MIR Serialization: Initial serialization of stack objects.

This commit implements the initial serialization of stack objects from the
MachineFrameInfo class. It can only serialize the ordinary stack objects
(including ordinary spill slots), but it doesn't serialize variable sized or
fixed stack objects yet.

The stack objects are serialized using a YAML sequence of YAML inline mappings.
Each mapping has the object's ID, type, size, offset and alignment. The stack
objects are a part of machine function's YAML mapping.

Reviewers: Duncan P. N. Exon Smith


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241922 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/MIR/X86/stack-objects.mir

@@ -0,0 +1,39 @@
+# RUN: llc -march=x86-64 -start-after branch-folder -stop-after branch-folder -o /dev/null %s | FileCheck %s
+# This test ensures that the MIR parser parses stack objects correctly.
+
+--- |
+
+  define i32 @test(i32 %a) #0 {
+  entry:
+    %b = alloca i32
+    %x = alloca i64
+    store i32 %a, i32* %b
+    store i64 2, i64* %x
+    %c = load i32, i32* %b
+    ret i32 %c
+  }
+
+  attributes #0 = { "no-frame-pointer-elim"="false" }
+
+...
+---
+name:            test
+frameInfo:
+  maxAlignment:    8
+# CHECK: stack:
+# CHECK-NEXT: - { id: 0, offset: -12, size: 4, alignment: 4 }
+# CHECK-NEXT: - { id: 1, offset: -24, size: 8, alignment: 8 }
+# CHECK-NEXT: - { id: 2, type: spill-slot, offset: -32, size: 4, alignment: 4 }
+stack:
+  - { id: 0, offset: -12, size: 4, alignment: 4 }
+  - { id: 1, offset: -24, size: 8, alignment: 8 }
+  - { id: 2, type: spill-slot, offset: -32, size: 4, alignment: 4 }
+body:
+  - id:          0
+    name:        entry
+    instructions:
+      - 'MOV32mr %rsp, 1, _, -4, _, %edi'
+      - 'MOV64mi32 %rsp, 1, _, -16, _, 2'
+      - '%eax = MOV32rm %rsp, 1, _, -4, _'
+      - 'RETQ %eax'
+...