Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -35623,8 +35623,14 @@
       switch (Constraint[1]) {
       default:
         break;
-      case 'k':
+      case 'z':
+      case '0':
         return C_Register;
+      case 'k':
+      case 'm':
+      case '2':
+      case 'i':
+        return C_RegisterClass;
       }
     }
   }
@@ -35673,10 +35679,29 @@
       weight = CW_SpecificReg;
     break;
   case 'Y':
-    // Other "Y<x>" (e.g. "Yk") constraints should be implemented below.
-    if (constraint[1] == 'k') {
-      // Support for 'Yk' (similarly to the 'k' variant below).
-      weight = CW_SpecificReg;
+    // "Y<x>" (e.g. "Yk") constraints should be implemented below.
+    switch(constraint[1]){
+    default:
+      break;
+    case 'z': // First SSE register xmm0
+    case '0':
+      if ((type->getPrimitiveSizeInBits() == 128) && Subtarget.hasSSE1())
+        weight = CW_SpecificReg;
+      break;
+    case '2': // Any SSE register when SSE2 is enabled
+    case 'i':
+      if ((type->getPrimitiveSizeInBits() == 128) && Subtarget.hasSSE2())
+        weight = CW_SpecificReg;
+      break;
+    case 'm': // Any MMX when "inter-unit moves" are enabled, a reference to
+              // gcc optimization directive for older AMD cpus.
+      if (type->isX86_MMXTy() && Subtarget.hasMMX())
+        weight = CW_SpecificReg;
+      break;
+      // Support for 'Yk' constraint, similarly to the 'k' variant below.
+      // Denotes specific use of %k1-k7.
+      case 'k':
+        weight = CW_SpecificReg;
       break;
     }
   // Else fall through (handle "Y" constraint).
@@ -36091,9 +36116,22 @@
       break;
     }
   } else if (Constraint.size() == 2 && Constraint[0] == 'Y') {
+    char EqualSingelCharConstraint;
     switch (Constraint[1]) {
     default:
       break;
+    case 'i': // Any SSE register when SSE2 is enabled (GCC).
+    case '2': // Any SSE register when SSE2 is enabled.
+    case 'm': // Any mmx register when inter-unit moves are enabled.
+      // These are practically identical to thier single letter counterparts.
+      // Map the double latter constraints to : 'Yi','Y2' -> 'Y' | 'Ym' -> 'y'
+      EqualSingelCharConstraint = (Constraint[1] == 'm' ? 'y': 'Y');
+      return getRegForInlineAsmConstraint(
+          TRI, StringRef(&EqualSingelCharConstraint, 1), VT);
+    case 'z': // %xmm0
+    case '0':
+      if (!Subtarget.hasSSE1()) break;
+      return std::make_pair(X86::XMM0, &X86::VR128RegClass);
     case 'k':
       // This register class doesn't allocate k0 for masked vector operation.
       if (Subtarget.hasAVX512()) { // Only supported in AVX512.
Index: test/MC/X86/x86-GCC-inline-asm-Y-constraints.ll
===================================================================
--- test/MC/X86/x86-GCC-inline-asm-Y-constraints.ll
+++ test/MC/X86/x86-GCC-inline-asm-Y-constraints.ll
@@ -0,0 +1,69 @@
+; RUN: llc -mtriple=x86_64-apple-darwin -mcpu skx < %s | FileCheck %s
+; This test compliments the .c test under clang/test/CodeGen/. We check 
+; if the inline asm constraints are respected in the generated code.
+
+; Function Attrs: nounwind
+define void @f_Ym(i64 %m.coerce) {
+; Any mmx regiter constraint
+; CHECK-LABEL: f_Ym:
+; CHECK:         ## InlineAsm Start
+; CHECK-NEXT:    movq %mm{{[0-9]+}}, %mm1
+; CHECK:         ## InlineAsm End
+
+entry:
+  %0 = tail call x86_mmx asm sideeffect "movq $0, %mm1\0A\09", "=^Ym,~{dirflag},~{fpsr},~{flags}"() 
+  ret void
+}
+
+; Function Attrs: nounwind
+define void @f_Yi(<4 x float> %x, <4 x float> %y, <4 x float> %z) {
+; Any SSE register when SSE2 is enabled (GCC when inter-unit moves enabled)
+; CHECK-LABEL: f_Yi:
+; CHECK:         ## InlineAsm Start
+; CHECK-NEXT:    vpaddq %xmm{{[0-9]+}}, %xmm{{[0-9]+}}, %xmm{{[0-9]+}}
+; CHECK:         ## InlineAsm End
+
+entry:
+  %0 = tail call <4 x float> asm sideeffect "vpaddq $0, $1, $2\0A\09", "=^Yi,^Yi,^Yi,~{dirflag},~{fpsr},~{flags}"(<4 x float> %y, <4 x float> %z) 
+  ret void
+}
+
+; Function Attrs: nounwind
+define void @f_Y2(<4 x float> %x, <4 x float> %y, <4 x float> %z) {
+; Any SSE register when SSE2 is enabled
+; CHECK-LABEL: f_Y2:
+; CHECK:         ## InlineAsm Start
+; CHECK-NEXT:    vpaddq %xmm{{[0-9]+}}, %xmm{{[0-9]+}}, %xmm{{[0-9]+}}
+; CHECK:         ## InlineAsm End
+
+entry:
+  %0 = tail call <4 x float> asm sideeffect "vpaddq $0, $1, $2\0A\09", "=^Y2,^Y2,^Y2,~{dirflag},~{fpsr},~{flags}"(<4 x float> %y, <4 x float> %z)
+  ret void
+}
+
+; Function Attrs: nounwind
+define void @f_Yz(<4 x float> %x, <4 x float> %y, <4 x float> %z) {
+; xmm0 SSE register(GCC)
+; CHECK-LABEL: f_Yz:
+; CHECK:         ## InlineAsm Start
+; CHECK-NEXT:    vpaddq %xmm{{[0-9]+}}, %xmm{{[0-9]+}}, %xmm0
+; CHECK-NEXT:    vpaddq %xmm0, %xmm{{[0-9]+}}, %xmm{{[0-9]+}}
+; CHECK:         ## InlineAsm End
+entry:
+  %0 = tail call { <4 x float>, <4 x float> } asm sideeffect "vpaddq $0,$2,$1\0A\09vpaddq $1,$0,$2\0A\09", "=^Yi,=^Yz,^Yi,0,~{dirflag},~{fpsr},~{flags}"(<4 x float> %y, <4 x float> %z)
+  ret void
+}
+
+; Function Attrs: nounwind
+define void @f_Y0(<4 x float> %x, <4 x float> %y, <4 x float> %z) {
+; xmm0 SSE register
+; CHECK-LABEL: f_Y0:
+; CHECK:         ## InlineAsm Start
+; CHECK-NEXT:    vpaddq %xmm{{[0-9]+}}, %xmm{{[0-9]+}}, %xmm0
+; CHECK-NEXT:    vpaddq %xmm0, %xmm{{[0-9]+}}, %xmm{{[0-9]+}}
+; CHECK:         ## InlineAsm End
+
+entry:
+  %0 = tail call { <4 x float>, <4 x float> } asm sideeffect "vpaddq $0,$2,$1\0A\09vpaddq $1,$0,$2\0A\09", "=^Yi,=^Y0,^Yi,0,~{dirflag},~{fpsr},~{flags}"(<4 x float> %y, <4 x float> %z)
+  ret void
+}
\ No newline at end of file