diff --git a/clang/lib/Headers/ia32intrin.h b/clang/lib/Headers/ia32intrin.h
--- a/clang/lib/Headers/ia32intrin.h
+++ b/clang/lib/Headers/ia32intrin.h
@@ -413,6 +413,58 @@
 
 #ifndef _MSC_VER
 /* These are already provided as builtins for MSVC. */
+#define _BitScanForward(a, b)                                                  \
+  __extension__({                                                              \
+    int c = (int)(b);                                                          \
+    unsigned char d;                                                           \
+    if (c != 0) {                                                              \
+      *(a) = (unsigned)__bsfd(c);                                              \
+      d = 1;                                                                   \
+    } else {                                                                   \
+      d = 0;                                                                   \
+    }                                                                          \
+    d;                                                                         \
+  })
+#define _BitScanReverse(a, b)                                                  \
+  __extension__({                                                              \
+    int c = (int)(b);                                                          \
+    unsigned char d;                                                           \
+    if (c != 0) {                                                              \
+      *(a) = (unsigned)__bsrd(c);                                              \
+      d = 1;                                                                   \
+    } else {                                                                   \
+      d = 0;                                                                   \
+    }                                                                          \
+    d;                                                                         \
+  })
+
+#ifdef __x86_64__
+#define _BitScanForward64(a, b)                                                \
+  __extension__({                                                              \
+    long long c = (long long)(b);                                              \
+    unsigned char d;                                                           \
+    if (c != 0) {                                                              \
+      *(a) = (unsigned)__bsfq(c);                                              \
+      d = 1;                                                                   \
+    } else {                                                                   \
+      d = 0;                                                                   \
+    }                                                                          \
+    d;                                                                         \
+  })
+#define _BitScanReverse64(a, b)                                                \
+  __extension__({                                                              \
+    long long c = (long long)(b);                                              \
+    unsigned char d;                                                           \
+    if (c != 0) {                                                              \
+      *(a) = (unsigned)__bsrq(c);                                              \
+      d = 1;                                                                   \
+    } else {                                                                   \
+      d = 0;                                                                   \
+    }                                                                          \
+    d;                                                                         \
+  })
+#endif /* __x86_64__ */
+
 /* Select the correct function based on the size of long. */
 #ifdef __LP64__
 #define _lrotl(a,b) __rolq((a), (b))
diff --git a/clang/test/CodeGen/bitscan-builtins.c b/clang/test/CodeGen/bitscan-builtins.c
--- a/clang/test/CodeGen/bitscan-builtins.c
+++ b/clang/test/CodeGen/bitscan-builtins.c
@@ -5,6 +5,32 @@
 
 #include <x86intrin.h>
 
+unsigned char test_BitScanForward(unsigned *index, unsigned mask) {
+  return _BitScanForward(index, mask);
+  // CHECK: @test_BitScanForward
+  // CHECK: %{{.*}} = call i32 @llvm.cttz.i32(i32 %{{.*}}, i1 true)
+}
+
+unsigned char test_BitScanReverse(unsigned *index, unsigned mask) {
+  return _BitScanReverse(index, mask);
+  // CHECK: @test_BitScanReverse
+  // CHECK:  %[[call:.*]] = call i32 @llvm.ctlz.i32(i32 %{{.*}}, i1 true)
+  // CHECK:  %{{.*}} = sub nsw i32 31, %[[call]]
+}
+
+unsigned char test_BitScanForward64(unsigned *index, unsigned long long mask) {
+  return _BitScanForward64(index, mask);
+  // CHECK: @test_BitScanForward64
+  // CHECK: %{{.*}} = call i64 @llvm.cttz.i64(i64 %{{.*}}, i1 true)
+}
+
+unsigned char test_BitScanReverse64(unsigned *index, unsigned long long mask) {
+  return _BitScanReverse64(index, mask);
+  // CHECK: @test_BitScanReverse64
+  // CHECK:  %{{.*}} = call i64 @llvm.ctlz.i64(i64 %{{.*}}, i1 true)
+  // CHECK:  %{{.*}} = sub nsw i32 63, %{{.*}}
+}
+
 int test_bit_scan_forward(int a) {
   return _bit_scan_forward(a);
 // CHECK: @test_bit_scan_forward