[llvm] [FuncSpec] Update MinFunctionSize logic (PR #112711)

[Hari Limaye via llvm-commits]

https://github.com/hazzlim created https://github.com/llvm/llvm-project/pull/112711

Always require functions to be larger than MinFunctionSize when SpecializeLiteralConstant is enabled, and increase MinFunctionSize to 400, to prevent excessive triggering of specialisations on small functions.

>From 202896165ac0012bf2d08b13d84eb4ccfbd234af Mon Sep 17 00:00:00 2001
From: Hari Limaye <hari.limaye at arm.com>
Date: Thu, 17 Oct 2024 10:21:37 +0000
Subject: [PATCH] [FuncSpec] Update MinFunctionSize logic

Always require functions to be larger than MinFunctionSize when
SpecializeLiteralConstant is enabled, and increase MinFunctionSize to
400, to prevent excessive triggering of specialisations on small
functions.
---
 .../lib/Transforms/IPO/FunctionSpecialization.cpp | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
index bd0a337e579e48..6d5c8b4229a417 100644
--- a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -57,9 +57,9 @@ static cl::opt<unsigned> MaxBlockPredecessors(
     "considered during the estimation of dead code"));
 
 static cl::opt<unsigned> MinFunctionSize(
-    "funcspec-min-function-size", cl::init(300), cl::Hidden, cl::desc(
-    "Don't specialize functions that have less than this number of "
-    "instructions"));
+    "funcspec-min-function-size", cl::init(500), cl::Hidden,
+    cl::desc("Don't specialize functions that have less than this number of "
+             "instructions"));
 
 static cl::opt<unsigned> MaxCodeSizeGrowth(
     "funcspec-max-codesize-growth", cl::init(3), cl::Hidden, cl::desc(
@@ -641,12 +641,17 @@ bool FunctionSpecializer::run() {
         Metrics.analyzeBasicBlock(&BB, GetTTI(F), EphValues);
     }
 
+    // When specializing literal constants is enabled, always require functions
+    // to be larger than MinFunctionSize, to prevent excessive specialization.
+    bool RequireMinSize =
+        !ForceSpecialization &&
+        (SpecializeLiteralConstant || !F.hasFnAttribute(Attribute::NoInline));
+
     // If the code metrics reveal that we shouldn't duplicate the function,
     // or if the code size implies that this function is easy to get inlined,
     // then we shouldn't specialize it.
     if (Metrics.notDuplicatable || !Metrics.NumInsts.isValid() ||
-        (!ForceSpecialization && !F.hasFnAttribute(Attribute::NoInline) &&
-         Metrics.NumInsts < MinFunctionSize))
+        (RequireMinSize && Metrics.NumInsts < MinFunctionSize))
       continue;
 
     // TODO: For now only consider recursive functions when running multiple