Fix for http://llvm.org/bugs/show_bug.cgi?id=18590

This patch fixes the bug in peephole optimization that folds a load which defines one vreg into the one and only use of that vreg. With debug info, a DBG_VALUE that referenced the vreg considered to be a use, preventing the optimization. The fix is to ignore DBG_VALUE's during the optimization, and undef a DBG_VALUE that references a vreg that gets removed.
Patch by Trevor Smigiel!

llvm-svn: 203829

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 4029f4a2bbc..3dabcbed7fc 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -414,3 +414,18 @@ bool MachineRegisterInfo::isConstantPhysReg(unsigned PhysReg,
       return false;
   return true;
 }
+
+/// markUsesInDebugValueAsUndef - Mark every DBG_VALUE referencing the
+/// specified register as undefined which causes the DBG_VALUE to be
+/// deleted during LiveDebugVariables analysis.
+void MachineRegisterInfo::markUsesInDebugValueAsUndef(unsigned Reg) const {
+  // Mark any DBG_VALUE that uses Reg as undef (but don't delete it.)
+  MachineRegisterInfo::use_iterator nextI;
+  for (use_iterator I = use_begin(Reg), E = use_end(); I != E; I = nextI) {
+    nextI = std::next(I);  // I is invalidated by the setReg
+    MachineOperand& Use = I.getOperand();
+    MachineInstr *UseMI = Use.getParent();
+    if (UseMI->isDebugValue())
+      UseMI->getOperand(0).setReg(0U);
+  }
+}