[WebAssembly] Use LiveDebugValues analysis

This enables `LiveDebugValues` analysis for Wasm. `DBG_VALUE`s expire at
the end of a BB, and this is the analysis extends their lifetime when
possible, greatly increasing the coverage of variable debug info.

Specifically, this removes the current constraint that this analysis is
only used with physical registers, which was first introduced in D18421,
because Wasm uses only virtual registers. I don't think there's anything
inherent in this analysis that only applies to physical registers; it
was just because all targets using this analysis ran this at the end of
their compiliation pipeline, at which point all their vregs had been
allocated, and Wasm's debug info infrastructure was not really set up
yet, so it was not using it.

This adds supports to Wasm-specific target-index operands, defined in
https://github.com/llvm/llvm-project/blob/2166d9529a60d1cdedb733d2e4134c971f0969ec/llvm/lib/Target/WebAssembly/WebAssembly.h#L87-L100.
Among these, `TI_LOCAL`, `TI_LOCAL_INDIRECT`, and `TI_OPERAND_STACK` are
used by Wasm `DBG_VALUE` instructions.

This does not yet handle mutable target indices, i.e., this does not
terminate a `DBG_VALUE` for a local index when we encounter a new
`local.set` or `local.tee`. It will be implemented as a follow-up.

Reviewed By: dschuff, jmorse

Differential Revision: https://reviews.llvm.org/D138943

1 files changed, 9 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
index 141008ac2296..9dba9a88f703 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Pass.h"
 #include "llvm/PassRegistry.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Target/TargetMachine.h"
 
 /// \file LiveDebugValues.cpp
 ///
@@ -72,11 +73,6 @@ public:
   /// Calculate the liveness information for the given machine function.
   bool runOnMachineFunction(MachineFunction &MF) override;
 
-  MachineFunctionProperties getRequiredProperties() const override {
-    return MachineFunctionProperties().set(
-        MachineFunctionProperties::Property::NoVRegs);
-  }
-
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     MachineFunctionPass::getAnalysisUsage(AU);
@@ -106,6 +102,14 @@ LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
 }
 
 bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
+  // Except for Wasm, all targets should be only using physical register at this
+  // point. Wasm only use virtual registers throught its pipeline, but its
+  // virtual registers don't participate  in this LiveDebugValues analysis; only
+  // its target indices do.
+  assert(MF.getTarget().getTargetTriple().isWasm() ||
+         MF.getProperties().hasProperty(
+             MachineFunctionProperties::Property::NoVRegs));
+
   bool InstrRefBased = MF.useDebugInstrRef();
   // Allow the user to force selection of InstrRef LDV.
   InstrRefBased |= ForceInstrRefLDV;