Use the frame index side table for byval and inalloca arguments

Summary:
For inalloca functions, this is a very common code pattern:

  %argpack = type <{ i32, i32, i32 }>
  define void @f(%argpack* inalloca %args) {
  entry:
    %a = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 0
    %b = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 1
    %c = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 2
    tail call void @llvm.dbg.declare(metadata i32* %a, ... "a")
    tail call void @llvm.dbg.declare(metadata i32* %c, ... "b")
    tail call void @llvm.dbg.declare(metadata i32* %b, ... "c")

Even though these GEPs can be simplified to a constant offset from EBP
or RSP, we don't do that at -O0, and each GEP is computed into a
register. Registers used to compute argument addresses are typically
spilled and clobbered very quickly after the initial computation, so
live debug variable tracking loses information very quickly if we use
DBG_VALUE instructions.

This change moves processing of dbg.declare between argument lowering
and basic block isel, so that we can ask if an argument has a frame
index or not. If the argument lives in a register as is the case for
byval arguments on some targets, then we don't put it in the side table
and during ISel we emit DBG_VALUE instructions.

Reviewers: aprantl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32980

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302483 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 68 insertions, 41 deletions

diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index 8c98e3740f6..f37790d0983 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1150,16 +1150,16 @@ bool FastISel::selectIntrinsicCall(const IntrinsicInst *II) {
       return true;
     }
 
-    unsigned Offset = 0;
+    // Byval arguments with frame indices were already handled after argument
+    // lowering and before isel.
+    const auto *Arg =
+        dyn_cast<Argument>(Address->stripInBoundsConstantOffsets());
+    if (Arg && FuncInfo.getArgumentFrameIndex(Arg) != INT_MAX)
+      return true;
+
     Optional<MachineOperand> Op;
-    if (const auto *Arg = dyn_cast<Argument>(Address))
-      // Some arguments' frame index is recorded during argument lowering.
-      Offset = FuncInfo.getArgumentFrameIndex(Arg);
-    if (Offset)
-      Op = MachineOperand::CreateFI(Offset);
-    if (!Op)
-      if (unsigned Reg = lookUpRegForValue(Address))
-        Op = MachineOperand::CreateReg(Reg, false);
+    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.,
diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index cdf4d3a8b4e..606b8952f3c 100644
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -85,7 +85,6 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
   MF = &mf;
   TLI = MF->getSubtarget().getTargetLowering();
   RegInfo = &MF->getRegInfo();
-  MachineModuleInfo &MMI = MF->getMMI();
   const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
   unsigned StackAlign = TFI->getStackAlignment();
 
@@ -214,33 +213,6 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
         if (!isa<AllocaInst>(I) || !StaticAllocaMap.count(cast<AllocaInst>(&I)))
           InitializeRegForValue(&I);
 
-      // Collect llvm.dbg.declare information. This is done now instead of
-      // during the initial isel pass through the IR so that it is done
-      // in a predictable order.
-      if (const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I)) {
-        assert(DI->getVariable() && "Missing variable");
-        assert(DI->getDebugLoc() && "Missing location");
-        if (MMI.hasDebugInfo()) {
-          // Don't handle byval struct arguments or VLAs, for example.
-          // Non-byval arguments are handled here (they refer to the stack
-          // temporary alloca at this point).
-          const Value *Address = DI->getAddress();
-          if (Address) {
-            if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Address))
-              Address = BCI->getOperand(0);
-            if (const AllocaInst *AI = dyn_cast<AllocaInst>(Address)) {
-              DenseMap<const AllocaInst *, int>::iterator SI =
-                StaticAllocaMap.find(AI);
-              if (SI != StaticAllocaMap.end()) { // Check for VLAs.
-                int FI = SI->second;
-                MF->setVariableDbgInfo(DI->getVariable(), DI->getExpression(),
-                                       FI, DI->getDebugLoc());
-              }
-            }
-          }
-        }
-      }
-
       // Decide the preferred extend type for a value.
       PreferredExtendType[&I] = getPreferredExtendForValue(&I);
     }
@@ -510,12 +482,11 @@ void FunctionLoweringInfo::setArgumentFrameIndex(const Argument *A,
 /// If the argument does not have any assigned frame index then 0 is
 /// returned.
 int FunctionLoweringInfo::getArgumentFrameIndex(const Argument *A) {
-  DenseMap<const Argument *, int>::iterator I =
-    ByValArgFrameIndexMap.find(A);
+  auto I = ByValArgFrameIndexMap.find(A);
   if (I != ByValArgFrameIndexMap.end())
     return I->second;
   DEBUG(dbgs() << "Argument does not have assigned frame index!\n");
-  return 0;
+  return INT_MAX;
 }
 
