[clang] Don't emit IFUNC when targeting Fuchsia

[abrachet]

Summary

Fuchsia's dynamic linker does not and will never support IFUNC's.

[phosek]

LGTM

clang/include/clang/Basic/TargetInfo.h

virtual bool hasFeature(StringRef Feature) const {
     return false;
   }
 
   /// Identify whether this target supports multiversioning of functions,
   /// which requires support for cpu_supports and cpu_is functionality.
   bool supportsMultiVersioning() const { return getTriple().isX86(); }
 
   /// Identify whether this target supports IFuncs.
-  bool supportsIFunc() const { return getTriple().isOSBinFormatELF(); }
+  bool supportsIFunc() const {
+    return getTriple().isOSBinFormatELF() && !getTriple().isOSFuchsia();
+  }
 
   // Validate the contents of the __builtin_cpu_supports(const char*)
   // argument.
   virtual bool validateCpuSupports(StringRef Name) const { return false; }
 
   // Return the target-specific priority for features/cpus/vendors so
   // that they can be properly sorted for checking.
   virtual unsigned multiVersionSortPriority(StringRef Name) const {

clang/test/CodeGen/attr-target-mv-va-args.c

 // RUN: %clang_cc1 -no-opaque-pointers -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=LINUX
-// RUN: %clang_cc1 -no-opaque-pointers -triple x86_64-windows-pc -emit-llvm %s -o - | FileCheck %s --check-prefix=WINDOWS
+// RUN: %clang_cc1 -no-opaque-pointers -triple x86_64-windows-pc -emit-llvm %s -o - | FileCheck %s --check-prefixes=NO-IFUNC,WINDOWS
+// RUN: %clang_cc1 -no-opaque-pointers -triple x86_64-fuchsia -emit-llvm %s -o - | FileCheck %s --check-prefixes=NO-IFUNC,FUCHSIA
 int __attribute__((target("sse4.2"))) foo(int i, ...) { return 0; }
 int __attribute__((target("arch=sandybridge"))) foo(int i, ...);
 int __attribute__((target("arch=ivybridge"))) foo(int i, ...) {return 1;}
 int __attribute__((target("default"))) foo(int i, ...) { return 2; }
 
 int bar(void) {
   return foo(1, 'a', 1.1) + foo(2, 2.2, "asdf");
 }

 
 // LINUX: define weak_odr i32 (i32, ...)* @foo.resolver() comdat
 // LINUX: ret i32 (i32, ...)* @foo.arch_sandybridge
 // LINUX: ret i32 (i32, ...)* @foo.arch_ivybridge
 // LINUX: ret i32 (i32, ...)* @foo.sse4.2
 // LINUX: ret i32 (i32, ...)* @foo
 // LINUX: declare i32 @foo.arch_sandybridge(i32 noundef, ...)
 
-// WINDOWS: define dso_local i32 @foo.sse4.2(i32 noundef %i, ...)
-// WINDOWS: ret i32 0
-// WINDOWS: define dso_local i32 @foo.arch_ivybridge(i32 noundef %i, ...)
-// WINDOWS: ret i32 1
-// WINDOWS: define dso_local i32 @foo(i32 noundef %i, ...)
-// WINDOWS: ret i32 2
-// WINDOWS: define dso_local i32 @bar()
-// WINDOWS: call i32 (i32, ...) @foo.resolver(i32 noundef 1, i32 noundef 97, double
-// WINDOWS: call i32 (i32, ...) @foo.resolver(i32 noundef 2, double noundef 2.2{{[0-9Ee+]+}}, i8* noundef getelementptr inbounds
+// NO-IFUNC: define dso_local i32 @foo.sse4.2(i32 noundef %i, ...)
+// NO-IFUNC: ret i32 0
+// NO-IFUNC: define dso_local i32 @foo.arch_ivybridge(i32 noundef %i, ...)
+// NO-IFUNC: ret i32 1
+// NO-IFUNC: define dso_local i32 @foo(i32 noundef %i, ...)
+// NO-IFUNC: ret i32 2
+// NO-IFUNC: define dso_local i32 @bar()
+// NO-IFUNC: call i32 (i32, ...) @foo.resolver(i32 noundef 1, i32 noundef 97, double
+// NO-IFUNC: call i32 (i32, ...) @foo.resolver(i32 noundef 2, double noundef 2.2{{[0-9Ee+]+}}, i8* noundef getelementptr inbounds
 
 // WINDOWS: define weak_odr dso_local i32 @foo.resolver(i32 %0, ...) comdat
-// WINDOWS: musttail call i32 (i32, ...) @foo.arch_sandybridge
-// WINDOWS: musttail call i32 (i32, ...) @foo.arch_ivybridge
-// WINDOWS: musttail call i32 (i32, ...) @foo.sse4.2
-// WINDOWS: musttail call i32 (i32, ...) @foo
+// FUCHSIA: define weak_odr i32 @foo.resolver(i32 %0, ...) comdat
+// NO-IFUNC: musttail call i32 (i32, ...) @foo.arch_sandybridge
+// NO-IFUNC: musttail call i32 (i32, ...) @foo.arch_ivybridge
+// NO-IFUNC: musttail call i32 (i32, ...) @foo.sse4.2
+// NO-IFUNC: musttail call i32 (i32, ...) @foo
 // WINDOWS: declare dso_local i32 @foo.arch_sandybridge(i32 noundef, ...)
+// FUCHSIA: declare i32 @foo.arch_sandybridge(i32 noundef, ...)