[AMDGPU] Fix read-undef flags when schedule is reverted

If two subregs of the same register are defined and we need to revert
schedule changing def order, we will end up with both instructions
having def,read-undef flags because adjustLaneLiveness() will only set
this flag but will not remove it.

Fix this by removing read-undef flags before calling adjustLaneLiveness.

Differential Revision: https://reviews.llvm.org/D30428

1 files changed, 15 insertions, 12 deletions

diff --git a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
index 91034030f6e..6d4ee217cf1 100644
--- a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
@@ -348,19 +348,22 @@ void GCNScheduleDAGMILive::schedule() {
     if (MI->getIterator() != RegionEnd) {
       BB->remove(MI);
       BB->insert(RegionEnd, MI);
-      if (LIS) {
+      if (LIS)
         LIS->handleMove(*MI, true);
-        RegisterOperands RegOpers;
-        RegOpers.collect(*MI, *TRI, MRI, ShouldTrackLaneMasks, false);
-        if (ShouldTrackLaneMasks) {
-          // Adjust liveness and add missing dead+read-undef flags.
-          SlotIndex SlotIdx = LIS->getInstructionIndex(*MI).getRegSlot();
-          RegOpers.adjustLaneLiveness(*LIS, MRI, SlotIdx, MI);
-        } else {
-          // Adjust for missing dead-def flags.
-          RegOpers.detectDeadDefs(*MI, *LIS);
-        }
-      }
+    }
+    // Reset read-undef flags and update them later.
+    for (auto &Op : MI->operands())
+      if (Op.isReg() && Op.isDef())
+        Op.setIsUndef(false);
+    RegisterOperands RegOpers;
+    RegOpers.collect(*MI, *TRI, MRI, ShouldTrackLaneMasks, false);
+    if (ShouldTrackLaneMasks) {
+      // Adjust liveness and add missing dead+read-undef flags.
+      SlotIndex SlotIdx = LIS->getInstructionIndex(*MI).getRegSlot();
+      RegOpers.adjustLaneLiveness(*LIS, MRI, SlotIdx, MI);
+    } else {
+      // Adjust for missing dead-def flags.
+      RegOpers.detectDeadDefs(*MI, *LIS);
     }
     RegionEnd = MI->getIterator();
     ++RegionEnd;