[AVR] Add support for the -mdouble=x flag

[aykevl]

Summary

This flag is used by avr-gcc (starting with v10) to set the width of the double type. The double type is by default interpreted as a 32-bit floating point number in avr-gcc instead of a 64-bit floating point number as is common on other architectures. Starting with GCC 10, a new option has been added to control this behavior:
https://gcc.gnu.org/wiki/avr-gcc#Deviations_from_the_Standard

This commit keeps the default double at 32 bits but adds support for the -mdouble flag (-mdouble=32 and -mdouble=64) to control this behavior.

[MaskRay]

The GCC side commits can be found on https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92055
So it seems that we will have both -mlong-double-{64,80,128} (80 is used by x86 fp80) and -mlong-double={32,64}... (I actually prefer = to -)

clang/lib/Driver/ToolChains/Clang.cpp

4594

Nit: move this before the -mlong-double- processing.

clang/test/CodeGen/mdouble.c

2

Maybe name this file avr-mdouble.c

clang/test/Driver/mdouble.c

2

-unknown-unknown can be deleted

[aykevl]

Fixed nits.

[aykevl]

In D76181#1923176, @MaskRay wrote:

The GCC side commits can be found on https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92055
So it seems that we will have both -mlong-double-{64,80,128} (80 is used by x86 fp80) and -mlong-double={32,64}... (I actually prefer = to -)

Yeah I honestly think the -mlong-double-{64,80,128} flags are pretty ugly, they should have been -mlong-double={64,80,128}. Unfortunately I don't think that can be changed anymore.
I briefly considered using the -mdouble-{32,64} format for AVR but apart from it being rather ugly, avr-gcc uses -mdouble={32,64} (with = instead of -). That means there will be two closely related flags in Clang with a different format. I can change it if necessary, although I have a slight preference to match avr-gcc.

clang/test/CodeGen/mdouble.c

2

I named this mdouble.c instead of avr-mdouble.c as it seems to me that this flag may be useful for other targets as well and tests can be added to the same file. I can rename this if you think avr-mdouble.c is more appropriate.

clang/include/clang/Basic/LangOptions.def

 COMPATIBLE_LANGOPT(Optimize          , 1, 0, "__OPTIMIZE__ predefined macro")
 COMPATIBLE_LANGOPT(OptimizeSize      , 1, 0, "__OPTIMIZE_SIZE__ predefined macro")
 COMPATIBLE_LANGOPT(Static            , 1, 0, "__STATIC__ predefined macro (as opposed to __DYNAMIC__)")
 VALUE_LANGOPT(PackStruct  , 32, 0,
               "default struct packing maximum alignment")
 VALUE_LANGOPT(MaxTypeAlign  , 32, 0,
               "default maximum alignment for types")
 VALUE_LANGOPT(AlignDouble            , 1, 0, "Controls if doubles should be aligned to 8 bytes (x86 only)")
+VALUE_LANGOPT(DoubleSize            , 32, 0, "width of double")
 VALUE_LANGOPT(LongDoubleSize        , 32, 0, "width of long double")
 LANGOPT(PPCIEEELongDouble            , 1, 0, "use IEEE 754 quadruple-precision for long double")
 COMPATIBLE_VALUE_LANGOPT(PICLevel    , 2, 0, "__PIC__ level")
 COMPATIBLE_VALUE_LANGOPT(PIE         , 1, 0, "is pie")
 LANGOPT(ROPI                         , 1, 0, "Read-only position independence")
 LANGOPT(RWPI                         , 1, 0, "Read-write position independence")
 COMPATIBLE_LANGOPT(GNUInline         , 1, 0, "GNU inline semantics")
 COMPATIBLE_LANGOPT(NoInlineDefine    , 1, 0, "__NO_INLINE__ predefined macro")

clang/include/clang/Driver/Options.td

 def malign_branch_boundary_EQ : Joined<["-"], "malign-branch-boundary=">, Group<m_Group>, Flags<[DriverOption]>,
   HelpText<"Specify the boundary's size to align branches">;
 def malign_branch_prefix_size_EQ : Joined<["-"], "malign-branch-prefix-size=">, Group<m_Group>;
 def mbranches_within_32B_boundaries : Flag<["-"], "mbranches-within-32B-boundaries">, Flags<[DriverOption]>, Group<m_Group>,
   HelpText<"Align selected branches (fused, jcc, jmp) within 32-byte boundary">;
 def mfancy_math_387 : Flag<["-"], "mfancy-math-387">, Group<clang_ignored_m_Group>;
 def mlong_calls : Flag<["-"], "mlong-calls">, Group<m_Group>,
   HelpText<"Generate branches with extended addressability, usually via indirect jumps.">;
+def mdouble_EQ : Joined<["-"], "mdouble=">, Group<m_Group>, Values<"32,64">, Flags<[CC1Option]>,
+  HelpText<"Force double to be 32 bits or 64 bits">;
 def LongDouble_Group : OptionGroup<"<LongDouble group>">, Group<m_Group>,
   DocName<"Long double flags">,
   DocBrief<[{Selects the long double implementation}]>;
 def mlong_double_64 : Flag<["-"], "mlong-double-64">, Group<LongDouble_Group>, Flags<[CC1Option]>,
   HelpText<"Force long double to be 64 bits">;
 def mlong_double_80 : Flag<["-"], "mlong-double-80">, Group<LongDouble_Group>, Flags<[CC1Option]>,
   HelpText<"Force long double to be 80 bits, padded to 128 bits for storage">;
 def mlong_double_128 : Flag<["-"], "mlong-double-128">, Group<LongDouble_Group>, Flags<[CC1Option]>,

clang/lib/Basic/TargetInfo.cpp

if (Opts.OpenCL) {
     IntMaxType = SignedLongLong;
     Int64Type = SignedLong;
 
