[X86][APX] Prevent from emitting push2/pop2 if stack alignment<16B (#143076)

push2/pop2 requires 16-byte stack alignment. If the stack alignment is
less than that, push2/pop2 should not be emitted. It triggers general
protection exception if the data being pushed/popped by push2/pop2 is
not 16-byte aligned on the stack.

Author: fzou1

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -2915,13 +2915,14 @@ bool X86FrameLowering::assignCalleeSavedSpillSlots(
   // 1. Use push2 when
   //       a) number of CSR > 1 if no need padding
   //       b) number of CSR > 2 if need padding
+  //       c) stack alignment >= 16 bytes
   // 2. When the number of CSR push is odd
   //    a. Start to use push2 from the 1st push if stack is 16B aligned.
   //    b. Start to use push2 from the 2nd push if stack is not 16B aligned.
   // 3. When the number of CSR push is even, start to use push2 from the 1st
   //    push and make the stack 16B aligned before the push
   unsigned NumRegsForPush2 = 0;
-  if (STI.hasPush2Pop2()) {
+  if (STI.hasPush2Pop2() && getStackAlignment() >= 16) {
     unsigned NumCSGPR = llvm::count_if(CSI, [](const CalleeSavedInfo &I) {
       return X86::GR64RegClass.contains(I.getReg());
     });

llvm/lib/Target/X86/X86MachineFunctionInfo.h

@@ -149,7 +149,7 @@ class X86MachineFunctionInfo : public MachineFunctionInfo {
   /// other tools to detect the extended record.
   bool HasSwiftAsyncContext = false;
 
-  /// Ajust stack for push2/pop2
+  /// Adjust stack for push2/pop2
   bool PadForPush2Pop2 = false;
 
   /// Candidate registers for push2/pop2

llvm/test/CodeGen/X86/apx/push2-pop2-disabled-with-small-stack-alignment.ll

@@ -0,0 +1,117 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown -mattr=+push2pop2 | FileCheck %s --check-prefix=CHECK
+
+; This test is used to check no push2/pop2 emitted if stack alignment is set to
+; the value less than 16 bytes required by push2/pop2 instruction. Here it's set
+; to 8 bytes.
+
+define void @csr1() nounwind {
+; CHECK-LABEL: csr1:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    retq
+entry:
+  tail call void asm sideeffect "", "~{rbp},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+define void @csr2() nounwind {
+; CHECK-LABEL: csr2:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    retq
+entry:
+  tail call void asm sideeffect "", "~{rbp},~{r15},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+define void @csr3() nounwind {
+; CHECK-LABEL: csr3:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    retq
+entry:
+  tail call void asm sideeffect "", "~{rbp},~{r15},~{r14},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+define void @csr4() nounwind {
+; CHECK-LABEL: csr4:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %r13
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    popq %r13
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    retq
+entry:
+  tail call void asm sideeffect "", "~{rbp},~{r15},~{r14},~{r13},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+define void @csr5() nounwind {
+; CHECK-LABEL: csr5:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %r13
+; CHECK-NEXT:    pushq %r12
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    popq %r12
+; CHECK-NEXT:    popq %r13
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    retq
+entry:
+  tail call void asm sideeffect "", "~{rbp},~{r15},~{r14},~{r13},~{r12},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+define void @csr6() nounwind {
+; CHECK-LABEL: csr6:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %r13
+; CHECK-NEXT:    pushq %r12
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    popq %rbx
+; CHECK-NEXT:    popq %r12
+; CHECK-NEXT:    popq %r13
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    retq
+entry:
+  tail call void asm sideeffect "", "~{rbp},~{r15},~{r14},~{r13},~{r12},~{rbx},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 1, !"override-stack-alignment", i32 8}