[PATCH] Explicitly report runtime stack realignment in StackMap section

[Philip Reames]

Hi atrick, nadav, ributzka,

This change adds code to explicitly mark a function which requires runtime stack realignment as not having a fixed frame size in the StackMap section.  As it happens, this is not actually a functional change.  The size that would be reported without the check is also "-1", but as far as I can tell, that's an accident.  The code change makes this explicit.  

If we decide not to merge the  code change, adding the test case to ensure this behaviour is preserved is worthwhile.  

Note: There's a separate bug in handling of stackmaps and patchpoints in functions which need dynamic frame realignment.  The current code assumes that offsets can be calculated from RBP, but realigned frames must use RSP.  (There's a variable gap between RBP and the spill slots.)  This change set does not address that issue.

http://reviews.llvm.org/D4572

Files:
  lib/CodeGen/StackMaps.cpp
  test/CodeGen/X86/stackmap.ll

Index: lib/CodeGen/StackMaps.cpp
===================================================================
--- lib/CodeGen/StackMaps.cpp
+++ lib/CodeGen/StackMaps.cpp
@@ -236,8 +236,11 @@
 
   // Record the stack size of the current function.
   const MachineFrameInfo *MFI = AP.MF->getFrameInfo();
+  const TargetRegisterInfo *RegInfo = AP.MF->getTarget().getRegisterInfo();
+  const bool DynamicFrameSize = MFI->hasVarSizedObjects() ||
+    RegInfo->needsStackRealignment(*(AP.MF));
   FnStackSize[AP.CurrentFnSym] =
-    MFI->hasVarSizedObjects() ? UINT64_MAX : MFI->getStackSize();
+    DynamicFrameSize ? UINT64_MAX : MFI->getStackSize();
 }
 
 void StackMaps::recordStackMap(const MachineInstr &MI) {
Index: test/CodeGen/X86/stackmap.ll
===================================================================
--- test/CodeGen/X86/stackmap.ll
+++ test/CodeGen/X86/stackmap.ll
@@ -9,11 +9,11 @@
 ; CHECK-NEXT:   .byte 0
 ; CHECK-NEXT:   .short 0
 ; Num Functions
-; CHECK-NEXT:   .long 15
+; CHECK-NEXT:   .long 16
 ; Num LargeConstants
 ; CHECK-NEXT:   .long 3
 ; Num Callsites
-; CHECK-NEXT:   .long 19
+; CHECK-NEXT:   .long 20
 
 ; Functions and stack size
 ; CHECK-NEXT:   .quad _constantargs
@@ -46,6 +46,8 @@
 ; CHECK-NEXT:   .quad 8
 ; CHECK-NEXT:   .quad _clobberScratch
 ; CHECK-NEXT:   .quad 56
+; CHECK-NEXT:   .quad _needsStackRealignment
+; CHECK-NEXT:   .quad -1
 
 ; Large Constants
 ; CHECK-NEXT:   .quad   2147483648
@@ -464,6 +466,23 @@
   ret void
 }
 
+; A stack frame which needs to be realigned at runtime (to meet alignment 
+; criteria for values on the stack) does not have a fixed frame size. 
+; CHECK-LABEL:  .long L{{.*}}-_needsStackRealignment
+; CHECK-NEXT:   .short 0
+; 0 locations
+; CHECK-NEXT:   .short 0
+define void @needsStackRealignment() {
+  %val = alloca i64, i32 3, align 128
+  tail call void (...)* @escape_values(i64* %val)
+; Note: Adding any non-constant to the stackmap would fail because we
+; expected to be able to address off the frame pointer.  In a realigned
+; frame, we must use the stack pointer instead.  This is a separate bug.
+  tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 0)
+  ret void
+}
+declare void @escape_values(...)
+
 declare void @llvm.experimental.stackmap(i64, i32, ...)
 declare void @llvm.experimental.patchpoint.void(i64, i32, i8*, i32, ...)
 declare i64 @llvm.experimental.patchpoint.i64(i64, i32, i8*, i32, ...)
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