Index: llvm/trunk/lib/Target/X86/X86InsertPrefetch.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/X86InsertPrefetch.cpp
+++ llvm/trunk/lib/Target/X86/X86InsertPrefetch.cpp
@@ -76,6 +76,19 @@
   return std::error_code();
 }
 
+// The prefetch instruction can't take memory operands involving vector
+// registers.
+bool IsMemOpCompatibleWithPrefetch(const MachineInstr &MI, int Op) {
+  unsigned BaseReg = MI.getOperand(Op + X86::AddrBaseReg).getReg();
+  unsigned IndexReg = MI.getOperand(Op + X86::AddrIndexReg).getReg();
+  return (BaseReg == 0 ||
+          X86MCRegisterClasses[X86::GR64RegClassID].contains(BaseReg) ||
+          X86MCRegisterClasses[X86::GR32RegClassID].contains(BaseReg)) &&
+         (IndexReg == 0 ||
+          X86MCRegisterClasses[X86::GR64RegClassID].contains(IndexReg) ||
+          X86MCRegisterClasses[X86::GR32RegClassID].contains(IndexReg));
+}
+
 } // end anonymous namespace
 
 //===----------------------------------------------------------------------===//
@@ -182,6 +195,11 @@
       int Offset = X86II::getMemoryOperandNo(Current->getDesc().TSFlags);
       if (Offset < 0)
         continue;
+      unsigned Bias = X86II::getOperandBias(Current->getDesc());
+      int MemOpOffset = Offset + Bias;
+      // FIXME(mtrofin): ORE message when the recommendation cannot be taken.
+      if (!IsMemOpCompatibleWithPrefetch(*Current, MemOpOffset))
+        continue;
       Prefetches.clear();
       if (!findPrefetchInfo(Samples, *Current, Prefetches))
         continue;
@@ -195,8 +213,6 @@
         MachineInstr *PFetch =
             MF.CreateMachineInstr(Desc, Current->getDebugLoc(), true);
         MachineInstrBuilder MIB(MF, PFetch);
-        unsigned Bias = X86II::getOperandBias(Current->getDesc());
-        int MemOpOffset = Offset + Bias;
 
