[llvm] [SystemZ] Address issue with supper large stack frames on achitecture SystemZ (PR #96318)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-systemz

Author: Zibi Sarbinowski (zibi2)

<details>
<summary>Changes</summary>

This PR fixes the following failure by adjusting the calculation of maximum displacement from Stack Pointer.

`LLVM ERROR: Error while trying to spill R5D from class ADDR64Bit: Cannot scavenge register without an emergency spill slot!
`

---
Full diff: https://github.com/llvm/llvm-project/pull/96318.diff


2 Files Affected:

- (modified) llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp (+22) 
- (added) llvm/test/CodeGen/SystemZ/systemz-large-stack-frames.ll (+42) 


``````````diff
diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index fa20977ec0187..a769fdeff5684 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -1475,6 +1475,28 @@ void SystemZXPLINKFrameLowering::processFunctionBeforeFrameFinalized(
   // with existing compilers.
   MFFrame.setMaxCallFrameSize(
       std::max(64U, (unsigned)alignTo(MFFrame.getMaxCallFrameSize(), 64)));
+
+  // Add frame values with positive object offsets. Since the displacement from
+  // the SP/FP is calculated by ObjectOffset + StackSize + Bias, object offsets
+  // with positive values are in the caller's stack frame. We need to include
+  // that since it is accessed by displacement to SP/FP.
+  int64_t LargestArgOffset = 0;
+  for (int I = MFFrame.getObjectIndexBegin(); I != 0; ++I) {
+    if (MFFrame.getObjectOffset(I) >= 0) {
+      int64_t ObjOffset = MFFrame.getObjectOffset(I) + MFFrame.getObjectSize(I);
+      LargestArgOffset = std::max(ObjOffset, LargestArgOffset);
+    }
+  }
+
+  uint64_t MaxReach = (StackSize + Regs.getCallFrameSize() +
+                       Regs.getStackPointerBias() + LargestArgOffset);
+
+  if (!isUInt<12>(MaxReach)) {
+    // We may need register scavenging slots if some parts of the frame
+    // are outside the reach of an unsigned 12-bit displacement.
+    RS->addScavengingFrameIndex(MFFrame.CreateStackObject(8, Align(8), false));
+    RS->addScavengingFrameIndex(MFFrame.CreateStackObject(8, Align(8), false));
+  }
 }
 
 // Determines the size of the frame, and creates the deferred spill objects.
diff --git a/llvm/test/CodeGen/SystemZ/systemz-large-stack-frames.ll b/llvm/test/CodeGen/SystemZ/systemz-large-stack-frames.ll
new file mode 100644
index 0000000000000..51997a6c17c65
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/systemz-large-stack-frames.ll
@@ -0,0 +1,42 @@
+; REQUIRES: asserts
+; REQUIRES: systemz-registered-target
+; Used to fail with: LLVM ERROR: Error while trying to spill R5D from class ADDR64Bit: Cannot scavenge register without an emergency spill slot!
+
+
+; RUN: llc %s --mtriple s390x-ibm-zos -filetype obj -o %t
+
+; ModuleID = 'main.cpp'
+source_filename = "main.cpp"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; ModuleID = 'large-stack-frames.cpp'
+source_filename = "large-stack-frames.cpp"
+target datalayout = "E-m:l-p1:32:32-i1:8:16-i8:8:16-i64:64-f128:64-v128:64-a:8:16-n32:64"
+target triple = "s390x-ibm-zos"
+%struct.slice.108 = type { ptr, ptr, [8 x i64], [8 x i64], [8 x i64] }
+declare void @dealloc(ptr) local_unnamed_addr #0
+define internal void @foo([26 x i64] %co1, [26 x i64] %co2, [26 x i64] %co3, [26 x i64] %co4, [26 x i64] %co5, [26 x i64] %co6, [26 x i64] %co7, [26 x i64] %co8, i32 %skip_dispatch, ptr %0, i1 %1) #0 {
+entry:
+  %ref.tmp = alloca %struct.slice.108, align 8
+  br i1 %1, label %error, label %if.end95
+if.end95:
+  br i1 %1, label %if.else.i1546, label %object.exit1547
+if.else.i1546:
+  tail call void @dealloc(ptr noundef nonnull %0)
+  br label %object.exit1547
+object.exit1547:
+  %call96 = tail call fastcc noundef ptr @slice([26 x i64] inreg %co7, i32 noundef signext 1, ptr noundef nonnull @get_float, ptr noundef nonnull @object, i32 noundef signext 0)
+  ret void
+error:
+  ret void
+}
+declare dso_local fastcc ptr @slice([26 x i64], i32, ptr, ptr, i32) unnamed_addr #0
+define internal ptr @get_float(ptr %itemp, ptr %2) #0 {
+entry:
+  ret ptr %2
+}
+define internal i32 @object(ptr %itemp, ptr %obj) #0 {
+entry:
+  ret i32 1
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/96318