Support both Float16 ABIs depending on LLVM and platform (#49527)

There are two Float16 ABIs in the wild, one for platforms that have a
defing register and the original one where we used i16.

LLVM 15 follows GCC and uses the new ABI on x86/ARM but not PPC.

Co-authored-by: Gabriel Baraldi <baraldigabriel@gmail.com>

src/aotcompile.cpp

@@ -494,6 +494,7 @@ static void reportWriterError(const ErrorInfoBase &E)
     jl_safe_printf("ERROR: failed to emit output file %s\n", err.c_str());
 }
 
+#if JULIA_FLOAT16_ABI == 1
 static void injectCRTAlias(Module &M, StringRef name, StringRef alias, FunctionType *FT)
 {
     Function *target = M.getFunction(alias);
@@ -510,7 +511,7 @@ static void injectCRTAlias(Module &M, StringRef name, StringRef alias, FunctionT
     auto val = builder.CreateCall(target, CallArgs);
     builder.CreateRet(val);
 }
-
+#endif
 void multiversioning_preannotate(Module &M);
 
 // See src/processor.h for documentation about this table. Corresponds to jl_image_shard_t.
@@ -943,6 +944,8 @@ struct ShardTimers {
     }
 };
 
+void emitFloat16Wrappers(Module &M, bool external);
+
 // Perform the actual optimization and emission of the output files
 static void add_output_impl(Module &M, TargetMachine &SourceTM, std::string *outputs, const std::string *names,
                     NewArchiveMember *unopt, NewArchiveMember *opt, NewArchiveMember *obj, NewArchiveMember *asm_,
@@ -1003,7 +1006,9 @@ static void add_output_impl(Module &M, TargetMachine &SourceTM, std::string *out
         }
     }
     // no need to inject aliases if we have no functions
+
     if (inject_aliases) {
+#if JULIA_FLOAT16_ABI == 1
         // We would like to emit an alias or an weakref alias to redirect these symbols
         // but LLVM doesn't let us emit a GlobalAlias to a declaration...
         // So for now we inject a definition of these functions that calls our runtime
@@ -1018,8 +1023,10 @@ static void add_output_impl(Module &M, TargetMachine &SourceTM, std::string *out
                 FunctionType::get(Type::getHalfTy(M.getContext()), { Type::getFloatTy(M.getContext()) }, false));
         injectCRTAlias(M, "__truncdfhf2", "julia__truncdfhf2",
                 FunctionType::get(Type::getHalfTy(M.getContext()), { Type::getDoubleTy(M.getContext()) }, false));
+#else
+        emitFloat16Wrappers(M, false);
+#endif
     }
-
     timers.optimize.stopTimer();
 
     if (opt) {

src/codegen.cpp

@@ -5818,6 +5818,7 @@ static void emit_cfunc_invalidate(
         prepare_call_in(gf_thunk->getParent(), jlapplygeneric_func));
 }
 
+#include <iostream>
 static Function* gen_cfun_wrapper(
     Module *into, jl_codegen_params_t &params,
     const function_sig_t &sig, jl_value_t *ff, const char *aliasname,
@@ -8704,6 +8705,58 @@ static JuliaVariable *julia_const_gv(jl_value_t *val)
     return nullptr;
 }
 