 unsigned FunctionLoweringInfo::getCatchPadExceptionPointerVReg(
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 6aa755df147..7b566d518f7 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4676,7 +4676,8 @@ bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
   bool IsIndirect = false;
   Optional<MachineOperand> Op;
   // Some arguments' frame index is recorded during argument lowering.
-  if (int FI = FuncInfo.getArgumentFrameIndex(Arg))
+  int FI = FuncInfo.getArgumentFrameIndex(Arg);
+  if (FI != INT_MAX)
     Op = MachineOperand::CreateFI(FI);
 
   if (!Op && N.getNode()) {
@@ -4927,6 +4928,13 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
       return nullptr;
     }
 
+    // Byval arguments with frame indices were already handled after argument
+    // lowering and before isel.
+    const auto *Arg =
+        dyn_cast<Argument>(Address->stripInBoundsConstantOffsets());
+    if (Arg && FuncInfo.getArgumentFrameIndex(Arg) != INT_MAX)
+      return nullptr;
+
     SDValue &N = NodeMap[Address];
     if (!N.getNode() && isa<Argument>(Address))
       // Check unused arguments map.
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 3aabdaeaa09..c7eb9b80701 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -38,6 +38,7 @@
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineMemOperand.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineOperand.h"
 #include "llvm/CodeGen/MachinePassRegistry.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -1145,6 +1146,51 @@ static void createSwiftErrorEntriesInEntryBlock(FunctionLoweringInfo *FuncInfo,
   }
 }
 
+/// Collect llvm.dbg.declare information. This is done after argument lowering
+/// in case the declarations refer to arguments.
+static void processDbgDeclares(FunctionLoweringInfo *FuncInfo) {
+  MachineFunction *MF = FuncInfo->MF;
+  const DataLayout &DL = MF->getDataLayout();
+  for (const BasicBlock &BB : *FuncInfo->Fn) {
+    for (const Instruction &I : BB) {
+      const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I);
+      if (!DI)
+        continue;
+
+      assert(DI->getVariable() && "Missing variable");
+      assert(DI->getDebugLoc() && "Missing location");
+      const Value *Address = DI->getAddress();
+      if (!Address)
+        continue;
+
+      // Look through casts and constant offset GEPs. These mostly come from
+      // inalloca.
+      APInt Offset(DL.getPointerSizeInBits(0), 0);
+      Address = Address->stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
+
+      // Check if the variable is a static alloca or a byval or inalloca
+      // argument passed in memory. If it is not, then we will ignore this
+      // intrinsic and handle this during isel like dbg.value.
+      int FI = INT_MAX;
+      if (const auto *AI = dyn_cast<AllocaInst>(Address)) {
+        auto SI = FuncInfo->StaticAllocaMap.find(AI);
+        if (SI != FuncInfo->StaticAllocaMap.end())
+          FI = SI->second;
+      } else if (const auto *Arg = dyn_cast<Argument>(Address))
+        FI = FuncInfo->getArgumentFrameIndex(Arg);
+
+      if (FI == INT_MAX)
+        continue;
+
+      DIExpression *Expr = DI->getExpression();
+      if (Offset.getBoolValue())
+        Expr = DIExpression::prepend(Expr, DIExpression::NoDeref,
+                                     Offset.getZExtValue());
+      MF->setVariableDbgInfo(DI->getVariable(), Expr, FI, DI->getDebugLoc());
+    }
+  }
+}
+
 /// Propagate swifterror values through the machine function CFG.
 static void propagateSwiftErrorVRegs(FunctionLoweringInfo *FuncInfo) {
   auto *TLI = FuncInfo->TLI;
@@ -1317,6 +1363,8 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
   }
   createSwiftErrorEntriesInEntryBlock(FuncInfo, FastIS, TLI, TII, SDB);
 
+  processDbgDeclares(FuncInfo);
+
   // Iterate over all basic blocks in the function.
   for (const BasicBlock *LLVMBB : RPOT) {
     if (OptLevel != CodeGenOpt::None) {