For now, avoid commuting def MI for copy MI's whose source is not killed. That simply trade a live interval for another and because only the non-two-address operands can be folded into loads, may end up pessimising code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47262 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 17a8908..199c89e 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -247,6 +247,13 @@ bool SimpleRegisterCoalescing::RemoveCopyByCommutingDef(LiveInterval &IntA,
 
   unsigned CopyIdx = li_->getDefIndex(li_->getInstructionIndex(CopyMI));
 
+  // FIXME: For now, only eliminate the copy by commuting its def is the source
+  // does not live pass the move. Coalescing those copies may end up may simply
+  // end up swapping a live interval for another. That and because usually only
+  // the non-two address operand can be folded can end up pessimizing the code.
+  if (CopyMI->findRegisterUseOperandIdx(IntA.reg, true) != -1)
+    return false;
+
   // BValNo is a value number in B that is defined by a copy from A. 'B3' in
   // the example above.
   LiveInterval::iterator BLR = IntB.FindLiveRangeContaining(CopyIdx);