diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -384,6 +384,9 @@
   "argument '%0' is deprecated, use '%1' instead">, InGroup<Deprecated>;
 def warn_drv_assuming_mfloat_abi_is : Warning<
   "unknown platform, assuming -mfloat-abi=%0">;
+def warn_drv_unsupported_float_abi_by_cxxlib : Warning<
+  "float ABI '%0' is not supported by current C++ stdlib">,
+  InGroup<DiagGroup<"unsupported-cxxlib">>;
 def warn_ignoring_ftabstop_value : Warning<
   "ignoring invalid -ftabstop value '%0', using default value %1">;
 def warn_drv_overriding_flag_option : Warning<
diff --git a/clang/lib/Driver/ToolChains/PPCLinux.h b/clang/lib/Driver/ToolChains/PPCLinux.h
--- a/clang/lib/Driver/ToolChains/PPCLinux.h
+++ b/clang/lib/Driver/ToolChains/PPCLinux.h
@@ -18,8 +18,7 @@
 class LLVM_LIBRARY_VISIBILITY PPCLinuxToolChain : public Linux {
 public:
   PPCLinuxToolChain(const Driver &D, const llvm::Triple &Triple,
-                    const llvm::opt::ArgList &Args)
-      : Linux(D, Triple, Args) {}
+                    const llvm::opt::ArgList &Args);
 
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
diff --git a/clang/lib/Driver/ToolChains/PPCLinux.cpp b/clang/lib/Driver/ToolChains/PPCLinux.cpp
--- a/clang/lib/Driver/ToolChains/PPCLinux.cpp
+++ b/clang/lib/Driver/ToolChains/PPCLinux.cpp
@@ -8,12 +8,28 @@
 
 #include "PPCLinux.h"
 #include "clang/Driver/Driver.h"
+#include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Support/Path.h"
 
 using namespace clang::driver::toolchains;
 using namespace llvm::opt;
 
+PPCLinuxToolChain::PPCLinuxToolChain(const Driver &D,
+                                     const llvm::Triple &Triple,
+                                     const llvm::opt::ArgList &Args)
+    : Linux(D, Triple, Args) {
+  if (D.CCCIsCXX() && (ToolChain::GetCXXStdlibType(Args) == CST_Libcxx ||
+                       GCCInstallation.getVersion().isOlderThan(12, 1, 0))) {
+    if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
+      StringRef ABIName = A->getValue();
+      if (ABIName != "ibmlongdouble") {
+        D.Diag(diag::warn_drv_unsupported_float_abi_by_cxxlib) << ABIName;
+      }
+    }
+  }
+}
+
 void PPCLinuxToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                                   ArgStringList &CC1Args) const {
   if (!DriverArgs.hasArg(clang::driver::options::OPT_nostdinc) &&
diff --git a/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib/gcc/powerpc64le-linux-gnu/11.2.0/.keep b/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib/gcc/powerpc64le-linux-gnu/11.2.0/.keep
new file mode 100644
diff --git a/clang/test/Driver/ppc-float-abi-warning.cpp b/clang/test/Driver/ppc-float-abi-warning.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/ppc-float-abi-warning.cpp
@@ -0,0 +1,13 @@
+// REQUIRES: powerpc-registered-target
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s \
+// RUN:  --gcc-toolchain=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0 \
+// RUN:  -mabi=ieeelongdouble -stdlib=libstdc++ 2>&1 | FileCheck %s
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s \
+// RUN:  -mabi=ieeelongdouble -stdlib=libc++ 2>&1 | FileCheck %s
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s\
+// RUN:  -mabi=ieeelongdouble -stdlib=libc++ -Wno-unsupported-cxxlib 2>&1 | \
+// RUN:  FileCheck %s --check-prefix=NOWARN
+
+// CHECK: warning: float ABI 'ieeelongdouble' is not supported by current C++ stdlib
+// NOWARN-NOT: warning: float ABI 'ieeelongdouble' is not supported by current C++ stdlib
+long double foo(long double x) { return x;  }