+// Handle FLOAT16 ABI v2
+#if JULIA_FLOAT16_ABI == 2
+static void makeCastCall(Module &M, StringRef wrapperName, StringRef calledName, FunctionType *FTwrapper, FunctionType *FTcalled, bool external)
+{
+    Function *calledFun = M.getFunction(calledName);
+    if (!calledFun) {
+        calledFun = Function::Create(FTcalled, Function::ExternalLinkage, calledName, M);
+    }
+    auto linkage = external ? Function::ExternalLinkage : Function::InternalLinkage;
+    auto wrapperFun = Function::Create(FTwrapper, linkage, wrapperName, M);
+    wrapperFun->addFnAttr(Attribute::AlwaysInline);
+    llvm::IRBuilder<> builder(BasicBlock::Create(M.getContext(), "top", wrapperFun));
+    SmallVector<Value *, 4> CallArgs;
+    if (wrapperFun->arg_size() != calledFun->arg_size()){
+        llvm::errs() << "FATAL ERROR: Can't match wrapper to called function";
+        abort();
+    }
+    for (auto wrapperArg = wrapperFun->arg_begin(), calledArg = calledFun->arg_begin();
+            wrapperArg != wrapperFun->arg_end() && calledArg != calledFun->arg_end(); ++wrapperArg, ++calledArg)
+    {
+        CallArgs.push_back(builder.CreateBitCast(wrapperArg, calledArg->getType()));
+    }
+    auto val = builder.CreateCall(calledFun, CallArgs);
+    auto retval = builder.CreateBitCast(val,wrapperFun->getReturnType());
+    builder.CreateRet(retval);
+}
+
+void emitFloat16Wrappers(Module &M, bool external)
+{
+    auto &ctx = M.getContext();
+    makeCastCall(M, "__gnu_h2f_ieee", "julia__gnu_h2f_ieee", FunctionType::get(Type::getFloatTy(ctx), { Type::getHalfTy(ctx) }, false),
+                FunctionType::get(Type::getFloatTy(ctx), { Type::getInt16Ty(ctx) }, false), external);
+    makeCastCall(M, "__extendhfsf2", "julia__gnu_h2f_ieee", FunctionType::get(Type::getFloatTy(ctx), { Type::getHalfTy(ctx) }, false),
+                FunctionType::get(Type::getFloatTy(ctx), { Type::getInt16Ty(ctx) }, false), external);
+    makeCastCall(M, "__gnu_f2h_ieee", "julia__gnu_f2h_ieee", FunctionType::get(Type::getHalfTy(ctx), { Type::getFloatTy(ctx) }, false),
+                FunctionType::get(Type::getInt16Ty(ctx), { Type::getFloatTy(ctx) }, false), external);
+    makeCastCall(M, "__truncsfhf2", "julia__gnu_f2h_ieee", FunctionType::get(Type::getHalfTy(ctx), { Type::getFloatTy(ctx) }, false),
+                FunctionType::get(Type::getInt16Ty(ctx), { Type::getFloatTy(ctx) }, false), external);
+    makeCastCall(M, "__truncdfhf2", "julia__truncdfhf2", FunctionType::get(Type::getHalfTy(ctx), { Type::getDoubleTy(ctx) }, false),
+                FunctionType::get(Type::getInt16Ty(ctx), { Type::getDoubleTy(ctx) }, false), external);
+}
+
+static void init_f16_funcs(void)
+{
+    auto ctx = jl_ExecutionEngine->acquireContext();
+    auto TSM =  jl_create_ts_module("F16Wrappers", ctx, imaging_default());
+    auto aliasM = TSM.getModuleUnlocked();
+    emitFloat16Wrappers(*aliasM, true);
+    jl_ExecutionEngine->addModule(std::move(TSM));
+}
+#endif
+
 static void init_jit_functions(void)
 {
     add_named_global(jlstack_chk_guard_var, &__stack_chk_guard);
@@ -8942,6 +8995,9 @@ extern "C" JL_DLLEXPORT void jl_init_codegen_impl(void)
     jl_init_llvm();
     // Now that the execution engine exists, initialize all modules
     init_jit_functions();
+#if JULIA_FLOAT16_ABI == 2
+    init_f16_funcs();
+#endif
 }
 
 extern "C" JL_DLLEXPORT void jl_teardown_codegen_impl() JL_NOTSAFEPOINT

src/jitlayers.cpp

@@ -1383,6 +1383,7 @@ JuliaOJIT::JuliaOJIT()
 
     JD.addToLinkOrder(GlobalJD, orc::JITDylibLookupFlags::MatchExportedSymbolsOnly);
 
+#if JULIA_FLOAT16_ABI == 1
     orc::SymbolAliasMap jl_crt = {
         { mangle("__gnu_h2f_ieee"), { mangle("julia__gnu_h2f_ieee"), JITSymbolFlags::Exported } },
         { mangle("__extendhfsf2"),  { mangle("julia__gnu_h2f_ieee"), JITSymbolFlags::Exported } },
@@ -1391,6 +1392,7 @@ JuliaOJIT::JuliaOJIT()
         { mangle("__truncdfhf2"),   { mangle("julia__truncdfhf2"),   JITSymbolFlags::Exported } }
     };
     cantFail(GlobalJD.define(orc::symbolAliases(jl_crt)));
+#endif
 
 #ifdef MSAN_EMUTLS_WORKAROUND
     orc::SymbolMap msan_crt;

src/llvm-version.h

@@ -2,6 +2,7 @@
 
 #include <llvm/Config/llvm-config.h>
 #include "julia_assert.h"
+#include "platform.h"
 
 // The LLVM version used, JL_LLVM_VERSION, is represented as a 5-digit integer
 // of the form ABBCC, where A is the major version, B is minor, and C is patch.
@@ -17,6 +18,15 @@
 #define JL_LLVM_OPAQUE_POINTERS 1
 #endif
 
+// Pre GCC 12 libgcc defined the ABI for Float16->Float32
+// to take an i16. GCC 12 silently changed the ABI to now pass
+// Float16 in Float32 registers.
+#if JL_LLVM_VERSION < 150000 || defined(_CPU_PPC64_) || defined(_CPU_PPC_)
+#define JULIA_FLOAT16_ABI 1
+#else
+#define JULIA_FLOAT16_ABI 2
+#endif
+
 #ifdef __cplusplus
 #if defined(__GNUC__) && (__GNUC__ >= 9)
 // Added in GCC 9, this warning is annoying