[PATCH] D72969: [WebAssembly] Track frame registers through VReg and local allocation

[Derek Schuff via Phabricator via llvm-commits]

dschuff created this revision.
Herald added subscribers: llvm-commits, sunfish, aheejin, hiraditya, jgravelle-google, sbc100, aprantl, MatzeB.
Herald added a project: LLVM.

This change has 2 components:

Target-independent: add a method getDwarfFrameBase to TargetFrameLowering. It
describes how the Dwarf frame base will be encoded.  That can be a register (the
default), the CFA (which replaces NVPTX-specific logic in DwarfCompileUnit), or
a DW_OP_WASM_location descriptr.

WebAssembly: Allow WebAssemblyFunctionInfo::getFrameRegister to return the
correct virtual register instead of FP32/SP32 after WebAssemblyReplacePhysRegs
has run.  Make WebAssemblyExplicitLocals store the local it allocates for the
frame register. Use this local information to implement getDwarfFrameBase

The result is that the DW_AT_frame_base attribute is correctly encoded for each
subprogram, and each param and local variable has a correct DW_AT_location that
uses DW_OP_fbreg to refer to the frame base.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72969

Files:
  llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp


Index: llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
@@ -21,6 +21,7 @@
 
 #include "WebAssembly.h"
 #include "WebAssemblySubtarget.h"
+#include "WebAssemblyMachineFunctionInfo.h"
 #include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -83,10 +84,20 @@
   for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) {
     unsigned Reg = Register::index2VirtReg(I);
     auto &TRI = *MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
-    if (MRI.reg_nodbg_empty(Reg) || Reg == TRI.getFrameRegister(MF))
+
+    if (MRI.reg_nodbg_empty(Reg))
       continue;
 
     LIS.splitSeparateComponents(LIS.getInterval(Reg), SplitLIs);
+    if (Reg == TRI.getFrameRegister(MF) && SplitLIs.size() > 0) {
+      // The live interval for the frame register was split, resulting in a new
+      // VReg. For now we only support debug info output for a single frame base
+      // value for the function, so just use the last one. It will certainly be
+      // wrong for some part of the function, but until we are able to track
+      // values through live-range splitting and stackification, it will have to
+      // do.
+      MF.getInfo<WebAssemblyFunctionInfo>()->setFrameBaseVreg(SplitLIs.back()->reg);
+    }
     SplitLIs.clear();
   }
 
@@ -104,5 +115,5 @@
     }
   }
 
-  return false;
+  return true;
 }


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