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

1 files changed, 23 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues.cpp
index b9937e5..d3cbac8 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());
+    }
   }
 }