diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -237,6 +237,9 @@
 set(ENABLE_X86_RELAX_RELOCATIONS ON CACHE BOOL
     "enable x86 relax relocations by default")
 
+set(PPC_LINUX_DEFAULT_IEEELONGDOUBLE OFF CACHE BOOL
+    "Enable IEEE binary128 as default long double format on PowerPC Linux.")
+
 set(CLANG_SPAWN_CC1 OFF CACHE BOOL
     "Whether clang should use a new process for the CC1 invocation")
 
diff --git a/clang/include/clang/Config/config.h.cmake b/clang/include/clang/Config/config.h.cmake
--- a/clang/include/clang/Config/config.h.cmake
+++ b/clang/include/clang/Config/config.h.cmake
@@ -78,6 +78,9 @@
 /* enable x86 relax relocations by default */
 #cmakedefine01 ENABLE_X86_RELAX_RELOCATIONS
 
+/* Enable IEEE binary128 as default long double format on PowerPC Linux. */
+#cmakedefine01 PPC_LINUX_DEFAULT_IEEELONGDOUBLE
+
 /* Enable each functionality of modules */
 #cmakedefine01 CLANG_ENABLE_ARCMT
 #cmakedefine01 CLANG_ENABLE_OBJC_REWRITER
diff --git a/clang/include/clang/Driver/ToolChain.h b/clang/include/clang/Driver/ToolChain.h
--- a/clang/include/clang/Driver/ToolChain.h
+++ b/clang/include/clang/Driver/ToolChain.h
@@ -409,6 +409,9 @@
   /// Check whether to enable x86 relax relocations by default.
   virtual bool useRelaxRelocations() const;
 
+  /// Check whether use IEEE binary128 as long double format by default.
+  bool defaultToIEEELongDouble() const;
+
   /// GetDefaultStackProtectorLevel - Get the default stack protector level for
   /// this tool chain.
   virtual LangOptions::StackProtectorMode
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -109,6 +109,10 @@
   return ENABLE_X86_RELAX_RELOCATIONS;
 }
 
+bool ToolChain::defaultToIEEELongDouble() const {
+  return PPC_LINUX_DEFAULT_IEEELONGDOUBLE && getTriple().isOSLinux();
+}
+
 SanitizerArgs
 ToolChain::getSanitizerArgs(const llvm::opt::ArgList &JobArgs) const {
   SanitizerArgs SanArgs(*this, JobArgs, !SanitizerArgsChecked);
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2061,7 +2061,7 @@
     }
   }
 
-  bool IEEELongDouble = false;
+  bool IEEELongDouble = getToolChain().defaultToIEEELongDouble();
   for (const Arg *A : Args.filtered(options::OPT_mabi_EQ)) {
     StringRef V = A->getValue();
     if (V == "ieeelongdouble")
diff --git a/clang/test/Analysis/builtin_signbit.cpp b/clang/test/Analysis/builtin_signbit.cpp
--- a/clang/test/Analysis/builtin_signbit.cpp
+++ b/clang/test/Analysis/builtin_signbit.cpp
@@ -1,6 +1,9 @@
-// RUN: %clang -target powerpc-linux-gnu     -emit-llvm -S -O0 %s -o - | FileCheck %s --check-prefix=CHECK-BE --check-prefix=CHECK
-// RUN: %clang -target powerpc64-linux-gnu   -emit-llvm -S -O0 %s -o - | FileCheck %s --check-prefix=CHECK-BE --check-prefix=CHECK
-// RUN: %clang -target powerpc64le-linux-gnu -emit-llvm -S -O0 %s -o - | FileCheck %s --check-prefix=CHECK-LE --check-prefix=CHECK
+// RUN: %clang -target powerpc-linux-gnu -emit-llvm -S -mabi=ibmlongdouble \
+// RUN:   -O0 %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang -target powerpc64-linux-gnu -emit-llvm -S -mabi=ibmlongdouble \
+// RUN:   -O0 %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang -target powerpc64le-linux-gnu -emit-llvm -S -mabi=ibmlongdouble \
+// RUN:   -O0 %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-LE
 
 bool b;
 double d = -1.0;
diff --git a/clang/test/Driver/ppc-abi.c b/clang/test/Driver/ppc-abi.c
--- a/clang/test/Driver/ppc-abi.c
+++ b/clang/test/Driver/ppc-abi.c
@@ -63,9 +63,6 @@
 // CHECK-ELFv1-IEEE: "-mabi=ieeelongdouble"
 // CHECK-ELFv1-IEEE: "-target-abi" "elfv1"
 
-// Check -mabi=ibmlongdouble is the default.
-// RUN: %clang -target powerpc64le-linux-gnu %s -### 2>&1 \
-// RUN:   | FileCheck -check-prefix=CHECK-ELFv2-IBM128 %s
 // RUN: %clang -target powerpc64le-linux-gnu %s -mabi=ibmlongdouble -### 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-ELFv2-IBM128 %s