Reapply "[SelectionDAG] Selection of DBG_VALUE using a PHI node result (pt 2)"

Summary:
This reverts SVN r331441 (reapplies r331337), together with a fix
in to handle an already existing fragment expression in the
dbg.value that must be fragmented due to a split PHI node.

This should solve the problem seen in PR37321, which was the
reason for the revert of r331337.

The situation in PR37321 is that we have a PHI node like this

   %u.sroa = phi i80 [ %u.sroa.x, %if.x ],
                     [ %u.sroa.y, %if.y ],
                     [ %u.sroa.z, %if.z ]

and a dbg.value like this

  call void @llvm.dbg.value(metadata i80 %u.sroa,
                            metadata !13,
                            metadata !DIExpression(DW_OP_LLVM_fragment, 0, 80))

The phi node is split into three 32-bit PHI nodes

  %30:gr32 = PHI %11:gr32, %bb.4, %14:gr32, %bb.5, %27:gr32, %bb.8
  %31:gr32 = PHI %12:gr32, %bb.4, %15:gr32, %bb.5, %28:gr32, %bb.8
  %32:gr32 = PHI %13:gr32, %bb.4, %16:gr32, %bb.5, %29:gr32, %bb.8

but since the original value only is 80 bits we need to adjust the size
of the last fragment expression, and with this patch we get

  DBG_VALUE debug-use %30:gr32, debug-use $noreg, !"u", !DIExpression(DW_OP_LLVM_fragment, 0, 32)
  DBG_VALUE debug-use %31:gr32, debug-use $noreg, !"u", !DIExpression(DW_OP_LLVM_fragment, 32, 32)
  DBG_VALUE debug-use %32:gr32, debug-use $noreg, !"u", !DIExpression(DW_OP_LLVM_fragment, 64, 16)

Reviewers: vsk, aprantl, mstorsjo

Reviewed By: aprantl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D46384

llvm-svn: 331464

1 files changed, 42 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 58d323a3e5f..59a1d6e9753 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5257,12 +5257,48 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     // PHI nodes have already been selected, so we should know which VReg that
     // is assigns to already.
     if (isa<PHINode>(V)) {
-      auto It = FuncInfo.ValueMap.find(V);
-      if (It != FuncInfo.ValueMap.end()) {
-        unsigned Reg = It->second;
-        SDV = DAG.getVRegDbgValue(Variable, Expression, Reg, false, dl,
-                                  SDNodeOrder);
-        DAG.AddDbgValue(SDV, nullptr, false);
+      auto VMI = FuncInfo.ValueMap.find(V);
+      if (VMI != FuncInfo.ValueMap.end()) {
+        unsigned Reg = VMI->second;
+        // The PHI node may be split up into several MI PHI nodes (in
+        // FunctionLoweringInfo::set).
+        RegsForValue RFV(V->getContext(), TLI, DAG.getDataLayout(), Reg,
+                         V->getType(), false);
+        if (RFV.occupiesMultipleRegs()) {
+          unsigned I = 0;
+          unsigned Offset = 0;
+          unsigned BitsToDescribe = 0;
+          if (auto VarSize = Variable->getSizeInBits())
+            BitsToDescribe = *VarSize;
+          if (auto Fragment = Expression->getFragmentInfo())
+            BitsToDescribe = Fragment->SizeInBits;
+          for (auto CountAndVT : zip_first(RFV.RegCount, RFV.RegVTs)) {
+            unsigned RegCount = std::get<0>(CountAndVT);
+            MVT RegisterVT = std::get<1>(CountAndVT);
+            unsigned RegisterSize = RegisterVT.getSizeInBits();
+            for (unsigned E = I + RegCount; I != E; ++I) {
+              // Bail out if all bits already are described.
+              if (Offset >= BitsToDescribe)
+                break;
+              unsigned FragmentSize = (Offset + RegisterSize > BitsToDescribe)
+                  ? BitsToDescribe - Offset
+                  : RegisterSize;
+              auto FragmentExpr = DIExpression::createFragmentExpression(
+                  Expression, Offset, FragmentSize);
+              if (!FragmentExpr)
+                continue;
+              // The vregs are guaranteed to be allocated in sequence.
+              SDV = DAG.getVRegDbgValue(Variable, *FragmentExpr, Reg + I,
+                                        false, dl, SDNodeOrder);
+              DAG.AddDbgValue(SDV, nullptr, false);
+              Offset += RegisterSize;
+            }
+          }
+        } else {
+          SDV = DAG.getVRegDbgValue(Variable, Expression, Reg, false, dl,
+                                    SDNodeOrder);
+          DAG.AddDbgValue(SDV, nullptr, false);
+        }
         return nullptr;
       }
     }