diff --git a/clang/lib/Headers/usermsrintrin.h b/clang/lib/Headers/usermsrintrin.h
index 6d1424ad3b2edd..61388376706dc6 100644
--- a/clang/lib/Headers/usermsrintrin.h
+++ b/clang/lib/Headers/usermsrintrin.h
@@ -14,12 +14,33 @@
 #define __USERMSRINTRIN_H
 #ifdef __x86_64__
 
+/// Reads the contents of a 64-bit MSR specified in \a __A into \a dst.
+///
+/// This intrinsic corresponds to the <c> URDMSR </c> instruction.
+/// \param __A
+///    An unsigned long long.
+///
+/// \code{.operation}
+///    DEST := MSR[__A]
+/// \endcode
 static __inline__ unsigned long long
     __attribute__((__always_inline__, __nodebug__, __target__("usermsr")))
     _urdmsr(unsigned long long __A) {
   return __builtin_ia32_urdmsr(__A);
 }
 
+/// Writes the contents of \a __B into the 64-bit MSR specified in \a __A.
+///
+/// This intrinsic corresponds to the <c> UWRMSR </c> instruction.
+///
+/// \param __A
+///    An unsigned long long.
+/// \param __B
+///    An unsigned long long.
+///
+/// \code{.operation}
+///    MSR[__A] := __B
+/// \endcode
 static __inline__ void
     __attribute__((__always_inline__, __nodebug__, __target__("usermsr")))
     _uwrmsr(unsigned long long __A, unsigned long long __B) {
diff --git a/llvm/lib/Target/X86/X86InstrSystem.td b/llvm/lib/Target/X86/X86InstrSystem.td
index efb58c6102dd1d..699e5847e63fb9 100644
--- a/llvm/lib/Target/X86/X86InstrSystem.td
+++ b/llvm/lib/Target/X86/X86InstrSystem.td
@@ -446,11 +446,11 @@ let Predicates = [HasUSERMSR], mayLoad = 1 in {
 }
 let Predicates = [HasUSERMSR], mayStore = 1 in {
   def UWRMSRrr : I<0xf8, MRMSrcReg, (outs), (ins GR64:$src1, GR64:$src2),
-                "uwrmsr\t{$src1, $src2|$src2, $src1}",
+                "uwrmsr\t{$src2, $src1|$src1, $src2}",
                 [(int_x86_uwrmsr GR64:$src1, GR64:$src2)]>, T8, XS;
   def UWRMSRir : Ii32<0xf8, MRM0r, (outs), (ins GR64:$src, i64i32imm:$imm),
                 "uwrmsr\t{$src, $imm|$imm, $src}",
-                [(int_x86_uwrmsr GR64:$src, i64immSExt32_su:$imm)]>, T_MAP7, XS, VEX;
+                [(int_x86_uwrmsr i64immSExt32_su:$imm, GR64:$src)]>, T_MAP7, XS, VEX;
 }
 let Defs = [RAX, RDX], Uses = [ECX] in
 def RDPMC : I<0x33, RawFrm, (outs), (ins), "rdpmc", []>, TB;
diff --git a/llvm/test/CodeGen/X86/usermsr-intrinsics.ll b/llvm/test/CodeGen/X86/usermsr-intrinsics.ll
index 29801a494f498f..fa569affdd9ff3 100644
--- a/llvm/test/CodeGen/X86/usermsr-intrinsics.ll
+++ b/llvm/test/CodeGen/X86/usermsr-intrinsics.ll
@@ -35,7 +35,7 @@ declare i64 @llvm.x86.urdmsr(i64 %A)
 define void @test_int_x86_uwrmsr(i64 %A, i64 %B) nounwind {
 ; X64-LABEL: test_int_x86_uwrmsr:
 ; X64:       # %bb.0:
-; X64-NEXT:    uwrmsr %rdi, %rsi # encoding: [0xf3,0x0f,0x38,0xf8,0xfe]
+; X64-NEXT:    uwrmsr %rsi, %rdi # encoding: [0xf3,0x0f,0x38,0xf8,0xfe]
 ; X64-NEXT:    retq # encoding: [0xc3]
   call void @llvm.x86.uwrmsr(i64 %A, i64 %B)
   ret void
@@ -46,7 +46,7 @@ define void @test_int_x86_uwrmsr_const(i64 %A) nounwind {
 ; X64:       # %bb.0:
 ; X64-NEXT:    uwrmsr %rdi, $123 # encoding: [0xc4,0xe7,0x7a,0xf8,0xc7,0x7b,0x00,0x00,0x00]
 ; X64-NEXT:    retq # encoding: [0xc3]
-  call void @llvm.x86.uwrmsr(i64 %A, i64 123)
+  call void @llvm.x86.uwrmsr(i64 123, i64 %A)
   ret void
 }
 
@@ -55,9 +55,9 @@ define void @test_int_x86_uwrmsr_const_i64(i64 %A) nounwind {
 ; X64:       # %bb.0:
 ; X64-NEXT:    movabsq $8589934591, %rax # encoding: [0x48,0xb8,0xff,0xff,0xff,0xff,0x01,0x00,0x00,0x00]
 ; X64-NEXT:    # imm = 0x1FFFFFFFF
-; X64-NEXT:    uwrmsr %rdi, %rax # encoding: [0xf3,0x0f,0x38,0xf8,0xf8]
+; X64-NEXT:    uwrmsr %rdi, %rax # encoding: [0xf3,0x0f,0x38,0xf8,0xc7]
 ; X64-NEXT:    retq # encoding: [0xc3]
-  call void @llvm.x86.uwrmsr(i64 %A, i64 8589934591)
+  call void @llvm.x86.uwrmsr(i64 8589934591, i64 %A)
   ret void
 }