[PATCH] D15245: Use the inlinehint-threshold for hot callees.

[Easwaran Raman via llvm-commits]

eraman updated this revision to Diff 43180.
eraman added a comment.

1. Use the hint threshold only if it is greater than regular threshold.
2. Added a test case.


Repository:
  rL LLVM

http://reviews.llvm.org/D15245

Files:
  lib/Transforms/IPO/Inliner.cpp
  test/Transforms/Inline/inline-hot-callee.ll

Index: test/Transforms/Inline/inline-hot-callee.ll
===================================================================
--- /dev/null
+++ test/Transforms/Inline/inline-hot-callee.ll
@@ -0,0 +1,39 @@
+; RUN: opt < %s -inline -inline-threshold=0 -inlinehint-threshold=100 -S | FileCheck %s
+
+; This tests that a hot callee gets the (higher) inlinehint-threshold even without
+; inline hints and gets inlined because the cost is less than inlinehint-threshold.
+; A cold callee with identical body does not get inlined because cost exceeds the
+; inline-threshold
+
+define i32 @callee1(i32 %x) !prof !1 {
+  %x1 = add i32 %x, 1
+  %x2 = add i32 %x1, 1
+  %x3 = add i32 %x2, 1
+
+  ret i32 %x3
+}
+
+define i32 @callee2(i32 %x) !prof !2 {
+; CHECK-LABEL: @callee2(
+  %x1 = add i32 %x, 1
+  %x2 = add i32 %x1, 1
+  %x3 = add i32 %x2, 1
+
+  ret i32 %x3
+}
+
+define i32 @caller2(i32 %y1) !prof !2 {
+; CHECK-LABEL: @caller2(
+; CHECK: call i32 @callee2
+; CHECK-NOT: call i32 @callee1
+; CHECK: ret i32 %x3.i
+  %y2 = call i32 @callee2(i32 %y1)
+  %y3 = call i32 @callee1(i32 %y2)
+  ret i32 %y3
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 1, !"MaxFunctionCount", i32 10}
+!1 = !{!"function_entry_count", i64 10}
+!2 = !{!"function_entry_count", i64 1}
+
Index: lib/Transforms/IPO/Inliner.cpp
===================================================================
--- lib/Transforms/IPO/Inliner.cpp
+++ lib/Transforms/IPO/Inliner.cpp
@@ -296,6 +296,17 @@
   if (InlineHint && HintThreshold > Threshold &&
       !Caller->hasFnAttribute(Attribute::MinSize))
     Threshold = HintThreshold;
+  // If profile information is available, use that to prioritize hot functions.
+  // FIXME: The heuristic used here is based on preliminary SPEC tuning and
+  // may not be optimal. Replace this with a well-tuned heuristic based on
+  // *callsite* hotness and not callee hotness.
+  auto EntryCount = Callee->getEntryCount();
+  auto MaxFunctionCount = Callee->getParent()->getMaximumFunctionCount();
+  if (HintThreshold > Threshold && EntryCount && MaxFunctionCount &&
+      EntryCount.getValue() >=
+          (uint64_t)(0.3 * (double)MaxFunctionCount.getValue())) {
+    Threshold = HintThreshold;
+  }
 
   // Listen to the cold attribute when it would decrease the threshold.
   bool ColdCallee = Callee && !Callee->isDeclaration() &&


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