diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 4dc2ff481785db..bac8838a0adcc7 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3808,7 +3808,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
                          "the only memory argument");
   }
 
-  if (!IsSibcall)
+  if (!IsSibcall && !IsMustTail)
     Chain = DAG.getCALLSEQ_START(Chain, NumBytesToPush,
                                  NumBytes - NumBytesToPush, dl);
 
@@ -4093,7 +4093,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
   SmallVector<SDValue, 8> Ops;
 
-  if (!IsSibcall && isTailCall) {
+  if (!IsSibcall && isTailCall && !IsMustTail) {
     Chain = DAG.getCALLSEQ_END(Chain,
                                DAG.getIntPtrConstant(NumBytesToPop, dl, true),
                                DAG.getIntPtrConstant(0, dl, true), InFlag, dl);
diff --git a/llvm/test/CodeGen/X86/cfguard-checks.ll b/llvm/test/CodeGen/X86/cfguard-checks.ll
index efd6e7bc11b63c..6e8d71411e8267 100644
--- a/llvm/test/CodeGen/X86/cfguard-checks.ll
+++ b/llvm/test/CodeGen/X86/cfguard-checks.ll
@@ -171,8 +171,7 @@ entry:
 
   ; X64-LABEL: func_cf_tail
   ; X64:       leaq	target_func(%rip), %rax
-  ; X64:       movq __guard_dispatch_icall_fptr(%rip), %rcx
-  ; X64:       rex64 jmpq *%rcx            # TAILCALL
+  ; X64:       rex64 jmpq *__guard_dispatch_icall_fptr(%rip)         # TAILCALL
   ; X64-NOT:   callq
 }
 
@@ -205,7 +204,6 @@ entry:
   ; X64:            movq (%rcx), %rax
   ; X64-NEXT:       movq 8(%rax), %rax
   ; X64-NEXT:       movq __guard_dispatch_icall_fptr(%rip), %rdx
-  ; X64-NEXT:       addq $40, %rsp
   ; X64-NEXT:       rex64 jmpq *%rdx            # TAILCALL
   ; X64-NOT:   callq
 }
diff --git a/llvm/test/CodeGen/X86/musttail-inalloca.ll b/llvm/test/CodeGen/X86/musttail-inalloca.ll
new file mode 100644
index 00000000000000..c17d29c4c71d3f
--- /dev/null
+++ b/llvm/test/CodeGen/X86/musttail-inalloca.ll
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc %s -o - | FileCheck %s
+
+; Previously, we would accidentally leave behind SP adjustments to setup a call
+; frame for the musttail call target, and SP adjustments would end up
+; unbalanced. Reported as https://crbug.com/1026882.
+
+target datalayout = "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i386-pc-windows-msvc19.16.0"
+
+; 20 bytes of memory.
