From f309f095e7c677aa23866865e8d25fe501dd7d02 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
Date: Fri, 14 Oct 2022 11:27:39 +0300
Subject: [PATCH] Revert "[AArch64] Fix aligning the stack after calling
 __chkstk"

This reverts commit 50e0aced4521260af842dba73f1d8c50d36314ea.

This could accidentally start producing invalid code in some
cases (in particular, if compiling with -mstack-alignment=16, which
one could expect to be a no-op for a target where the stack always
is aligned to 16 bytes anyway).
---
 llvm/lib/Target/AArch64/AArch64FrameLowering.cpp | 34 +++++-------------------
 llvm/test/CodeGen/AArch64/win-align-chkstk.ll    | 27 -------------------
 2 files changed, 6 insertions(+), 55 deletions(-)
 delete mode 100644 llvm/test/CodeGen/AArch64/win-align-chkstk.ll

diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 336bbb0..4939a22 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -1496,15 +1496,7 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   // function, including the funclet.
   int64_t NumBytes = IsFunclet ? getWinEHFuncletFrameSize(MF)
                                : MFI.getStackSize();
-
-  // Alignment is required for the parent frame, not the funclet
-  const bool NeedsRealignment =
-      NumBytes && !IsFunclet && RegInfo->hasStackRealignment(MF);
-  int64_t RealignmentPadding =
-      NeedsRealignment ? MFI.getMaxAlign().value() - 16 : 0;
-
-  if (!AFI->hasStackFrame() &&
-      !windowsRequiresStackProbe(MF, NumBytes + RealignmentPadding)) {
+  if (!AFI->hasStackFrame() && !windowsRequiresStackProbe(MF, NumBytes)) {
     assert(!HasFP && "unexpected function without stack frame but with FP");
     assert(!SVEStackSize &&
            "unexpected function without stack frame but with SVE objects");
@@ -1646,8 +1638,8 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   if (EmitCFI)
     emitCalleeSavedGPRLocations(MBB, MBBI);
 
-  if (windowsRequiresStackProbe(MF, NumBytes + RealignmentPadding)) {
-    uint64_t NumWords = (NumBytes + RealignmentPadding) >> 4;
+  if (windowsRequiresStackProbe(MF, NumBytes)) {
+    uint64_t NumWords = NumBytes >> 4;
     if (NeedsWinCFI) {
       HasWinCFI = true;
       // alloc_l can hold at most 256MB, so assume that NumBytes doesn't
@@ -1739,23 +1731,6 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
           .setMIFlag(MachineInstr::FrameSetup);
     }
     NumBytes = 0;
-
-    if (NeedsRealignment) {
-      BuildMI(MBB, MBBI, DL, TII->get(AArch64::ADDXri), AArch64::X15)
-          .addReg(AArch64::SP)
-          .addImm(RealignmentPadding)
-          .addImm(0);
-
-      uint64_t AndMask = ~(MFI.getMaxAlign().value() - 1);
-      BuildMI(MBB, MBBI, DL, TII->get(AArch64::ANDXri), AArch64::SP)
-          .addReg(AArch64::X15, RegState::Kill)
-          .addImm(AArch64_AM::encodeLogicalImmediate(AndMask, 64));
-      AFI->setStackRealigned(true);
-
-      // No need for SEH instructions here; if we're realigning the stack,
-      // we've set a frame pointer and already finished the SEH prologue.
-      assert(!NeedsWinCFI);
-    }
   }
 
   StackOffset AllocateBefore = SVEStackSize, AllocateAfter = {};
@@ -1794,6 +1769,9 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
 
   // Allocate space for the rest of the frame.
   if (NumBytes) {
+    // Alignment is required for the parent frame, not the funclet
+    const bool NeedsRealignment =
+        !IsFunclet && RegInfo->hasStackRealignment(MF);
     unsigned scratchSPReg = AArch64::SP;
 
     if (NeedsRealignment) {
diff --git a/llvm/test/CodeGen/AArch64/win-align-chkstk.ll b/llvm/test/CodeGen/AArch64/win-align-chkstk.ll
deleted file mode 100644
index 7c1c3db..0000000
--- a/llvm/test/CodeGen/AArch64/win-align-chkstk.ll
+++ /dev/null
@@ -1,27 +0,0 @@
-; RUN: llc < %s -mtriple=aarch64-windows | FileCheck %s
-
-define dso_local void @func() {
-entry:
-  %buf = alloca [8192 x i8], align 32
-  %arraydecay = getelementptr inbounds [8192 x i8], ptr %buf, i64 0, i64 0
-  call void @other(ptr noundef %arraydecay)
-  ret void
-}
-
-declare dso_local void @other(ptr noundef)
-
-; CHECK-LABEL: func:
-; CHECK-NEXT: .seh_proc func
-; CHECK-NEXT: // %bb.0:
-; CHECK-NEXT: str x28, [sp, #-32]!
-; CHECK-NEXT: .seh_save_reg_x x28, 32
-; CHECK-NEXT: stp x29, x30, [sp, #8]
-; CHECK-NEXT: .seh_save_fplr 8
-; CHECK-NEXT: add x29, sp, #8
-; CHECK-NEXT: .seh_add_fp 8
-; CHECK-NEXT: .seh_endprologue
-; CHECK-NEXT: mov x15, #513
-; CHECK-NEXT: bl __chkstk
-; CHECK-NEXT: sub sp, sp, x15, lsl #4
-; CHECK-NEXT: add x15, sp, #16
-; CHECK-NEXT: and sp, x15, #0xffffffffffffffe0
-- 
2.7.4