         assert(X86::AddrBaseReg == 0 && X86::AddrScaleAmt == 1 &&
                X86::AddrIndexReg == 2 && X86::AddrDisp == 3 &&
Index: llvm/trunk/test/CodeGen/X86/insert-prefetch-invalid-instr.afdo
===================================================================
--- llvm/trunk/test/CodeGen/X86/insert-prefetch-invalid-instr.afdo
+++ llvm/trunk/test/CodeGen/X86/insert-prefetch-invalid-instr.afdo
@@ -0,0 +1,2 @@
+main:0:0
+ 6: 0 __prefetch_nta_0:42
\ No newline at end of file
Index: llvm/trunk/test/CodeGen/X86/insert-prefetch-invalid-instr.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/insert-prefetch-invalid-instr.ll
+++ llvm/trunk/test/CodeGen/X86/insert-prefetch-invalid-instr.ll
@@ -0,0 +1,46 @@
+; RUN: llc < %s -prefetch-hints-file=%S/insert-prefetch-invalid-instr.afdo | FileCheck %s
+; ModuleID = 'prefetch.cc'
+source_filename = "prefetch.cc"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: norecurse nounwind uwtable
+define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
+entry:
+  tail call void @llvm.prefetch(i8* inttoptr (i64 291 to i8*), i32 0, i32 0, i32 1), !dbg !9
+  tail call void @llvm.x86.avx512.gatherpf.dpd.512(i8 97, <8 x i32> undef, i8* null, i32 1, i32 2), !dbg !10
+  ret i32 291, !dbg !11
+}
+
+; Function Attrs: inaccessiblemem_or_argmemonly nounwind
+declare void @llvm.prefetch(i8* nocapture readonly, i32, i32, i32) #1
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.x86.avx512.gatherpf.dpd.512(i8, <8 x i32>, i8*, i32, i32) #2
+
+attributes #0 = {"target-cpu"="x86-64" "target-features"="+avx512pf,+sse4.2,+ssse3"}
+attributes #1 = { inaccessiblemem_or_argmemonly nounwind }
+attributes #2 = { argmemonly nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, debugInfoForProfiling: true)
+!1 = !DIFile(filename: "prefetch.cc", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 7.0.0 (trunk 327078) (llvm/trunk 327086)"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 12, column: 3, scope: !7)
+!10 = !DILocation(line: 14, column: 3, scope: !7)
+!11 = !DILocation(line: 15, column: 3, scope: !7)
+
+;CHECK-LABEL: main:
+;CHECK:       # %bb.0:
+;CHECK:       prefetchnta 291
+;CHECK-NOT:   prefetchnta 42(%rax,%ymm0)
+;CHECK:       vgatherpf1dpd (%rax,%ymm0) {%k1}
Index: llvm/trunk/test/CodeGen/X86/insert-prefetch-no-MachineMemOperand.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/insert-prefetch-no-MachineMemOperand.ll
+++ llvm/trunk/test/CodeGen/X86/insert-prefetch-no-MachineMemOperand.ll
@@ -1,46 +0,0 @@
-; RUN: llc < %s -prefetch-hints-file=%S/insert-prefetch-nomemop.afdo | FileCheck %s
-; ModuleID = 'prefetch.cc'
-source_filename = "prefetch.cc"
-target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
-target triple = "x86_64-unknown-linux-gnu"
-
-; Function Attrs: norecurse nounwind uwtable
-define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
-entry:
-  tail call void @llvm.prefetch(i8* inttoptr (i64 291 to i8*), i32 0, i32 0, i32 1), !dbg !9
-  tail call void @llvm.x86.avx512.gatherpf.dpd.512(i8 97, <8 x i32> undef, i8* null, i32 1, i32 2), !dbg !10
-  ret i32 291, !dbg !11
-}
-
-; Function Attrs: inaccessiblemem_or_argmemonly nounwind
-declare void @llvm.prefetch(i8* nocapture readonly, i32, i32, i32) #1
-
-; Function Attrs: argmemonly nounwind
-declare void @llvm.x86.avx512.gatherpf.dpd.512(i8, <8 x i32>, i8*, i32, i32) #2
-
-attributes #0 = {"target-cpu"="x86-64" "target-features"="+avx512pf,+sse4.2,+ssse3"}
-attributes #1 = { inaccessiblemem_or_argmemonly nounwind }
-attributes #2 = { argmemonly nounwind }
-
-!llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!3, !4, !5}
-!llvm.ident = !{!6}
-
-!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, debugInfoForProfiling: true)
-!1 = !DIFile(filename: "prefetch.cc", directory: "/tmp")
-!2 = !{}
-!3 = !{i32 2, !"Dwarf Version", i32 4}
-!4 = !{i32 2, !"Debug Info Version", i32 3}
-!5 = !{i32 1, !"wchar_size", i32 4}
-!6 = !{!"clang version 7.0.0 (trunk 327078) (llvm/trunk 327086)"}
-!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
-!8 = !DISubroutineType(types: !2)
-!9 = !DILocation(line: 12, column: 3, scope: !7)
-!10 = !DILocation(line: 14, column: 3, scope: !7)
-!11 = !DILocation(line: 15, column: 3, scope: !7)
-
-;CHECK-LABEL: main:
-;CHECK:       # %bb.0:
-;CHECK:       prefetchnta 291
-;CHECK:       prefetchnta 42(%rax,%ymm0)
-;CHECK-NEXT:  vgatherpf1dpd (%rax,%ymm0) {%k1}
Index: llvm/trunk/test/CodeGen/X86/insert-prefetch-nomemop.afdo
===================================================================
--- llvm/trunk/test/CodeGen/X86/insert-prefetch-nomemop.afdo
+++ llvm/trunk/test/CodeGen/X86/insert-prefetch-nomemop.afdo
@@ -1,2 +0,0 @@
-main:0:0
- 6: 0 __prefetch_nta_0:42
\ No newline at end of file