[CodeGen] Use __extendhfsf2 and __truncsfhf2 by default (#126880)

The standard libcalls for half to float and float to half conversion are
__extendhfsf2 and __truncsfhf2. However, LLVM currently uses
__gnu_h2f_ieee and __gnu_f2h_ieee instead. As far as I can tell, these
libcalls are an ARM-ism and only provided by libgcc on that platform.
compiler-rt always provides both libcalls.

Use the standard libcalls by default, and only use the __gnu libcalls on
ARM.

Author: nikic

lld/test/wasm/lto/Inputs/libcall-return-addr.ll

@@ -0,0 +1,6 @@
+target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-i128:128-f128:64-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-emscripten"
+
+define ptr @emscripten_return_address() {
+  ret ptr null
+}

lld/test/wasm/lto/Inputs/libcall-truncsfhf2.ll

@@ -0,0 +1,18 @@
+; RUN: llvm-as %s -o %t.o
+; RUN: llvm-as %p/Inputs/libcall-return-addr.ll -o %t.return-addr.o
+; RUN: rm -f %t.a
+; RUN: llvm-ar rcs %t.a %t.return-addr.o
+; RUN: not wasm-ld --export-all %t.o %t.a -o %t.wasm 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-i128:128-f128:64-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-emscripten"
+
+@g_ptr = global ptr null
+
+define void @_start() {
+  %addr = call ptr @llvm.returnaddress(i32 1)
+  store ptr %addr, ptr @g_ptr
+  ret void
+}
+
+; CHECK: wasm-ld: error: {{.*}}return-addr.o): attempt to add bitcode file after LTO (emscripten_return_address)

lld/test/wasm/lto/libcall-return-addr.ll

@@ -384,8 +384,8 @@ HANDLE_LIBCALL(FPEXT_F16_F128, "__extendhftf2")
 HANDLE_LIBCALL(FPEXT_F16_F80, "__extendhfxf2")
 HANDLE_LIBCALL(FPEXT_F32_F64, "__extendsfdf2")
 HANDLE_LIBCALL(FPEXT_F16_F64, "__extendhfdf2")
-HANDLE_LIBCALL(FPEXT_F16_F32, "__gnu_h2f_ieee")
-HANDLE_LIBCALL(FPROUND_F32_F16, "__gnu_f2h_ieee")
+HANDLE_LIBCALL(FPEXT_F16_F32, "__extendhfsf2")
+HANDLE_LIBCALL(FPROUND_F32_F16, "__truncsfhf2")
 HANDLE_LIBCALL(FPROUND_F64_F16, "__truncdfhf2")
 HANDLE_LIBCALL(FPROUND_F80_F16, "__truncxfhf2")
 HANDLE_LIBCALL(FPROUND_F128_F16, "__trunctfhf2")

lld/test/wasm/lto/libcall-truncsfhf2.ll

@@ -170,9 +170,6 @@ void RuntimeLibcallsInfo::initLibcalls(const Triple &TT) {
     // TODO: BridgeOS should be included in isOSDarwin.
     setLibcallName(RTLIB::EXP10_F32, "__exp10f");
     setLibcallName(RTLIB::EXP10_F64, "__exp10");
-  } else {
-    setLibcallName(RTLIB::FPEXT_F16_F32, "__gnu_h2f_ieee");
-    setLibcallName(RTLIB::FPROUND_F32_F16, "__gnu_f2h_ieee");
   }
 
   if (TT.isGNUEnvironment() || TT.isOSFuchsia() ||

llvm/include/llvm/IR/RuntimeLibcalls.def

@@ -767,6 +767,9 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
       setLibcallName(LC.Op, LC.Name);
       setLibcallCallingConv(LC.Op, LC.CC);
     }
+  } else if (!Subtarget->isTargetMachO()) {
+    setLibcallName(RTLIB::FPROUND_F32_F16, "__gnu_f2h_ieee");
+    setLibcallName(RTLIB::FPEXT_F16_F32, "__gnu_h2f_ieee");
   }
 
   if (Subtarget->isThumb1Only())

llvm/lib/IR/RuntimeLibcalls.cpp

@@ -1886,11 +1886,6 @@ HexagonTargetLowering::HexagonTargetLowering(const TargetMachine &TM,
     setLibcallName(RTLIB::SQRT_F32, "__hexagon_fast2_sqrtf");
   else
     setLibcallName(RTLIB::SQRT_F32, "__hexagon_sqrtf");
-
-  // Routines to handle fp16 storage type.
-  setLibcallName(RTLIB::FPROUND_F32_F16, "__truncsfhf2");
-  setLibcallName(RTLIB::FPROUND_F64_F16, "__truncdfhf2");
-  setLibcallName(RTLIB::FPEXT_F16_F32, "__extendhfsf2");
 }
 
 const char* HexagonTargetLowering::getTargetNodeName(unsigned Opcode) const {

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -1549,9 +1549,6 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   if (Subtarget.useRVVForFixedLengthVectors())
     setTargetDAGCombine(ISD::BITCAST);
 
-  setLibcallName(RTLIB::FPEXT_F16_F32, "__extendhfsf2");
-  setLibcallName(RTLIB::FPROUND_F32_F16, "__truncsfhf2");
-
   // Disable strict node mutation.
   IsStrictFPEnabled = true;
   EnableExtLdPromotion = true;

llvm/lib/Target/Hexagon/HexagonISelLowering.cpp

@@ -377,11 +377,6 @@ WebAssemblyTargetLowering::WebAssemblyTargetLowering(
 
   setMaxAtomicSizeInBitsSupported(64);
 
-  // Override the __gnu_f2h_ieee/__gnu_h2f_ieee names so that the f32 name is
-  // consistent with the f64 and f128 names.
-  setLibcallName(RTLIB::FPEXT_F16_F32, "__extendhfsf2");
-  setLibcallName(RTLIB::FPROUND_F32_F16, "__truncsfhf2");
-
   // Define the emscripten name for return address helper.
   // TODO: when implementing other Wasm backends, make this generic or only do
   // this on emscripten depending on what they end up doing.