+%struct.Args = type { i32, i32, i32, i32, i32 }
+
+declare dso_local x86_thiscallcc void @methodWithVtorDisp(i8* nocapture readonly, <{ %struct.Args }>* inalloca)
+
+define dso_local x86_thiscallcc void @methodWithVtorDisp_thunk(i8* %0, <{ %struct.Args }>* inalloca %1) #0 {
+; CHECK-LABEL: methodWithVtorDisp_thunk:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushl %esi
+; CHECK-NEXT:    movl %ecx, %esi
+; CHECK-NEXT:    subl -4(%ecx), %esi
+; CHECK-NEXT:    pushl {{[0-9]+}}(%esp)
+; CHECK-NEXT:    pushl $_methodWithVtorDisp_thunk
+; CHECK-NEXT:    calll ___cyg_profile_func_exit
+; CHECK-NEXT:    addl $8, %esp
+; CHECK-NEXT:    movl %esi, %ecx
+; CHECK-NEXT:    popl %esi
+; CHECK-NEXT:    jmp _methodWithVtorDisp # TAILCALL
+  %3 = getelementptr inbounds i8, i8* %0, i32 -4
+  %4 = bitcast i8* %3 to i32*
+  %5 = load i32, i32* %4, align 4
+  %6 = sub i32 0, %5
+  %7 = getelementptr i8, i8* %0, i32 %6
+  musttail call x86_thiscallcc void @methodWithVtorDisp(i8* %7, <{ %struct.Args }>* inalloca nonnull %1)
+  ret void
+}
+
+attributes #0 = { nounwind optsize "instrument-function-exit-inlined"="__cyg_profile_func_exit"  }
diff --git a/llvm/test/CodeGen/X86/musttail-tailcc.ll b/llvm/test/CodeGen/X86/musttail-tailcc.ll
index 6057045a77dfa9..4de8d4e2be1289 100644
--- a/llvm/test/CodeGen/X86/musttail-tailcc.ll
+++ b/llvm/test/CodeGen/X86/musttail-tailcc.ll
@@ -9,8 +9,6 @@ declare tailcc i32 @tailcallee(i32 %a1, i32 %a2)
 define tailcc i32 @tailcaller(i32 %in1, i32 %in2) nounwind {
 ; X64-LABEL: tailcaller:
 ; X64:       # %bb.0: # %entry
-; X64-NEXT:    pushq %rax
-; X64-NEXT:    popq %rax
 ; X64-NEXT:    jmp tailcallee # TAILCALL
 ;
 ; X32-LABEL: tailcaller:
@@ -26,8 +24,6 @@ declare tailcc i8* @alias_callee()
 define tailcc noalias i8* @noalias_caller() nounwind {
 ; X64-LABEL: noalias_caller:
 ; X64:       # %bb.0:
-; X64-NEXT:    pushq %rax
-; X64-NEXT:    popq %rax
 ; X64-NEXT:    jmp alias_callee # TAILCALL
 ;
 ; X32-LABEL: noalias_caller:
@@ -42,8 +38,6 @@ declare tailcc noalias i8* @noalias_callee()
 define tailcc i8* @alias_caller() nounwind {
 ; X64-LABEL: alias_caller:
 ; X64:       # %bb.0:
-; X64-NEXT:    pushq %rax
-; X64-NEXT:    popq %rax
 ; X64-NEXT:    jmp noalias_callee # TAILCALL
 ;
 ; X32-LABEL: alias_caller:
@@ -56,25 +50,17 @@ define tailcc i8* @alias_caller() nounwind {
 define tailcc void @void_test(i32, i32, i32, i32) {
 ; X64-LABEL: void_test:
 ; X64:       # %bb.0: # %entry
-; X64-NEXT:    pushq %rax
-; X64-NEXT:    .cfi_def_cfa_offset 16