     HalfFormat = &llvm::APFloat::IEEEhalf();
     FloatFormat = &llvm::APFloat::IEEEsingle();
     LongDoubleFormat = &llvm::APFloat::IEEEquad();
   }
 
+  if (Opts.DoubleSize) {
+    if (Opts.DoubleSize == 32) {
+      DoubleWidth = 32;
+      LongDoubleWidth = 32;
+      DoubleFormat = &llvm::APFloat::IEEEsingle();
+      LongDoubleFormat = &llvm::APFloat::IEEEsingle();
+    } else if (Opts.DoubleSize == 64) {
+      DoubleWidth = 64;
+      LongDoubleWidth = 64;
+      DoubleFormat = &llvm::APFloat::IEEEdouble();
+      LongDoubleFormat = &llvm::APFloat::IEEEdouble();
+    }
+  }
+
   if (Opts.LongDoubleSize) {
     if (Opts.LongDoubleSize == DoubleWidth) {
       LongDoubleWidth = DoubleWidth;
       LongDoubleAlign = DoubleAlign;
       LongDoubleFormat = DoubleFormat;
     } else if (Opts.LongDoubleSize == 128) {
       LongDoubleWidth = LongDoubleAlign = 128;
       LongDoubleFormat = &llvm::APFloat::IEEEquad();

clang/lib/Driver/ToolChains/Clang.cpp

 
   // Handle segmented stacks.
   if (Args.hasArg(options::OPT_fsplit_stack))
     CmdArgs.push_back("-split-stacks");
 
   RenderFloatingPointOptions(TC, D, OFastEnabled, Args, CmdArgs,
                              JA.getOffloadingDeviceKind());
 
+  if (Arg *A = Args.getLastArg(options::OPT_mdouble_EQ)) {
+    if (TC.getArch() == llvm::Triple::avr)
+      A->render(Args, CmdArgs);
+    else
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getAsString(Args) << TripleStr;
+  }
+
   if (Arg *A = Args.getLastArg(options::OPT_LongDouble_Group)) {
     if (TC.getTriple().isX86())
       A->render(Args, CmdArgs);
     else if ((TC.getArch() == llvm::Triple::ppc || TC.getTriple().isPPC64()) &&
              (A->getOption().getID() != options::OPT_mlong_double_80))
       A->render(Args, CmdArgs);
     else
       D.Diag(diag::err_drv_unsupported_opt_for_target)
           << A->getAsString(Args) << TripleStr;
   }
 
   // Decide whether to use verbose asm. Verbose assembly is the default on

clang/lib/Frontend/CompilerInvocation.cpp

   Opts.ObjCDefaultSynthProperties =
     !Args.hasArg(OPT_disable_objc_default_synthesize_properties);
   Opts.EncodeExtendedBlockSig =
     Args.hasArg(OPT_fencode_extended_block_signature);
   Opts.EmitAllDecls = Args.hasArg(OPT_femit_all_decls);
   Opts.PackStruct = getLastArgIntValue(Args, OPT_fpack_struct_EQ, 0, Diags);
   Opts.MaxTypeAlign = getLastArgIntValue(Args, OPT_fmax_type_align_EQ, 0, Diags);
   Opts.AlignDouble = Args.hasArg(OPT_malign_double);
+  Opts.DoubleSize = getLastArgIntValue(Args, OPT_mdouble_EQ, 0, Diags);
   Opts.LongDoubleSize = Args.hasArg(OPT_mlong_double_128)
                             ? 128
                             : Args.hasArg(OPT_mlong_double_64) ? 64 : 0;
   Opts.PPCIEEELongDouble = Args.hasArg(OPT_mabi_EQ_ieeelongdouble);
   Opts.PICLevel = getLastArgIntValue(Args, OPT_pic_level, 0, Diags);
   Opts.ROPI = Args.hasArg(OPT_fropi);
   Opts.RWPI = Args.hasArg(OPT_frwpi);
   Opts.PIE = Args.hasArg(OPT_pic_is_pie);

clang/test/CodeGen/mdouble.c

+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=avr-unknown-unknown -mdouble=64 | \
+// RUN:   FileCheck --check-prefix=AVR-FP64 %s
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=avr-unknown-unknown -mdouble=32 | \
+// RUN:   FileCheck --check-prefix=AVR-FP32 %s
+
+double x = 0;
+int size = sizeof(x);
+
+// FIXME: the double should have an alignment of 1 on AVR, not 4 or 8.
+// AVR-FP64: @x = global double {{.*}}, align 8
+// AVR-FP64: @size = global i16 8
+// AVR-FP32: @x = global float {{.*}}, align 4
+// AVR-FP32: @size = global i16 4

clang/test/Driver/mdouble.c

+// RUN: %clang -target avr -c -### %s -mdouble=64 2>&1 | FileCheck %s
+
+// CHECK: "-mdouble=64"
+
+// RUN: %clang -target aarch64 -c -### %s -mdouble=64 2>&1 | FileCheck --check-prefix=ERR %s
+
+// ERR: error: unsupported option '-mdouble=64' for target 'aarch64'