[llvm] [SystemZ][z/OS] Add a parameter Align to emitIncrement() and use 32 for XPLINK stack on z/OS. (PR #182348)

[via llvm-commits]

https://github.com/sujianIBM created https://github.com/llvm/llvm-project/pull/182348

The stack alignment for 64-bit XPLINK is 32 on z/OS, but not 8.
This PR fixes this and adds a test to verify it.

>From 08d439fead327547f65a73285ed39320533ac12d Mon Sep 17 00:00:00 2001
From: Jian Su <jian.su at ibm.com>
Date: Thu, 22 Jan 2026 15:24:40 +0000
Subject: [PATCH] Add a parameter Align to emitIncrement() and use 32 for
 XPLINK on z/OS.

---
 llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp | 10 +++++-----
 llvm/test/CodeGen/SystemZ/zos-prologue-epilog.ll | 13 ++++++++++++-
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index d4c8f61245ae1..a11af9f2ef5ae 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -478,7 +478,7 @@ void SystemZELFFrameLowering::processFunctionBeforeFrameFinalized(
 static void emitIncrement(MachineBasicBlock &MBB,
                           MachineBasicBlock::iterator &MBBI, const DebugLoc &DL,
                           Register Reg, int64_t NumBytes,
-                          const TargetInstrInfo *TII) {
+                          const TargetInstrInfo *TII, unsigned Align = 8) {
   while (NumBytes) {
     unsigned Opcode;
     int64_t ThisVal = NumBytes;
@@ -486,9 +486,9 @@ static void emitIncrement(MachineBasicBlock &MBB,
       Opcode = SystemZ::AGHI;
     else {
       Opcode = SystemZ::AGFI;
-      // Make sure we maintain 8-byte stack alignment.
+      // Make sure we maintain Align-byte stack alignment.
       int64_t MinVal = -uint64_t(1) << 31;
-      int64_t MaxVal = (int64_t(1) << 31) - 8;
+      int64_t MaxVal = (int64_t(1) << 31) - Align;
       if (ThisVal < MinVal)
         ThisVal = MinVal;
       else if (ThisVal > MaxVal)
@@ -1299,7 +1299,7 @@ void SystemZXPLINKFrameLowering::emitPrologue(MachineFunction &MF,
     }
 
     emitIncrement(MBB, InsertPt, DL, Regs.getStackPointerRegister(), Delta,
-                  ZII);
+                  ZII, /* Align = */32);
 
     // If the requested stack size is larger than the guard page, then we need
     // to check if we need to call the stack extender. This requires adding a
@@ -1369,7 +1369,7 @@ void SystemZXPLINKFrameLowering::emitEpilogue(MachineFunction &MF,
     unsigned SPReg = Regs.getStackPointerRegister();
     if (ZFI->getRestoreGPRRegs().LowGPR != SPReg) {
       DebugLoc DL = MBBI->getDebugLoc();
-      emitIncrement(MBB, MBBI, DL, SPReg, StackSize, ZII);
+      emitIncrement(MBB, MBBI, DL, SPReg, StackSize, ZII, /* Align = */32);
     }
   }
 }
diff --git a/llvm/test/CodeGen/SystemZ/zos-prologue-epilog.ll b/llvm/test/CodeGen/SystemZ/zos-prologue-epilog.ll
index ecf778a36755b..8b00490db47e6 100644
--- a/llvm/test/CodeGen/SystemZ/zos-prologue-epilog.ll
+++ b/llvm/test/CodeGen/SystemZ/zos-prologue-epilog.ll
@@ -376,7 +376,6 @@ define void @large_stack1(i64 %n1, i64 %n2, i64 %n3) {
   ret void
 }
 
-
 ; CHECK-LABEL: large_stack2
 ; CHECK64: lgr 0,4
 ; CHECK64: stg 3,2192(4)
@@ -400,6 +399,18 @@ define void @large_stack2(i64 %n1, i64 %n2, i64 %n3) {
   ret void
 }
 
+; Verify stack alignment is 32
+; CHECK-LABEL: large_stack3
+; CHECK: agfi 4,-2147483648
+; CHECK-NEXT: aghi 4,-224
+; CHECK: agfi 4,2147483616
+; CHECK-NEXT: aghi 4,256
+define void @large_stack3() {
+  %arr = alloca [268435457 x i64], align 8
+  call i64 (ptr) @fun1(ptr %arr)
+  ret void
+}
+
 ; CHECK-LABEL: L#EPM_leaf_func0_0 DS 0H
 ; CHECK: * DSA Size 0x0
 ; CHECK: * Entry Flags