Index: llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -856,6 +856,7 @@
   bool parseDirectiveFPOEndProc(SMLoc L);
   bool parseDirectiveFPOData(SMLoc L);
 
+  bool validateInstruction(MCInst &Inst, const OperandVector &Ops);
   bool processInstruction(MCInst &Inst, const OperandVector &Ops);
 
   /// Wrapper around MCStreamer::EmitInstruction(). Possibly adds
@@ -2627,6 +2628,72 @@
   return false;
 }
 
+bool X86AsmParser::validateInstruction(MCInst &Inst, const OperandVector &Ops) {
+  const MCRegisterInfo *MRI = getContext().getRegisterInfo();
+
+  switch (Inst.getOpcode()) {
+  case X86::VGATHERDPDYrm:
+  case X86::VGATHERDPDrm:
+  case X86::VGATHERDPSYrm:
+  case X86::VGATHERDPSrm:
+  case X86::VGATHERQPDYrm:
+  case X86::VGATHERQPDrm:
+  case X86::VGATHERQPSYrm:
+  case X86::VGATHERQPSrm:
+  case X86::VPGATHERDDYrm:
+  case X86::VPGATHERDDrm:
+  case X86::VPGATHERDQYrm:
+  case X86::VPGATHERDQrm:
+  case X86::VPGATHERQDYrm:
+  case X86::VPGATHERQDrm:
+  case X86::VPGATHERQQYrm:
+  case X86::VPGATHERQQrm: {
+    unsigned Dest = MRI->getEncodingValue(Inst.getOperand(0).getReg());
+    unsigned Mask = MRI->getEncodingValue(Inst.getOperand(1).getReg());
+    unsigned Index =
+      MRI->getEncodingValue(Inst.getOperand(3 + X86::AddrIndexReg).getReg());
+    if (Dest == Mask || Dest == Index || Mask == Index)
+      return Warning(Ops[0]->getStartLoc(), "mask, index, and destination "
+                                            "registers should be distinct");
+    break;
+  }
+  case X86::VGATHERDPDZ128rm:
+  case X86::VGATHERDPDZ256rm:
+  case X86::VGATHERDPDZrm:
+  case X86::VGATHERDPSZ128rm:
+  case X86::VGATHERDPSZ256rm:
+  case X86::VGATHERDPSZrm:
+  case X86::VGATHERQPDZ128rm:
+  case X86::VGATHERQPDZ256rm:
+  case X86::VGATHERQPDZrm:
+  case X86::VGATHERQPSZ128rm:
+  case X86::VGATHERQPSZ256rm:
+  case X86::VGATHERQPSZrm:
+  case X86::VPGATHERDDZ128rm:
+  case X86::VPGATHERDDZ256rm:
+  case X86::VPGATHERDDZrm:
+  case X86::VPGATHERDQZ128rm:
+  case X86::VPGATHERDQZ256rm:
+  case X86::VPGATHERDQZrm:
+  case X86::VPGATHERQDZ128rm:
+  case X86::VPGATHERQDZ256rm:
+  case X86::VPGATHERQDZrm:
+  case X86::VPGATHERQQZ128rm:
+  case X86::VPGATHERQQZ256rm:
+  case X86::VPGATHERQQZrm: {
+    unsigned Dest = MRI->getEncodingValue(Inst.getOperand(0).getReg());
+    unsigned Index =
+      MRI->getEncodingValue(Inst.getOperand(4 + X86::AddrIndexReg).getReg());
+    if (Dest == Index)
+      return Warning(Ops[0]->getStartLoc(), "index and destination registers "
+                                            "should be distinct");
+    break;
+  }
+  }
+
+  return false;
+}
+
 static const char *getSubtargetFeatureName(uint64_t Val);
 
 void X86AsmParser::EmitInstruction(MCInst &Inst, OperandVector &Operands,
@@ -2723,6 +2790,8 @@
                            isParsingIntelSyntax())) {
   default: llvm_unreachable("Unexpected match result!");
   case Match_Success:
+    if (validateInstruction(Inst, Operands))
+      return true;
     // Some instructions need post-processing to, for example, tweak which
     // encoding is selected. Loop on it while changes happen so the
     // individual transformations can chain off each other.
@@ -3012,6 +3081,8 @@
   // instruction will already have been filled in correctly, since the failing
   // matches won't have modified it).
   if (NumSuccessfulMatches == 1) {
+    if (validateInstruction(Inst, Operands))
+      return true;
     // Some instructions need post-processing to, for example, tweak which
     // encoding is selected. Loop on it while changes happen so the individual
     // transformations can chain off each other.
Index: llvm/trunk/test/MC/X86/gather.s
===================================================================
--- llvm/trunk/test/MC/X86/gather.s
+++ llvm/trunk/test/MC/X86/gather.s
@@ -0,0 +1,19 @@
+// RUN: llvm-mc -triple x86_64-unknown-unknown -mattr=avx512f -show-encoding %s > %t 2> %t.err
+// RUN: FileCheck < %t %s
+// RUN: FileCheck --check-prefix=CHECK-STDERR < %t.err %s
+
+// CHECK: vgatherdps %xmm2, (%rdi,%xmm2,2), %xmm2
+// CHECK-STDERR: warning: mask, index, and destination registers should be distinct
+vgatherdps %xmm2, (%rdi,%xmm2,2), %xmm2
+
+// CHECK: vpgatherdd (%r14,%zmm11,8), %zmm11 {%k1}
+// CHECK-STDERR: warning: index and destination registers should be distinct
+vpgatherdd (%r14, %zmm11,8), %zmm11 {%k1}
+
+// CHECK: vpgatherqd (%r14,%zmm11,8), %ymm11 {%k1}
+// CHECK-STDERR: warning: index and destination registers should be distinct
+vpgatherqd (%r14, %zmm11,8), %ymm11 {%k1}
+
+// CHECK: vpgatherdq (%r14,%ymm11,8), %zmm11 {%k1}
+// CHECK-STDERR: warning: index and destination registers should be distinct
+vpgatherdq (%r14, %ymm11,8), %zmm11 {%k1}