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

llvm-svn: 302483

1 files changed, 2 insertions, 31 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index cdf4d3a8b4e..606b8952f3c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/llvm/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(