[codeview] Emit S_FRAMEPROC and use S_DEFRANGE_FRAMEPOINTER_REL

Summary:
Before this change, LLVM would always describe locals on the stack as
being relative to some specific register, RSP, ESP, EBP, ESI, etc.
Variables in stack memory are pretty common, so there is a special
S_DEFRANGE_FRAMEPOINTER_REL symbol for them. This change uses it to
reduce the size of our debug info.

On top of the size savings, there are cases on 32-bit x86 where local
variables are addressed from ESP, but ESP changes across the function.
Unlike in DWARF, there is no FPO data to describe the stack adjustments
made to push arguments onto the stack and pop them off after the call,
which makes it hard for the debugger to find the local variables in
frames further up the stack.

To handle this, CodeView has a special VFRAME register, which
corresponds to the $T0 variable set by our FPO data in 32-bit.  Offsets
to local variables are instead relative to this value.

This is part of PR38857.

Reviewers: hans, zturner, javed.absar

Subscribers: aprantl, hiraditya, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D52217

llvm-svn: 343543

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
index 20533f90954..88e2f16d3fd 100644
--- a/llvm/lib/CodeGen/MIRPrinter.cpp
+++ b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -328,6 +328,8 @@ void MIRPrinter::convert(ModuleSlotTracker &MST,
   YamlMFI.HasCalls = MFI.hasCalls();
   YamlMFI.MaxCallFrameSize = MFI.isMaxCallFrameSizeComputed()
     ? MFI.getMaxCallFrameSize() : ~0u;
+  YamlMFI.CVBytesOfCalleeSavedRegisters =
+      MFI.getCVBytesOfCalleeSavedRegisters();
   YamlMFI.HasOpaqueSPAdjustment = MFI.hasOpaqueSPAdjustment();
   YamlMFI.HasVAStart = MFI.hasVAStart();
   YamlMFI.HasMustTailInVarArgFunc = MFI.hasMustTailInVarArgFunc();