Stabilize the order of live intervals in the priority_queue used by the

linear scan reg alloc.  This fixes a problem I ran into where extracting
a function from a larger file caused the generated code to change (masking
the problem I was trying to debug) because the allocator behaved differently.

This changes the results for two X86 regression checks.  stack-color-with-reg
is improved, with one less instruction, but pr3495 is worse, with one more
copy.  As far as I can tell, these tests were just getting lucky or unlucky,
so I've changed the expected results.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81060 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 1 deletions

diff --git a/include/llvm/CodeGen/LiveInterval.h b/include/llvm/CodeGen/LiveInterval.h
index 921c5572b9..2a8c2c8841 100644
--- a/include/llvm/CodeGen/LiveInterval.h
+++ b/include/llvm/CodeGen/LiveInterval.h
@@ -774,7 +774,10 @@ namespace llvm {
     void ComputeJoinedWeight(const LiveInterval &Other);
 
     bool operator<(const LiveInterval& other) const {
-      return beginIndex() < other.beginIndex();
+      const MachineInstrIndex &thisIndex = beginIndex();
+      const MachineInstrIndex &otherIndex = other.beginIndex();
+      return (thisIndex < otherIndex ||
+              (thisIndex == otherIndex && reg < other.reg));
     }
 
     void print(raw_ostream &OS, const TargetRegisterInfo *TRI = 0) const;