Consider regmasks when computing register-based DBG_VALUE live ranges

Now register parameters that aren't saved to the stack or CSRs are
considered dead after the first call. Previously the debugger would show
whatever was in the register.

Fixes PR26589

Reviewers: aprantl

Differential Revision: http://reviews.llvm.org/D17211

llvm-svn: 264429

2 files changed, 63 insertions, 33 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
index 5ce255001f8..21d816bc997 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
@@ -15,7 +15,9 @@
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
 #include <algorithm>
 #include <map>
 using namespace llvm;
@@ -122,26 +124,6 @@ static void clobberRegisterUses(RegDescribedVarsMap &RegVars, unsigned RegNo,
   clobberRegisterUses(RegVars, I, HistMap, ClobberingInstr);
 }
 
-// \brief Collect all registers clobbered by @MI and apply the functor
-// @Func to their RegNo.
-// @Func should be a functor with a void(unsigned) signature. We're
-// not using std::function here for performance reasons. It has a
-// small but measurable impact. By using a functor instead of a
-// std::set& here, we can avoid the overhead of constructing
-// temporaries in calculateDbgValueHistory, which has a significant
-// performance impact.
-template<typename Callable>
-static void applyToClobberedRegisters(const MachineInstr &MI,
-                                      const TargetRegisterInfo *TRI,
-                                      Callable Func) {
-  for (const MachineOperand &MO : MI.operands()) {
-    if (!MO.isReg() || !MO.isDef() || !MO.getReg())
-      continue;
-    for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI)
-      Func(*AI);
-  }
-}
-
 // \brief Returns the first instruction in @MBB which corresponds to
 // the function epilogue, or nullptr if @MBB doesn't contain an epilogue.
 static const MachineInstr *getFirstEpilogueInst(const MachineBasicBlock &MBB) {
@@ -173,10 +155,23 @@ static void collectChangingRegs(const MachineFunction *MF,
     auto FirstEpilogueInst = getFirstEpilogueInst(MBB);
 
     for (const auto &MI : MBB) {
+      // Avoid looking at prologue or epilogue instructions.
       if (&MI == FirstEpilogueInst)
         break;
-      if (!MI.getFlag(MachineInstr::FrameSetup))
-        applyToClobberedRegisters(MI, TRI, [&](unsigned r) { Regs.set(r); });
+      if (MI.getFlag(MachineInstr::FrameSetup))
+        continue;
+
+      // Look for register defs and register masks. Register masks are
+      // typically on calls and they clobber everything not in the mask.
+      for (const MachineOperand &MO : MI.operands()) {
+        if (MO.isReg() && MO.isDef() && MO.getReg()) {
+          for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid();
+               ++AI)
+            Regs.set(*AI);
+        } else if (MO.isRegMask()) {
+          Regs.setBitsNotInMask(MO.getRegMask());
+        }
+      }
     }
   }
 }
@@ -187,16 +182,35 @@ void llvm::calculateDbgValueHistory(const MachineFunction *MF,
   BitVector ChangingRegs(TRI->getNumRegs());
   collectChangingRegs(MF, TRI, ChangingRegs);
 
+  const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
+  unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
   RegDescribedVarsMap RegVars;
   for (const auto &MBB : *MF) {
     for (const auto &MI : MBB) {
       if (!MI.isDebugValue()) {
         // Not a DBG_VALUE instruction. It may clobber registers which describe
         // some variables.
-        applyToClobberedRegisters(MI, TRI, [&](unsigned RegNo) {
-          if (ChangingRegs.test(RegNo))
-            clobberRegisterUses(RegVars, RegNo, Result, MI);
-        });
+        for (const MachineOperand &MO : MI.operands()) {
+          if (MO.isReg() && MO.isDef() && MO.getReg()) {
+            // If this is a register def operand, it may end a debug value
+            // range.
+            for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid();
+                 ++AI)
+              if (ChangingRegs.test(*AI))
+                clobberRegisterUses(RegVars, *AI, Result, MI);
+          } else if (MO.isRegMask()) {
+            // If this is a register mask operand, clobber all debug values in
+            // non-CSRs.
+            for (int I = ChangingRegs.find_first(); I != -1;
+                 I = ChangingRegs.find_next(I)) {
+              // Don't consider SP to be clobbered by register masks.
+              if (unsigned(I) != SP && TRI->isPhysicalRegister(I) &&
+                  MO.clobbersPhysReg(I)) {
+                clobberRegisterUses(RegVars, I, Result, MI);
+              }
+            }
+          }
+        }
         continue;
       }
 
diff --git a/llvm/lib/CodeGen/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues.cpp
index b9937e5570d..d3cbac8cc17 100644
--- a/llvm/lib/CodeGen/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues.cpp
@@ -30,6 +30,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include <queue>
@@ -208,18 +209,33 @@ void LiveDebugValues::transferDebugValue(MachineInstr &MI,
 /// A definition of a register may mark the end of a range.
 void LiveDebugValues::transferRegisterDef(MachineInstr &MI,
                                           VarLocList &OpenRanges) {
+  MachineFunction *MF = MI.getParent()->getParent();
+  const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
+  unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
   for (const MachineOperand &MO : MI.operands()) {
-    if (!(MO.isReg() && MO.isDef() && MO.getReg() &&
-          TRI->isPhysicalRegister(MO.getReg())))
-      continue;
-    // Remove ranges of all aliased registers.
-    for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
+    if (MO.isReg() && MO.isDef() && MO.getReg() &&
+        TRI->isPhysicalRegister(MO.getReg())) {
+      // Remove ranges of all aliased registers.
+      for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
+        OpenRanges.erase(std::remove_if(OpenRanges.begin(), OpenRanges.end(),
+                                        [&](const VarLoc &V) {
+                                          return (*RAI ==
+                                                  isDescribedByReg(*V.MI));
+                                        }),
+                         OpenRanges.end());
+    } else if (MO.isRegMask()) {
+      // Remove ranges of all clobbered registers. Register masks don't usually
+      // list SP as preserved.  While the debug info may be off for an
+      // instruction or two around callee-cleanup calls, transferring the
+      // DEBUG_VALUE across the call is still a better user experience.
       OpenRanges.erase(std::remove_if(OpenRanges.begin(), OpenRanges.end(),
                                       [&](const VarLoc &V) {
-                                        return (*RAI ==
-                                                isDescribedByReg(*V.MI));
+                                        unsigned Reg = isDescribedByReg(*V.MI);
+                                        return Reg && Reg != SP &&
+                                               MO.clobbersPhysReg(Reg);
                                       }),
                        OpenRanges.end());
+    }
   }
 }