EXPERIMENT only fold subreg operands when they aren't used often

1 files changed, 12 insertions, 3 deletions

diff --git a/lib/Target/AMDGPU/SIFoldOperands.cpp b/lib/Target/AMDGPU/SIFoldOperands.cpp
index ccbf7c80f2a..68eb3ccd36b 100644
--- a/lib/Target/AMDGPU/SIFoldOperands.cpp
+++ b/lib/Target/AMDGPU/SIFoldOperands.cpp
@@ -334,9 +334,18 @@ bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
           !MRI.hasOneUse(MI.getOperand(0).getReg()))
         continue;
 
-      if (OpToFold.isReg() &&
-          !TargetRegisterInfo::isVirtualRegister(OpToFold.getReg()))
-        continue;
+      if (OpToFold.isReg()) {
+        if (!TargetRegisterInfo::isVirtualRegister(OpToFold.getReg()))
+          continue;
+
+        if (OpToFold.getSubReg()) {
+          unsigned Uses = 0;
+          for (auto UI = MRI.use_begin(MI.getOperand(0).getReg()); UI != MRI.use_end() && Uses <= 2; ++UI)
+            ++Uses;
+          if (Uses > 2)
+            continue;
+        }
+      }
 
       // We need mutate the operands of new mov instructions to add implicit
       // uses of EXEC, but adding them invalidates the use_iterator, so defer