Treat indirect branches specially only during pre-regalloc tail duplication,
not during the later post-alloc tail duplication.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93600 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp
index a2af8b3..d6860bc 100644
--- a/lib/CodeGen/TailDuplication.cpp
+++ b/lib/CodeGen/TailDuplication.cpp
@@ -433,29 +433,29 @@
TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallVector<MachineInstr*, 16> &Copies) {
- // Pre-regalloc tail duplication hurts compile time and doesn't help
- // much except for indirect branches.
- bool hasIndirectBranch = (!TailBB->empty() &&
- TailBB->back().getDesc().isIndirectBranch());
- if (PreRegAlloc && !hasIndirectBranch)
- return false;
-
// Set the limit on the number of instructions to duplicate, with a default
// of one less than the tail-merge threshold. When optimizing for size,
// duplicate only one, because one branch instruction can be eliminated to
// compensate for the duplication.
unsigned MaxDuplicateCount;
- if (hasIndirectBranch)
- // If the target has hardware branch prediction that can handle indirect
- // branches, duplicating them can often make them predictable when there
- // are common paths through the code. The limit needs to be high enough
- // to allow undoing the effects of tail merging.
- MaxDuplicateCount = 20;
- else if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
+ if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
MaxDuplicateCount = 1;
else
MaxDuplicateCount = TailDuplicateSize;
+ if (PreRegAlloc) {
+ // Pre-regalloc tail duplication hurts compile time and doesn't help
+ // much except for indirect branches.
+ if (TailBB->empty() || !TailBB->back().getDesc().isIndirectBranch())
+ return false;
+ // If the target has hardware branch prediction that can handle indirect
+ // branches, duplicating them can often make them predictable when there
+ // are common paths through the code. The limit needs to be high enough
+ // to allow undoing the effects of tail merging and other optimizations
+ // that rearrange the predecessors of the indirect branch.
+ MaxDuplicateCount = 20;
+ }
+
// Don't try to tail-duplicate single-block loops.
if (TailBB->isSuccessor(TailBB))
return false;