Index: docs/LibASTMatchersReference.html
===================================================================
--- docs/LibASTMatchersReference.html
+++ docs/LibASTMatchersReference.html
@@ -2789,15 +2789,19 @@
 
 
 <tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1FunctionDecl.html">FunctionDecl</a>&gt;</td><td class="name" onclick="toggle('isConstexpr1')"><a name="isConstexpr1Anchor">isConstexpr</a></td><td></td></tr>
-<tr><td colspan="4" class="doc" id="isConstexpr1"><pre>Matches constexpr variable and function declarations.
+<tr><td colspan="4" class="doc" id="isConstexpr1"><pre>Matches constexpr variable and function declarations,
+       and if constexpr.
 
 Given:
   constexpr int foo = 42;
   constexpr int bar();
+  void baz() { if constexpr(1 &gt; 0) {} }
 varDecl(isConstexpr())
   matches the declaration of foo.
 functionDecl(isConstexpr())
   matches the declaration of bar.
+ifStmt(isConstexpr())
+  matches the if statement in baz.
 </pre></td></tr>
 
 
@@ -3039,6 +3043,23 @@
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1IfStmt.html">IfStmt</a>&gt;</td><td class="name" onclick="toggle('isConstexpr2')"><a name="isConstexpr2Anchor">isConstexpr</a></td><td></td></tr>
+<tr><td colspan="4" class="doc" id="isConstexpr2"><pre>Matches constexpr variable and function declarations,
+       and if constexpr.
+
+Given:
+  constexpr int foo = 42;
+  constexpr int bar();
+  void baz() { if constexpr(1 &gt; 0) {} }
+varDecl(isConstexpr())
+  matches the declaration of foo.
+functionDecl(isConstexpr())
+  matches the declaration of bar.
+ifStmt(isConstexpr())
+  matches the if statement in baz.
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1IntegerLiteral.html">IntegerLiteral</a>&gt;</td><td class="name" onclick="toggle('equals6')"><a name="equals6Anchor">equals</a></td><td>bool Value</td></tr>
 <tr><td colspan="4" class="doc" id="equals6"><pre></pre></td></tr>
 
@@ -3803,15 +3824,19 @@
 
 
 <tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1VarDecl.html">VarDecl</a>&gt;</td><td class="name" onclick="toggle('isConstexpr0')"><a name="isConstexpr0Anchor">isConstexpr</a></td><td></td></tr>
-<tr><td colspan="4" class="doc" id="isConstexpr0"><pre>Matches constexpr variable and function declarations.
+<tr><td colspan="4" class="doc" id="isConstexpr0"><pre>Matches constexpr variable and function declarations,
+       and if constexpr.
 
 Given:
   constexpr int foo = 42;
   constexpr int bar();
+  void baz() { if constexpr(1 &gt; 0) {} }
 varDecl(isConstexpr())
   matches the declaration of foo.
 functionDecl(isConstexpr())
   matches the declaration of bar.
+ifStmt(isConstexpr())
+  matches the if statement in baz.
 </pre></td></tr>
 
 
Index: include/clang/ASTMatchers/ASTMatchers.h
===================================================================
--- include/clang/ASTMatchers/ASTMatchers.h
+++ include/clang/ASTMatchers/ASTMatchers.h
@@ -3763,20 +3763,25 @@
   return FnTy->isNothrow();
 }
 
-/// \brief Matches constexpr variable and function declarations.
+/// \brief Matches constexpr variable and function declarations,
+///        and if constexpr.
 ///
 /// Given:
 /// \code
 ///   constexpr int foo = 42;
 ///   constexpr int bar();
+///   void baz() { if constexpr(1 > 0) {} }
 /// \endcode
 /// varDecl(isConstexpr())
 ///   matches the declaration of foo.
 /// functionDecl(isConstexpr())
 ///   matches the declaration of bar.
+/// ifStmt(isConstexpr())
+///   matches the if statement in baz.
 AST_POLYMORPHIC_MATCHER(isConstexpr,
                         AST_POLYMORPHIC_SUPPORTED_TYPES(VarDecl,
-                                                        FunctionDecl)) {
+                                                        FunctionDecl,
+                                                        IfStmt)) {
   return Node.isConstexpr();
 }
 
Index: unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
===================================================================
--- unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
+++ unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
@@ -894,6 +894,10 @@
                       varDecl(hasName("foo"), isConstexpr())));
   EXPECT_TRUE(matches("constexpr int bar();",
                       functionDecl(hasName("bar"), isConstexpr())));
+  EXPECT_TRUE(matchesConditionally("void baz() { if constexpr(1 > 0) {} }",
+                                   ifStmt(isConstexpr()), true, "-std=c++17"));
+  EXPECT_TRUE(matchesConditionally("void baz() { if (1 > 0) {} }",
+                                   ifStmt(isConstexpr()), false, "-std=c++17"));
 }
 
 TEST(TemplateArgumentCountIs, Matches) {