Debug Info: Simplify Frame Index handling in DBG_VALUE Machine Instructions

Rather than using the full power of target-specific addressing modes in
DBG_VALUEs with Frame Indicies, simply use Frame Index + Offset. This
reduces the complexity of debug info handling down to two
representations of values (reg+offset and frame index+offset) rather
than three or four.

Ideally we could ensure that frame indicies had been eliminated by the
time we reached an assembly or dwarf generation, but I haven't spent the
time to figure out where the FIs are leaking through into that & whether
there's a good place to convert them. Some FI+offset=>reg+offset
conversion is done (see PrologEpilogInserter, for example) which is
necessary for some SelectionDAG assumptions about registers, I believe,
but it might be possible to make this a more thorough conversion &
ensure there are no remaining FIs no matter how instruction selection
is performed.

llvm-svn: 184066

1 files changed, 17 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index eb80c648ee6..82f9f76baba 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -41,6 +41,7 @@
 
 #define DEBUG_TYPE "isel"
 #include "llvm/CodeGen/FastISel.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/Loads.h"
 #include "llvm/CodeGen/Analysis.h"
@@ -613,16 +614,14 @@ bool FastISel::SelectCall(const User *I) {
       return true;
     }
 
-    unsigned Reg = 0;
-    unsigned Offset = 0;
-    if (const Argument *Arg = dyn_cast<Argument>(Address)) {
+    Optional<MachineOperand> Op;
+    if (const Argument *Arg = dyn_cast<Argument>(Address))
       // Some arguments' frame index is recorded during argument lowering.
-      Offset = FuncInfo.getArgumentFrameIndex(Arg);
-      if (Offset)
-        Reg = TRI.getFrameRegister(*FuncInfo.MF);
-    }
-    if (!Reg)
-      Reg = lookUpRegForValue(Address);
+      if (int FI = FuncInfo.getArgumentFrameIndex(Arg))
+        Op = MachineOperand::CreateFI(FI);
+    if (!Op)
+      if (unsigned Reg = lookUpRegForValue(Address))
+        Op = MachineOperand::CreateReg(Reg, false);
 
     // If we have a VLA that has a "use" in a metadata node that's then used
     // here but it has no other uses, then we have a problem. E.g.,
@@ -635,16 +634,19 @@ bool FastISel::SelectCall(const User *I) {
     // If we assign 'a' a vreg and fast isel later on has to use the selection
     // DAG isel, it will want to copy the value to the vreg. However, there are
     // no uses, which goes counter to what selection DAG isel expects.
-    if (!Reg && !Address->use_empty() && isa<Instruction>(Address) &&
+    if (!Op && !Address->use_empty() && isa<Instruction>(Address) &&
         (!isa<AllocaInst>(Address) ||
          !FuncInfo.StaticAllocaMap.count(cast<AllocaInst>(Address))))
-      Reg = FuncInfo.InitializeRegForValue(Address);
+      Op = MachineOperand::CreateReg(FuncInfo.InitializeRegForValue(Address),
+                                      false);
+
+    if (Op && Op->isReg())
+      Op->setIsDebug(true);
 
-    if (Reg)
+    if (Op)
       BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
-              TII.get(TargetOpcode::DBG_VALUE))
-        .addReg(Reg, RegState::Debug).addImm(Offset)
-        .addMetadata(DI->getVariable());
+              TII.get(TargetOpcode::DBG_VALUE)).addOperand(*Op).addImm(0)
+          .addMetadata(DI->getVariable());
     else
       // We can't yet handle anything else here because it would require
       // generating code, thus altering codegen because of debug info.