[PATCH] D34471: [Inliner] Boost inlining of an indirect call to always_inline function.

[Easwaran Raman via Phabricator via llvm-commits]

eraman created this revision.
Herald added a subscriber: mehdi_amini.

If inlining baz->bar makes an indirect call inside bar to be a direct
call to foo with always_inline hint, boost the chances of baz->bar
inlining (and therefore bar->foo inlining) by adding a large negative
cost. I have used LastCallToStaticBonus here, but if that makes it
confusing I will create another constant with similar high value.


https://reviews.llvm.org/D34471

Files:
  lib/Analysis/InlineCost.cpp
  test/Transforms/Inline/inline-indirect-always.ll


Index: test/Transforms/Inline/inline-indirect-always.ll
===================================================================
--- /dev/null
+++ test/Transforms/Inline/inline-indirect-always.ll
@@ -0,0 +1,32 @@
+; RUN: opt -S -inline -inline-threshold=0 < %s | FileCheck %s
+declare void @ext();
+
+define void @foo() #1 {
+  call void @ext();
+  ret void
+}
+
+define  void @bar(void ()* %fptr) {
+  call void %fptr();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  call void @ext();
+  ret void
+}
+; CHECK-LABEL: @baz
+define void @baz() {
+; CHECK-NOT: call void @bar
+  call void @bar(void ()* @foo)
+; CHECK: ret
+  ret void
+}
+
+attributes #1 = { alwaysinline }
Index: lib/Analysis/InlineCost.cpp
===================================================================
--- lib/Analysis/InlineCost.cpp
+++ lib/Analysis/InlineCost.cpp
@@ -970,7 +970,17 @@
   // through it and see the function target. This happens not infrequently
   // during devirtualization and so we want to give it a hefty bonus for
   // inlining, but cap that bonus in the event that inlining wouldn't pan
-  // out. Pretend to inline the function, with a custom threshold.
+  // out.
+
+  // First, check if the function has AlwaysInline attribute and give a huge
+  // bonus if that is the case.
+  if (F->hasFnAttribute(Attribute::AlwaysInline)) {
+    Cost -= InlineConstants::LastCallToStaticBonus;
+    return Base::visitCallSite(CS);
+  }
+
+  // Otherwise, pretend to inline the function, with a custom threshold and give
+  // a bonus based on this threshold and the cost of inlining F.
   auto IndirectCallParams = Params;
   IndirectCallParams.DefaultThreshold = InlineConstants::IndirectCallThreshold;
   CallAnalyzer CA(TTI, GetAssumptionCache, GetBFI, PSI, *F, CS,


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