[CodeGen] Avoid handling DBG_VALUE in the LivePhysRegs (addUses,removeDefs,stepForward)

Summary:
This patch prevents DBG_VALUE instructions from influencing
LivePhysRegs::stepBackwards and stepForwards.  In at least one case,
specifically branch folding, the stepBackwards logic was having an
influence on code generation.  The result was that certain code
compiled with '-g -O2' would differ from that compiled with '-O2'
alone. It seems that the original logic, accounting for DBG_VALUE,
was influencing the placement of an IMPLICIT_DEF which had a later
impact on how blocks were processed in branch folding.

Reviewers: kparzysz, MatzeB

Reviewed By: kparzysz

Subscribers: bjope, llvm-commits

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D43850

llvm-svn: 327862

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/LivePhysRegs.cpp b/llvm/lib/CodeGen/LivePhysRegs.cpp
index 277212cf7da..62ff69600c9 100644
--- a/llvm/lib/CodeGen/LivePhysRegs.cpp
+++ b/llvm/lib/CodeGen/LivePhysRegs.cpp
@@ -44,7 +44,7 @@ void LivePhysRegs::removeRegsInMask(const MachineOperand &MO,
 void LivePhysRegs::removeDefs(const MachineInstr &MI) {
   for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
     if (O->isReg()) {
-      if (!O->isDef())
+      if (!O->isDef() || O->isDebug())
         continue;
       unsigned Reg = O->getReg();
       if (!TargetRegisterInfo::isPhysicalRegister(Reg))
@@ -58,7 +58,7 @@ void LivePhysRegs::removeDefs(const MachineInstr &MI) {
 /// Add uses to the set.
 void LivePhysRegs::addUses(const MachineInstr &MI) {
   for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
-    if (!O->isReg() || !O->readsReg())
+    if (!O->isReg() || !O->readsReg() || O->isDebug())
       continue;
     unsigned Reg = O->getReg();
     if (!TargetRegisterInfo::isPhysicalRegister(Reg))
@@ -85,7 +85,7 @@ void LivePhysRegs::stepForward(const MachineInstr &MI,
         SmallVectorImpl<std::pair<unsigned, const MachineOperand*>> &Clobbers) {
   // Remove killed registers from the set.
   for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
-    if (O->isReg()) {
+    if (O->isReg() && !O->isDebug()) {
       unsigned Reg = O->getReg();
       if (!TargetRegisterInfo::isPhysicalRegister(Reg))
         continue;