Index: test/MC/X86/PREFETCH-32.s
===================================================================
--- /dev/null
+++ test/MC/X86/PREFETCH-32.s
@@ -0,0 +1,50 @@
+// RUN: llvm-mc -triple i386-unknown-unknown --show-encoding %s | FileCheck %s
+
+// CHECK: prefetch -485498096(%edx,%eax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x84,0x82,0x10,0xe3,0x0f,0xe3]        
+prefetch -485498096(%edx,%eax,4) 
+
+// CHECK: prefetch 485498096(%edx,%eax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x84,0x82,0xf0,0x1c,0xf0,0x1c]        
+prefetch 485498096(%edx,%eax,4) 
+
+// CHECK: prefetch 485498096(%edx) 
+// CHECK: encoding: [0x0f,0x0d,0x82,0xf0,0x1c,0xf0,0x1c]        
+prefetch 485498096(%edx) 
+
+// CHECK: prefetch 485498096 
+// CHECK: encoding: [0x0f,0x0d,0x05,0xf0,0x1c,0xf0,0x1c]        
+prefetch 485498096 
+
+// CHECK: prefetch 64(%edx,%eax) 
+// CHECK: encoding: [0x0f,0x0d,0x44,0x02,0x40]        
+prefetch 64(%edx,%eax) 
+
+// CHECK: prefetch (%edx) 
+// CHECK: encoding: [0x0f,0x0d,0x02]        
+prefetch (%edx) 
+
+// CHECK: prefetchw -485498096(%edx,%eax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x8c,0x82,0x10,0xe3,0x0f,0xe3]        
+prefetchw -485498096(%edx,%eax,4) 
+
+// CHECK: prefetchw 485498096(%edx,%eax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x8c,0x82,0xf0,0x1c,0xf0,0x1c]        
+prefetchw 485498096(%edx,%eax,4) 
+
+// CHECK: prefetchw 485498096(%edx) 
+// CHECK: encoding: [0x0f,0x0d,0x8a,0xf0,0x1c,0xf0,0x1c]        
+prefetchw 485498096(%edx) 
+
+// CHECK: prefetchw 485498096 
+// CHECK: encoding: [0x0f,0x0d,0x0d,0xf0,0x1c,0xf0,0x1c]        
+prefetchw 485498096 
+
+// CHECK: prefetchw 64(%edx,%eax) 
+// CHECK: encoding: [0x0f,0x0d,0x4c,0x02,0x40]        
+prefetchw 64(%edx,%eax) 
+
+// CHECK: prefetchw (%edx) 
+// CHECK: encoding: [0x0f,0x0d,0x0a]        
+prefetchw (%edx) 
+
Index: test/MC/X86/PREFETCH-64.s
===================================================================
--- /dev/null
+++ test/MC/X86/PREFETCH-64.s
@@ -0,0 +1,50 @@
+// RUN: llvm-mc -triple x86_64-unknown-unknown --show-encoding %s | FileCheck %s
+
+// CHECK: prefetch 485498096 
+// CHECK: encoding: [0x0f,0x0d,0x04,0x25,0xf0,0x1c,0xf0,0x1c]        
+prefetch 485498096 
+
+// CHECK: prefetch 64(%rdx) 
+// CHECK: encoding: [0x0f,0x0d,0x42,0x40]        
+prefetch 64(%rdx) 
+
+// CHECK: prefetch 64(%rdx,%rax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x44,0x82,0x40]        
+prefetch 64(%rdx,%rax,4) 
+
+// CHECK: prefetch -64(%rdx,%rax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x44,0x82,0xc0]        
+prefetch -64(%rdx,%rax,4) 
+
+// CHECK: prefetch 64(%rdx,%rax) 
+// CHECK: encoding: [0x0f,0x0d,0x44,0x02,0x40]        
+prefetch 64(%rdx,%rax) 
+
+// CHECK: prefetch (%rdx) 
+// CHECK: encoding: [0x0f,0x0d,0x02]        
+prefetch (%rdx) 
+
+// CHECK: prefetchw 485498096 
+// CHECK: encoding: [0x0f,0x0d,0x0c,0x25,0xf0,0x1c,0xf0,0x1c]        
+prefetchw 485498096 
+
+// CHECK: prefetchw 64(%rdx) 
+// CHECK: encoding: [0x0f,0x0d,0x4a,0x40]        
+prefetchw 64(%rdx) 
+
+// CHECK: prefetchw 64(%rdx,%rax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x4c,0x82,0x40]        
+prefetchw 64(%rdx,%rax,4) 
+
+// CHECK: prefetchw -64(%rdx,%rax,4) 
+// CHECK: encoding: [0x0f,0x0d,0x4c,0x82,0xc0]        
+prefetchw -64(%rdx,%rax,4) 
+
+// CHECK: prefetchw 64(%rdx,%rax) 
+// CHECK: encoding: [0x0f,0x0d,0x4c,0x02,0x40]        
+prefetchw 64(%rdx,%rax) 
+
+// CHECK: prefetchw (%rdx) 
+// CHECK: encoding: [0x0f,0x0d,0x0a]        
+prefetchw (%rdx) 
+