Don't merge tiny functions.

It's silly to merge functions like these:

define void @foo(i32 %x) {
  ret void
}

define void @bar(i32 %x) {
  ret void
}

to get

define void @bar(i32) {
  tail call void @foo(i32 %0)
  ret void
}

llvm-svn: 191786

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 0f09b9026eb..7e4c1668455 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -836,6 +836,18 @@ bool MergeFunctions::insert(ComparableFunction &NewF) {
 
   const ComparableFunction &OldF = *Result.first;
 
+  // Don't merge tiny functions, since it can just end up making the function
+  // larger.
+  // FIXME: Should still merge them if they are unnamed_addr and produce an
+  // alias.
+  if (NewF.getFunc()->size() == 1) {
+    if (NewF.getFunc()->front().size() <= 2) {
+      DEBUG(dbgs() << NewF.getFunc()->getName()
+            << " is to small to bother merging\n");
+      return false;
+    }
+  }
+
   // Never thunk a strong function to a weak function.
   assert(!OldF.getFunc()->mayBeOverridden() ||
          NewF.getFunc()->mayBeOverridden());