[ARM] Don't replicate instructions in Ifcvt at minsize

Ifcvt can replicate instructions as it converts them to be predicated. This
stops that from happening on thumb2 targets at minsize where an extra IT
instruction is likely needed.

Differential Revision: https://reviews.llvm.org/D60089

llvm-svn: 358974

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 490bf5fb56c..32c0cbde3cf 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1933,6 +1933,15 @@ isProfitableToIfCvt(MachineBasicBlock &TBB,
   if (!TCycles)
     return false;
 
+  // In thumb code we often end up trading one branch for a IT block, and
+  // if we are cloning the instruction can increase code size. Prevent
+  // blocks with multiple predecesors from being ifcvted to prevent this
+  // cloning.
+  if (Subtarget.isThumb2() && TBB.getParent()->getFunction().hasMinSize()) {
+    if (TBB.pred_size() != 1 || FBB.pred_size() != 1)
+      return false;
+  }
+
   // Attempt to estimate the relative costs of predication versus branching.
   // Here we scale up each component of UnpredCost to avoid precision issue when
   // scaling TCycles/FCycles by Probability.