[llvm] 4bdc938 - [CSSPGO][Preinliner] Always inline zero-sized functions.

[Hongtao Yu via llvm-commits]

Author: Hongtao Yu
Date: 2023-06-27T17:06:24-07:00
New Revision: 4bdc938ce3f0bc7721d1942b23cd49734121094a

URL: https://github.com/llvm/llvm-project/commit/4bdc938ce3f0bc7721d1942b23cd49734121094a
DIFF: https://github.com/llvm/llvm-project/commit/4bdc938ce3f0bc7721d1942b23cd49734121094a.diff

LOG: [CSSPGO][Preinliner] Always inline zero-sized functions.

Zero-sized functions should be cost-free in term of size budget, so they should be considered during inlining even if we run out of size budget.

This appears to give 0.5% win for one of our internal services.

Reviewed By: wenlei

Differential Revision: https://reviews.llvm.org/D153820

Added: 
    

Modified: 
    llvm/tools/llvm-profgen/CSPreInliner.h

Removed: 
    


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diff  --git a/llvm/tools/llvm-profgen/CSPreInliner.h b/llvm/tools/llvm-profgen/CSPreInliner.h
index 09dd2dec1149c..4d848aafdab91 100644
--- a/llvm/tools/llvm-profgen/CSPreInliner.h
+++ b/llvm/tools/llvm-profgen/CSPreInliner.h
@@ -41,6 +41,13 @@ struct ProfiledInlineCandidate {
 struct ProfiledCandidateComparer {
   bool operator()(const ProfiledInlineCandidate &LHS,
                   const ProfiledInlineCandidate &RHS) {
+    // Always prioritize inlining zero-sized functions as they do not affect the
+    // size budget. This could happen when all of the callee's code is gone and
+    // only pseudo probes are left.
+    if ((LHS.SizeCost == 0 || RHS.SizeCost == 0) &&
+        (LHS.SizeCost != RHS.SizeCost))
+      return RHS.SizeCost == 0;
+
     if (LHS.CallsiteCount != RHS.CallsiteCount)
       return LHS.CallsiteCount < RHS.CallsiteCount;