-; X64-NEXT:    popq %rax
-; X64-NEXT:    .cfi_def_cfa_offset 8
 ; X64-NEXT:    jmp void_test # TAILCALL
 ;
 ; X32-LABEL: void_test:
 ; X32:       # %bb.0: # %entry
 ; X32-NEXT:    pushl %esi
 ; X32-NEXT:    .cfi_def_cfa_offset 8
-; X32-NEXT:    subl $8, %esp
-; X32-NEXT:    .cfi_def_cfa_offset 16
 ; X32-NEXT:    .cfi_offset %esi, -8
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %esi
 ; X32-NEXT:    movl %esi, {{[0-9]+}}(%esp)
 ; X32-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X32-NEXT:    addl $8, %esp
-; X32-NEXT:    .cfi_def_cfa_offset 8
 ; X32-NEXT:    popl %esi
 ; X32-NEXT:    .cfi_def_cfa_offset 4
 ; X32-NEXT:    jmp void_test # TAILCALL
@@ -86,25 +72,17 @@ define tailcc void @void_test(i32, i32, i32, i32) {
 define tailcc i1 @i1test(i32, i32, i32, i32) {
 ; X64-LABEL: i1test:
 ; X64:       # %bb.0: # %entry
-; X64-NEXT:    pushq %rax
-; X64-NEXT:    .cfi_def_cfa_offset 16
-; X64-NEXT:    popq %rax
-; X64-NEXT:    .cfi_def_cfa_offset 8
 ; X64-NEXT:    jmp i1test # TAILCALL
 ;
 ; X32-LABEL: i1test:
 ; X32:       # %bb.0: # %entry
 ; X32-NEXT:    pushl %esi
 ; X32-NEXT:    .cfi_def_cfa_offset 8
-; X32-NEXT:    subl $8, %esp
-; X32-NEXT:    .cfi_def_cfa_offset 16
 ; X32-NEXT:    .cfi_offset %esi, -8
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %esi
 ; X32-NEXT:    movl %esi, {{[0-9]+}}(%esp)
 ; X32-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X32-NEXT:    addl $8, %esp
-; X32-NEXT:    .cfi_def_cfa_offset 8
 ; X32-NEXT:    popl %esi
 ; X32-NEXT:    .cfi_def_cfa_offset 4
 ; X32-NEXT:    jmp i1test # TAILCALL
diff --git a/llvm/test/CodeGen/X86/musttail-varargs.ll b/llvm/test/CodeGen/X86/musttail-varargs.ll
index 5f5ce5f9af9135..5d88f0dd11cd63 100644
--- a/llvm/test/CodeGen/X86/musttail-varargs.ll
+++ b/llvm/test/CodeGen/X86/musttail-varargs.ll
@@ -246,12 +246,13 @@ define void @f_thunk(i8* %this, ...) {
 ; X86-NOSSE-NEXT:    movl %esp, %ebp
 ; X86-NOSSE-NEXT:    pushl %esi
 ; X86-NOSSE-NEXT:    andl $-16, %esp
-; X86-NOSSE-NEXT:    subl $48, %esp
+; X86-NOSSE-NEXT:    subl $32, %esp
 ; X86-NOSSE-NEXT:    movl 8(%ebp), %esi
 ; X86-NOSSE-NEXT:    leal 12(%ebp), %eax
-; X86-NOSSE-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X86-NOSSE-NEXT:    movl %esi, (%esp)
+; X86-NOSSE-NEXT:    movl %eax, (%esp)
+; X86-NOSSE-NEXT:    pushl %esi
 ; X86-NOSSE-NEXT:    calll _get_f
+; X86-NOSSE-NEXT:    addl $4, %esp
 ; X86-NOSSE-NEXT:    movl %esi, 8(%ebp)
 ; X86-NOSSE-NEXT:    leal -4(%ebp), %esp
 ; X86-NOSSE-NEXT:    popl %esi
