[STACKMAPS] Document+test UINT64_MAX stack size.

When a function does a dynamic stack allocation, the function's stack
size (in the stack map) is reported as UINT64_MAX.

This change tests and documents this property.

Differential Revision: https://reviews.llvm.org/D128525

llvm/docs/StackMaps.rst

@@ -328,7 +328,7 @@ format of this section follows:
   uint32 : NumRecords
   StkSizeRecord[NumFunctions] {
     uint64 : Function Address
-    uint64 : Stack Size
+    uint64 : Stack Size (or UINT64_MAX if not statically known)
     uint64 : Record Count
   }
   Constants[NumConstants] {

llvm/test/CodeGen/AArch64/stackmap-dynamic-alloca.ll

@@ -0,0 +1,30 @@
+; RUN: llc < %s -mtriple=arm64-linux-gnu | FileCheck %s
+
+; When a function does a dynamic stack allocation, the function's stack size
+; is reported as UINT64_MAX.
+
+; CHECK-LABEL:  .section  .llvm_stackmaps
+; CHECK-NEXT:  __LLVM_StackMaps:
+; Header
+; CHECK-NEXT:   .byte 3
+; CHECK-NEXT:   .byte 0
+; CHECK-NEXT:   .hword 0
+; Num Functions
+; CHECK-NEXT:   .word 1
+; Num LargeConstants
+; CHECK-NEXT:   .word 0
+; Num Callsites
+; CHECK-NEXT:   .word 1
+
+; Functions and stack size
+; CHECK-NEXT:   .xword f
+; CHECK-NEXT:   .xword -1
+
+define void @f(i32 %nelems) {
+entry:
+  %mem = alloca i32, i32 %nelems
+  call void (i64, i32, ...) @llvm.experimental.stackmap(i64 0, i32 0, i32* %mem)
+  ret void
+}
+
+declare void @llvm.experimental.stackmap(i64, i32, ...)

llvm/test/CodeGen/SystemZ/stackmap-dynamic-alloca.ll

@@ -0,0 +1,30 @@
+; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+
+; When a function does a dynamic stack allocation, the function's stack size
+; is reported as UINT64_MAX.
+
+; CHECK:       .section .llvm_stackmaps
+; CHECK-NEXT:  __LLVM_StackMaps:
+; Header
+; CHECK-NEXT:   .byte 3
+; CHECK-NEXT:   .byte 0
+; CHECK-NEXT:   .short 0
+; Num Functions
+; CHECK-NEXT:   .long 1
+; Num LargeConstants
+; CHECK-NEXT:   .long 0
+; Num Callsites
+; CHECK-NEXT:   .long 1
+
+; Functions and stack size
+; CHECK-NEXT:   .quad f
+; CHECK-NEXT:   .quad -1
+
+define void @f(i32 %nelems) {
+entry:
+  %mem = alloca i32, i32 %nelems
+  call void (i64, i32, ...) @llvm.experimental.stackmap(i64 0, i32 0, i32* %mem)
+  ret void
+}
+
+declare void @llvm.experimental.stackmap(i64, i32, ...)

llvm/test/CodeGen/X86/stackmap-dynamic-alloca.ll

@@ -0,0 +1,30 @@
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=corei7 | FileCheck %s
+
+; When a function does a dynamic stack allocation, the function's stack size is
+; reported as UINT64_MAX.
+
+; CHECK-LABEL:  .section  __LLVM_STACKMAPS,__llvm_stackmaps
+; CHECK-NEXT:  __LLVM_StackMaps:
+; Header
+; CHECK-NEXT:   .byte 3
+; CHECK-NEXT:   .byte 0
+; CHECK-NEXT:   .short 0
+; Num Functions
+; CHECK-NEXT:   .long 1
+; Num LargeConstants
+; CHECK-NEXT:   .long 0
+; Num Callsites
+; CHECK-NEXT:   .long 1
+
+; Functions and stack size
+; CHECK-NEXT:   .quad _f
+; CHECK-NEXT:   .quad -1
+
+define void @f(i32 %nelems) {
+entry:
+  %mem = alloca i32, i32 %nelems
+  call void (i64, i32, ...) @llvm.experimental.stackmap(i64 0, i32 0, i32* %mem)
+  ret void
+}
+
+declare void @llvm.experimental.stackmap(i64, i32, ...)