfd.fieldWidth);
 
         const style = target.c.bitFieldStyle;
+        if (style != TargetC.BitFieldStyle.MS &&
+            style != TargetC.BitFieldStyle.Gcc_Clang &&
+            style != TargetC.BitFieldStyle.Gcc_Clang_ARM)
+        {
+            assert(0, "unsupported bit-field style");
+        }
+
+        const isMicrosoftStyle = style == TargetC.BitFieldStyle.MS;
+        const contributesToAggregateAlignment = !anon || style != TargetC.BitFieldStyle.Gcc_Clang;
 
         void startNewField()
         {
             if (log) printf("startNewField()\n");
             uint alignsize;
-            if (style == TargetC.BitFieldStyle.Gcc_Clang)
+            if (isMicrosoftStyle)
+               alignsize = memsize; // not memalignsize
+            else
             {
                 if (bfd.fieldWidth > 32)
                     alignsize = memalignsize;
@@ -7202,15 +7213,13 @@ private extern(C++) class SetFieldOffsetVisitor : Visitor
                 else
                     alignsize = 1;
             }
-            else
-                alignsize = memsize; // not memalignsize
 
             uint dummy;
             bfd.offset = placeField(
                 fieldState.offset,
                 memsize, alignsize, bfd.alignment,
                 ad.structsize,
-                (anon && style == TargetC.BitFieldStyle.Gcc_Clang) ? dummy : ad.alignsize,
+                contributesToAggregateAlignment ? ad.alignsize : dummy,
                 isunion);
 
             fieldState.inFlight = true;
@@ -7219,53 +7228,38 @@ private extern(C++) class SetFieldOffsetVisitor : Visitor
             fieldState.fieldSize = memsize;
         }
 
-        if (style == TargetC.BitFieldStyle.Gcc_Clang)
+        if (ad.alignsize == 0)
+            ad.alignsize = 1;
+        if (!isMicrosoftStyle && contributesToAggregateAlignment && ad.alignsize < memalignsize)
+            ad.alignsize = memalignsize;
+
+        if (bfd.fieldWidth == 0)
         {
-            if (bfd.fieldWidth == 0)
+            if (!isMicrosoftStyle && !isunion)
             {
-                if (!isunion)
-                {
-                    // Use type of zero width field to align to next field
-                    fieldState.offset = (fieldState.offset + memalignsize - 1) & ~(memalignsize - 1);
-                    ad.structsize = fieldState.offset;
-                }
-
-                fieldState.inFlight = false;
-                return;
+                // Use type of zero width field to align to next field
+                fieldState.offset = (fieldState.offset + memalignsize - 1) & ~(memalignsize - 1);
+                ad.structsize = fieldState.offset;
             }
-
-            if (ad.alignsize == 0)
-                ad.alignsize = 1;
-            if (!anon &&
-                  ad.alignsize < memalignsize)
-                ad.alignsize = memalignsize;
-        }
-        else if (style == TargetC.BitFieldStyle.MS)
-        {
-            if (ad.alignsize == 0)
-                ad.alignsize = 1;
-            if (bfd.fieldWidth == 0)
+            else if (isMicrosoftStyle && fieldState.inFlight && !isunion)
             {
-                if (fieldState.inFlight && !isunion)
-                {
-                    // documentation says align to next int
-                    //const alsz = cast(uint)Type.tint32.size();
-                    const alsz = memsize; // but it really does this
-                    fieldState.offset = (fieldState.offset + alsz - 1) & ~(alsz - 1);
-                    ad.structsize = fieldState.offset;
-                }
-
-                fieldState.inFlight = false;
-                return;
+                // documentation says align to next int
+                //const alsz = cast(uint)Type.tint32.size();
+                const alsz = memsize; // but it really does this
+                fieldState.offset = (fieldState.offset + alsz - 1) & ~(alsz - 1);
+                ad.structsize = fieldState.offset;
             }
+
+            fieldState.inFlight = false;
+            return;
         }
 