@@ -264,17 +265,18 @@ define void @f_thunk(i8* %this, ...) {
 ; X86-SSE-NEXT:    movl %esp, %ebp
 ; X86-SSE-NEXT:    pushl %esi
 ; X86-SSE-NEXT:    andl $-16, %esp
-; X86-SSE-NEXT:    subl $96, %esp
+; X86-SSE-NEXT:    subl $80, %esp
 ; X86-SSE-NEXT:    movaps %xmm2, {{[-0-9]+}}(%e{{[sb]}}p) # 16-byte Spill
 ; X86-SSE-NEXT:    movaps %xmm1, {{[-0-9]+}}(%e{{[sb]}}p) # 16-byte Spill
-; X86-SSE-NEXT:    movaps %xmm0, {{[-0-9]+}}(%e{{[sb]}}p) # 16-byte Spill
+; X86-SSE-NEXT:    movaps %xmm0, (%esp) # 16-byte Spill
 ; X86-SSE-NEXT:    movl 8(%ebp), %esi
 ; X86-SSE-NEXT:    leal 12(%ebp), %eax
 ; X86-SSE-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X86-SSE-NEXT:    movl %esi, (%esp)
+; X86-SSE-NEXT:    pushl %esi
 ; X86-SSE-NEXT:    calll _get_f
+; X86-SSE-NEXT:    addl $4, %esp
 ; X86-SSE-NEXT:    movl %esi, 8(%ebp)
-; X86-SSE-NEXT:    movaps {{[-0-9]+}}(%e{{[sb]}}p), %xmm0 # 16-byte Reload
+; X86-SSE-NEXT:    movaps (%esp), %xmm0 # 16-byte Reload
 ; X86-SSE-NEXT:    movaps {{[-0-9]+}}(%e{{[sb]}}p), %xmm1 # 16-byte Reload
 ; X86-SSE-NEXT:    movaps {{[-0-9]+}}(%e{{[sb]}}p), %xmm2 # 16-byte Reload
 ; X86-SSE-NEXT:    leal -4(%ebp), %esp
@@ -300,38 +302,21 @@ define void @f_thunk(i8* %this, ...) {
 define void @g_thunk(i8* %fptr_i8, ...) {
 ; LINUX-LABEL: g_thunk:
 ; LINUX:       # %bb.0:
-; LINUX-NEXT:    pushq %rax
-; LINUX-NEXT:    .cfi_def_cfa_offset 16
-; LINUX-NEXT:    popq %r11
-; LINUX-NEXT:    .cfi_def_cfa_offset 8
 ; LINUX-NEXT:    jmpq *%rdi # TAILCALL
 ;
 ; LINUX-X32-LABEL: g_thunk:
 ; LINUX-X32:       # %bb.0:
-; LINUX-X32-NEXT:    pushq %rax
-; LINUX-X32-NEXT:    .cfi_def_cfa_offset 16
 ; LINUX-X32-NEXT:    movl %edi, %r11d
-; LINUX-X32-NEXT:    addl $8, %esp
-; LINUX-X32-NEXT:    .cfi_def_cfa_offset 8
 ; LINUX-X32-NEXT:    jmpq *%r11 # TAILCALL
 ;
 ; WINDOWS-LABEL: g_thunk:
 ; WINDOWS:       # %bb.0:
-; WINDOWS-NEXT:    subq $40, %rsp
-; WINDOWS-NEXT:    .seh_stackalloc 40
-; WINDOWS-NEXT:    .seh_endprologue
-; WINDOWS-NEXT:    addq $40, %rsp
 ; WINDOWS-NEXT:    rex64 jmpq *%rcx # TAILCALL
-; WINDOWS-NEXT:    .seh_handlerdata
-; WINDOWS-NEXT:    .text
-; WINDOWS-NEXT:    .seh_endproc
 ;
 ; X86-LABEL: g_thunk:
 ; X86:       # %bb.0:
-; X86-NEXT:    pushl %eax
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X86-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X86-NEXT:    popl %ecx
 ; X86-NEXT:    jmpl *%eax # TAILCALL
   %fptr = bitcast i8* %fptr_i8 to void (i8*, ...)*
   musttail call void (i8*, ...) %fptr(i8* %fptr_i8, ...)
