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

3 files changed, 27 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
index bbb4da83305..643efc2a4f9 100644
--- a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -127,17 +127,7 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
           unsigned Reg = MO.getReg();
           if (!TargetRegisterInfo::isVirtualRegister(Reg))
             continue;
-          MachineRegisterInfo::use_iterator nextI;
-          for (MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg),
-               E = MRI->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==MI)
-              continue;
-            assert(Use.isDebug());
-            UseMI->getOperand(0).setReg(0U);
-          }
+          MRI->markUsesInDebugValueAsUndef(Reg);
         }
         AnyChanges = true;
         MI->eraseFromParent();
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);
+  }
+}
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 18af9d480c7..8bf2270755e 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -505,12 +505,12 @@ bool PeepholeOptimizer::isLoadFoldable(MachineInstr *MI,
     return false;
 
   unsigned Reg = MI->getOperand(0).getReg();
-  // To reduce compilation time, we check MRI->hasOneUse when inserting
+  // To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting
   // loads. It should be checked when processing uses of the load, since
   // uses can be removed during peephole.
   if (!MI->getOperand(0).getSubReg() &&
       TargetRegisterInfo::isVirtualRegister(Reg) &&
-      MRI->hasOneUse(Reg)) {
+      MRI->hasOneNonDBGUse(Reg)) {
     FoldAsLoadDefReg = Reg;
     return true;
   }
@@ -594,10 +594,14 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
       ++MII;
       LocalMIs.insert(MI);
 
+      // Skip debug values. They should not affect this peephole optimization.
+      if (MI->isDebugValue())
+          continue;
+
       // If there exists an instruction which belongs to the following
       // categories, we will discard the load candidate.
       if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() ||
-          MI->isKill() || MI->isInlineAsm() || MI->isDebugValue() ||
+          MI->isKill() || MI->isInlineAsm() ||
           MI->hasUnmodeledSideEffects()) {
         FoldAsLoadDefReg = 0;
         continue;
@@ -633,6 +637,9 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
       if (!isLoadFoldable(MI, FoldAsLoadDefReg) && FoldAsLoadDefReg) {
         // We need to fold load after optimizeCmpInstr, since optimizeCmpInstr
         // can enable folding by converting SUB to CMP.
+        // Save FoldAsLoadDefReg because optimizeLoadInstr() resets it and we
+        // need it for markUsesInDebugValueAsUndef().
+        unsigned FoldedReg = FoldAsLoadDefReg;
         MachineInstr *DefMI = 0;
         MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI,
                                                       FoldAsLoadDefReg, DefMI);
@@ -645,6 +652,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
           LocalMIs.insert(FoldMI);
           MI->eraseFromParent();
           DefMI->eraseFromParent();
+          MRI->markUsesInDebugValueAsUndef(FoldedReg);
           ++NumLoadFold;
 
           // MI is replaced with FoldMI.