         if (!fieldState.inFlight)
         {
             //printf("not in flight\n");
             startNewField();
         }
-        else if (style == TargetC.BitFieldStyle.Gcc_Clang)
+        else if (!isMicrosoftStyle)
         {
             // If the bit-field spans more units of alignment than its type,
             // start a new field at the next alignment boundary.
@@ -7288,7 +7282,7 @@ private extern(C++) class SetFieldOffsetVisitor : Visitor
                 }
             }
         }
-        else if (style == TargetC.BitFieldStyle.MS)
+        else
         {
             if (memsize != fieldState.fieldSize ||
                 fieldState.bitOffset + bfd.fieldWidth > fieldState.fieldSize * 8)
@@ -7297,14 +7291,14 @@ private extern(C++) class SetFieldOffsetVisitor : Visitor
                 startNewField();
             }
         }
-        else
-            assert(0);
 
         bfd.offset = fieldState.fieldOffset;
         bfd.bitOffset = fieldState.bitOffset;
 
         const pastField = bfd.bitOffset + bfd.fieldWidth;
-        if (style == TargetC.BitFieldStyle.Gcc_Clang)
+        if (isMicrosoftStyle)
+            fieldState.fieldSize = memsize;
+        else
         {
             auto size = (pastField + 7) / 8;
             fieldState.fieldSize = size;
@@ -7318,8 +7312,6 @@ private extern(C++) class SetFieldOffsetVisitor : Visitor
             else
                 ad.structsize = bfd.offset + size;
         }
-        else
-            fieldState.fieldSize = memsize;
         //printf("at end: ad.structsize = %d\n", cast(int)ad.structsize);
         //print(fieldState);
 

compiler/src/dmd/frontend.h

@@ -5938,6 +5938,7 @@ struct TargetC final
         Unspecified = 0u,
         MS = 1u,
         Gcc_Clang = 2u,
+        Gcc_Clang_ARM = 3u,
     };
 
     bool crtDestructorsSupported;

compiler/src/dmd/target.d

@@ -1379,6 +1379,9 @@ struct TargetC
                               /// https://docs.microsoft.com/en-us/cpp/c-language/c-bit-fields?view=msvc-160
                               /// https://docs.microsoft.com/en-us/cpp/cpp/cpp-bit-fields?view=msvc-160
         Gcc_Clang,            /// gcc and clang
+        Gcc_Clang_ARM,        /// Like `Gcc_Clang`, except that anonymous and 0-length bit fields contribute
+                              /// to the aggregate alignment. Used for 32 & 64 bit ARM targets, except for
+                              /// Apple ARM64.
     }
     bool  crtDestructorsSupported = true; /// Not all platforms support crt_destructor
     ubyte boolsize;           /// size of a C `_Bool` type

compiler/src/dmd/target.h

@@ -65,6 +65,9 @@ struct TargetC
                               // https://docs.microsoft.com/en-us/cpp/c-language/c-bit-fields?view=msvc-160
                               // https://docs.microsoft.com/en-us/cpp/cpp/cpp-bit-fields?view=msvc-160
         Gcc_Clang,            // gcc and clang
+        Gcc_Clang_ARM,        // Like `Gcc_Clang`, except that anonymous and 0-length bit fields contribute
+                              // to the aggregate alignment. Used for 32 & 64 bit ARM targets, except for
+                              // Apple ARM64.
     };
 
     uint8_t crtDestructorsSupported; // Not all platforms support crt_destructor

compiler/src/dmd/todt.d

@@ -958,6 +958,7 @@ private void membersToDt(AggregateDeclaration ad, ref DtBuilder dtb,
             switch (target.c.bitFieldStyle)
             {
                 case TargetC.BitFieldStyle.Gcc_Clang:
+                case TargetC.BitFieldStyle.Gcc_Clang_ARM:
                     bitFieldSize = (bf.bitOffset + bf.fieldWidth + 7) / 8;
                     break;