Merging r326769 and r326780:

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r326769 | bjope | 2018-03-06 00:47:07 -0800 (Tue, 06 Mar 2018) | 28 lines

[DebugInfo] Discard invalid DBG_VALUE instructions in LiveDebugVariables

Summary:
This is a workaround for pr36417
https://bugs.llvm.org/show_bug.cgi?id=36417

LiveDebugVariables will now verify that the DBG_VALUE instructions
are sane (prior to register allocation) by asking LIS if a virtual
register used in the DBG_VALUE is live (or dead def) in the slot
index before the DBG_VALUE. If it isn't sane the DBG_VALUE is
discarded.

One pass that was identified as introducing non-sane DBG_VALUE
instructtons, when analysing pr36417, was the DAG->DAG Instruction
Selection. It sometimes inserts DBG_VALUE instructions referring to
a virtual register that is defined later in the same basic block.
So it is a use before def kind of problem. The DBG_VALUE is
typically inserted in the beginning of a basic block when this
happens. The problem can be seen in the test case
test/DebugInfo/X86/dbg-value-inlined-parameter.ll

Reviewers: aprantl, rnk, probinson

Reviewed By: aprantl

Subscribers: vsk, davide, alexcrichton, Ka-Ka, eraman, llvm-commits, JDevlieghere

Differential Revision: https://reviews.llvm.org/D43956
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r326780 | bjope | 2018-03-06 05:23:28 -0800 (Tue, 06 Mar 2018) | 6 lines

Fixup for rL326769 (RegState::Debug is being truncated to a bool)

I obviously messed up arguments to MachineOperand::CreateReg
in rL326769. This should make it work as intended.

Thanks to RKSimon for spotting this.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@329668 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 1 deletions

diff --git a/lib/CodeGen/LiveDebugVariables.cpp b/lib/CodeGen/LiveDebugVariables.cpp
index 75e3d35169c..4ffcffcea69 100644
--- a/lib/CodeGen/LiveDebugVariables.cpp
+++ b/lib/CodeGen/LiveDebugVariables.cpp
@@ -514,6 +514,39 @@ bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
     return false;
   }
 
+  // Detect invalid DBG_VALUE instructions, with a debug-use of a virtual
+  // register that hasn't been defined yet. If we do not remove those here, then
+  // the re-insertion of the DBG_VALUE instruction after register allocation
+  // will be incorrect.
+  // TODO: If earlier passes are corrected to generate sane debug information
+  // (and if the machine verifier is improved to catch this), then these checks
+  // could be removed or replaced by asserts.
+  bool Discard = false;
+  if (MI.getOperand(0).isReg() &&
+      TargetRegisterInfo::isVirtualRegister(MI.getOperand(0).getReg())) {
+    const unsigned Reg = MI.getOperand(0).getReg();
+    if (!LIS->hasInterval(Reg)) {
+      // The DBG_VALUE is described by a virtual register that does not have a
+      // live interval. Discard the DBG_VALUE.
+      Discard = true;
+      DEBUG(dbgs() << "Discarding debug info (no LIS interval): "
+            << Idx << " " << MI);
+    } else {
+      // The DBG_VALUE is only valid if either Reg is live out from Idx, or Reg
+      // is defined dead at Idx (where Idx is the slot index for the instruction
+      // preceeding the DBG_VALUE).
+      const LiveInterval &LI = LIS->getInterval(Reg);
+      LiveQueryResult LRQ = LI.Query(Idx);
+      if (!LRQ.valueOutOrDead()) {
+        // We have found a DBG_VALUE with the value in a virtual register that
+        // is not live. Discard the DBG_VALUE.
+        Discard = true;
+        DEBUG(dbgs() << "Discarding debug info (reg not live): "
+              << Idx << " " << MI);
+      }
+    }
+  }
+
   // Get or create the UserValue for (variable,offset) here.
   bool IsIndirect = MI.getOperand(1).isImm();
   if (IsIndirect)
@@ -522,7 +555,13 @@ bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
   const DIExpression *Expr = MI.getDebugExpression();
   UserValue *UV =
       getUserValue(Var, Expr, MI.getDebugLoc());
-  UV->addDef(Idx, MI.getOperand(0), IsIndirect);
+  if (!Discard)
+    UV->addDef(Idx, MI.getOperand(0), IsIndirect);
+  else {
+    MachineOperand MO = MachineOperand::CreateReg(0U, false);
+    MO.setIsDebug();
+    UV->addDef(Idx, MO, false);
+  }
   return true;
 }