Index: lib/Target/X86/X86TargetTransformInfo.h
===================================================================
--- lib/Target/X86/X86TargetTransformInfo.h
+++ lib/Target/X86/X86TargetTransformInfo.h
@@ -189,6 +189,9 @@
   bool isFCmpOrdCheaperThanFCmpZero(Type *Ty);
   bool areInlineCompatible(const Function *Caller,
                            const Function *Callee) const;
+  bool areFunctionArgsABICompatible(const Function *Caller,
+                                    const Function *Callee,
+                                    SmallPtrSetImpl<Argument *> &Args) const;
   const TTI::MemCmpExpansionOptions *enableMemCmpExpansion(
       bool IsZeroCmp) const;
   bool enableInterleavedAccessVectorization();
Index: lib/Target/X86/X86TargetTransformInfo.cpp
===================================================================
--- lib/Target/X86/X86TargetTransformInfo.cpp
+++ lib/Target/X86/X86TargetTransformInfo.cpp
@@ -3070,6 +3070,22 @@
   return (RealCallerBits & RealCalleeBits) == RealCalleeBits;
 }
 
+bool X86TTIImpl::areFunctionArgsABICompatible(
+    const Function *Caller, const Function *Callee,
+    SmallPtrSetImpl<Argument *> &Args) const {
+  if (!BaseT::areFunctionArgsABICompatible(Caller, Callee, Args))
+    return false;
+
+  // If we get here, we know the target features match. If one function
+  // considers 512-bit vectors legal and the other does not, consider them
+  // incompatible.
+  // FIXME Look at the arguments and only consider 512 bit or larger vectors?
+  const TargetMachine &TM = getTLI()->getTargetMachine();
+
+  return TM.getSubtarget<X86Subtarget>(*Caller).useAVX512Regs() ==
+         TM.getSubtarget<X86Subtarget>(*Callee).useAVX512Regs();
+}
+
 const X86TTIImpl::TTI::MemCmpExpansionOptions *
 X86TTIImpl::enableMemCmpExpansion(bool IsZeroCmp) const {
   // Only enable vector loads for equality comparison.
Index: test/Transforms/ArgumentPromotion/X86/min-legal-vector-width.ll
===================================================================
--- /dev/null
+++ test/Transforms/ArgumentPromotion/X86/min-legal-vector-width.ll
@@ -0,0 +1,184 @@
+; RUN: opt -S -argpromotion < %s | FileCheck %s
+; RUN: opt -S -passes=argpromotion < %s | FileCheck %s
+; Test that we only promote arguments when the caller/callee have compatible
+; function attrubtes.
+
+target triple = "x86_64-unknown-linux-gnu"
+
+; This should promote
+; CHECK-LABEL: @callee_avx512_legal512_prefer512_call_avx512_legal512_prefer512(<8 x i64>* %arg, <8 x i64> %arg1.val)
+define internal fastcc void @callee_avx512_legal512_prefer512_call_avx512_legal512_prefer512(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #0 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx512_legal512_prefer512_call_avx512_legal512_prefer512(<8 x i64>* %arg) #0 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx512_legal512_prefer512_call_avx512_legal512_prefer512(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should promote
+; CHECK-LABEL: @callee_avx512_legal512_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %arg, <8 x i64> %arg1.val)
+define internal fastcc void @callee_avx512_legal512_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #1 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx512_legal512_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %arg) #1 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx512_legal512_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should promote
+; CHECK-LABEL: @callee_avx512_legal512_prefer512_call_avx512_legal512_prefer256(<8 x i64>* %arg, <8 x i64> %arg1.val)
+define internal fastcc void @callee_avx512_legal512_prefer512_call_avx512_legal512_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #1 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx512_legal512_prefer512_call_avx512_legal512_prefer256(<8 x i64>* %arg) #0 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx512_legal512_prefer512_call_avx512_legal512_prefer256(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should promote
