Add stack layout comment

Change-Id: If04156b0ef35e89a517d8bc06f121d2555ee9379

Author: MacDue

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -56,16 +56,19 @@
 // | async context if needed           |
 // | (a.k.a. "frame record")           |
 // |-----------------------------------| <- fp(=x29)
-// |   <hazard padding>                |
-// |-----------------------------------|
-// |                                   |
-// | callee-saved fp/simd/SVE regs     |
-// |                                   |
-// |-----------------------------------|
-// |                                   |
-// |        SVE stack objects          |
-// |                                   |
-// |-----------------------------------|
+//        Default SVE stack layout                 Split SVE objects
+//   (aarch64-split-sve-objects=false)      (aarch64-split-sve-objects=true)
+// |-----------------------------------|  |-----------------------------------|
+// |         <hazard padding>          |  | callee-saved PPR registers        |
+// |-----------------------------------|  |-----------------------------------|
+// |                                   |  |         PPR stack objects         |
+// | callee-saved fp/simd/SVE regs     |  |-----------------------------------|
+// |                                   |  |         <hazard padding>          |
+// |-----------------------------------|  |-----------------------------------|
+// |                                   |  | callee-saved ZPR registers        |
+// |        SVE stack objects          |  |-----------------------------------|
+// |                                   |  |         ZPR stack objects         |
+// |-----------------------------------|  |-----------------------------------|
 // |.empty.space.to.make.part.below....|
 // |.aligned.in.case.it.needs.more.than| (size of this area is unknown at
 // |.the.standard.16-byte.alignment....|  compile time; if present)