@@ -347,78 +332,53 @@ define void @g_thunk(i8* %fptr_i8, ...) {
 define void @h_thunk(%struct.Foo* %this, ...) {
 ; LINUX-LABEL: h_thunk:
 ; LINUX:       # %bb.0:
-; LINUX-NEXT:    pushq %rax
-; LINUX-NEXT:    .cfi_def_cfa_offset 16
 ; LINUX-NEXT:    cmpb $1, (%rdi)
 ; LINUX-NEXT:    jne .LBB2_2
 ; LINUX-NEXT:  # %bb.1: # %then
 ; LINUX-NEXT:    movq 8(%rdi), %r11
-; LINUX-NEXT:    addq $8, %rsp
-; LINUX-NEXT:    .cfi_def_cfa_offset 8
 ; LINUX-NEXT:    jmpq *%r11 # TAILCALL
 ; LINUX-NEXT:  .LBB2_2: # %else
-; LINUX-NEXT:    .cfi_def_cfa_offset 16
 ; LINUX-NEXT:    movq 16(%rdi), %r11
 ; LINUX-NEXT:    movl $42, {{.*}}(%rip)
-; LINUX-NEXT:    addq $8, %rsp
-; LINUX-NEXT:    .cfi_def_cfa_offset 8
 ; LINUX-NEXT:    jmpq *%r11 # TAILCALL
 ;
 ; LINUX-X32-LABEL: h_thunk:
 ; LINUX-X32:       # %bb.0:
-; LINUX-X32-NEXT:    pushq %rax
-; LINUX-X32-NEXT:    .cfi_def_cfa_offset 16
 ; LINUX-X32-NEXT:    cmpb $1, (%edi)
 ; LINUX-X32-NEXT:    jne .LBB2_2
 ; LINUX-X32-NEXT:  # %bb.1: # %then
 ; LINUX-X32-NEXT:    movl 4(%edi), %r11d
-; LINUX-X32-NEXT:    addl $8, %esp
-; LINUX-X32-NEXT:    .cfi_def_cfa_offset 8
 ; LINUX-X32-NEXT:    jmpq *%r11 # TAILCALL
 ; LINUX-X32-NEXT:  .LBB2_2: # %else
-; LINUX-X32-NEXT:    .cfi_def_cfa_offset 16
 ; LINUX-X32-NEXT:    movl 8(%edi), %r11d
 ; LINUX-X32-NEXT:    movl $42, {{.*}}(%rip)
-; LINUX-X32-NEXT:    addl $8, %esp
-; LINUX-X32-NEXT:    .cfi_def_cfa_offset 8
 ; LINUX-X32-NEXT:    jmpq *%r11 # TAILCALL
 ;
 ; WINDOWS-LABEL: h_thunk:
 ; WINDOWS:       # %bb.0:
-; WINDOWS-NEXT:    subq $40, %rsp
-; WINDOWS-NEXT:    .seh_stackalloc 40
-; WINDOWS-NEXT:    .seh_endprologue
 ; WINDOWS-NEXT:    cmpb $1, (%rcx)
 ; WINDOWS-NEXT:    jne .LBB2_2
 ; WINDOWS-NEXT:  # %bb.1: # %then
 ; WINDOWS-NEXT:    movq 8(%rcx), %rax
-; WINDOWS-NEXT:    addq $40, %rsp
 ; WINDOWS-NEXT:    rex64 jmpq *%rax # TAILCALL
 ; WINDOWS-NEXT:  .LBB2_2: # %else
 ; WINDOWS-NEXT:    movq 16(%rcx), %rax
 ; WINDOWS-NEXT:    movl $42, {{.*}}(%rip)
-; WINDOWS-NEXT:    addq $40, %rsp
 ; WINDOWS-NEXT:    rex64 jmpq *%rax # TAILCALL
-; WINDOWS-NEXT:    .seh_handlerdata
-; WINDOWS-NEXT:    .text
-; WINDOWS-NEXT:    .seh_endproc
 ;
 ; X86-LABEL: h_thunk:
 ; X86:       # %bb.0:
-; X86-NEXT:    pushl %eax
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X86-NEXT:    cmpb $1, (%eax)
 ; X86-NEXT:    jne LBB2_2
 ; X86-NEXT:  # %bb.1: # %then
 ; X86-NEXT:    movl 4(%eax), %ecx
 ; X86-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X86-NEXT:    popl %eax
 ; X86-NEXT:    jmpl *%ecx # TAILCALL
 ; X86-NEXT:  LBB2_2: # %else
 ; X86-NEXT:    movl 8(%eax), %ecx
 ; X86-NEXT:    movl $42, _g
 ; X86-NEXT:    movl %eax, {{[0-9]+}}(%esp)
-; X86-NEXT:    popl %eax
 ; X86-NEXT:    jmpl *%ecx # TAILCALL
   %cond_p = getelementptr %struct.Foo, %struct.Foo* %this, i32 0, i32 0
   %cond = load i1, i1* %cond_p