+; CHECK-LABEL: @callee_avx512_legal512_prefer256_call_avx512_legal512_prefer512(<8 x i64>* %arg, <8 x i64> %arg1.val)
+define internal fastcc void @callee_avx512_legal512_prefer256_call_avx512_legal512_prefer512(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #0 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx512_legal512_prefer256_call_avx512_legal512_prefer512(<8 x i64>* %arg) #1 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx512_legal512_prefer256_call_avx512_legal512_prefer512(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should not promote
+; CHECK-LABEL: @callee_avx512_legal256_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1)
+define internal fastcc void @callee_avx512_legal256_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #1 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx512_legal256_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %arg) #2 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx512_legal256_prefer256_call_avx512_legal512_prefer256(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should not promote
+; CHECK-LABEL: @callee_avx512_legal512_prefer256_call_avx512_legal256_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1)
+define internal fastcc void @callee_avx512_legal512_prefer256_call_avx512_legal256_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #2 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx512_legal512_prefer256_call_avx512_legal256_prefer256(<8 x i64>* %arg) #1 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx512_legal512_prefer256_call_avx512_legal256_prefer256(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should promote
+; CHECK-LABEL: @callee_avx2_legal256_prefer256_call_avx2_legal512_prefer256(<8 x i64>* %arg, <8 x i64> %arg1.val)
+define internal fastcc void @callee_avx2_legal256_prefer256_call_avx2_legal512_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #3 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx2_legal256_prefer256_call_avx2_legal512_prefer256(<8 x i64>* %arg) #4 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx2_legal256_prefer256_call_avx2_legal512_prefer256(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; This should promote
+; CHECK-LABEL: @callee_avx2_legal512_prefer256_call_avx2_legal256_prefer256(<8 x i64>* %arg, <8 x i64> %arg1.val)
+define internal fastcc void @callee_avx2_legal512_prefer256_call_avx2_legal256_prefer256(<8 x i64>* %arg, <8 x i64>* readonly %arg1) #4 {
+bb:
+  %tmp = load <8 x i64>, <8 x i64>* %arg1
+  store <8 x i64> %tmp, <8 x i64>* %arg
+  ret void
+}
+
+define void @avx2_legal512_prefer256_call_avx2_legal256_prefer256(<8 x i64>* %arg) #3 {
+bb:
+  %tmp = alloca <8 x i64>, align 32
+  %tmp2 = alloca <8 x i64>, align 32
+  %tmp3 = bitcast <8 x i64>* %tmp to i8*
+  call void @llvm.memset.p0i8.i64(i8* align 32 %tmp3, i8 0, i64 32, i1 false)
+  call fastcc void @callee_avx2_legal512_prefer256_call_avx2_legal256_prefer256(<8 x i64>* %tmp2, <8 x i64>* %tmp)
+  %tmp4 = load <8 x i64>, <8 x i64>* %tmp2, align 32
+  store <8 x i64> %tmp4, <8 x i64>* %arg, align 2
+  ret void
+}
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1) #5
+
+attributes #0 = { inlinehint norecurse nounwind uwtable "target-features"="+avx512vl" "min-legal-vector-width"="512" "prefer-vector-width"="512" }
+attributes #1 = { inlinehint norecurse nounwind uwtable "target-features"="+avx512vl" "min-legal-vector-width"="512" "prefer-vector-width"="256" }
+attributes #2 = { inlinehint norecurse nounwind uwtable "target-features"="+avx512vl" "min-legal-vector-width"="256" "prefer-vector-width"="256" }
+attributes #3 = { inlinehint norecurse nounwind uwtable "target-features"="+avx2" "min-legal-vector-width"="512" "prefer-vector-width"="256" }
+attributes #4 = { inlinehint norecurse nounwind uwtable "target-features"="+avx2" "min-legal-vector-width"="256" "prefer-vector-width"="256" }
+attributes #5 = { argmemonly nounwind }