Decrease inlinecold-threshold to 45

[eraman]

Summary

I ran the test-suite (including SPEC 2006) in PGO mode comparing cold thresholds of 225 and 45. Here are some stats on the text size:

Out of 904 tests that ran, 197 see a change in text size. The average text size reduction (of all the 904 binaries) is 1.07%. Of the 197 binaries, 19 see a text size increase, as high as 18%, but most of them are small single source benchmarks. There are 3 multisource benchmarks with a >0.5% size increase (0.7, 1.3 and 2.1 are their % increases). On the other side of the spectrum, 31 benchmarks see >10% size reduction and 6 of them are MultiSource.

I haven't run the test-suite with other values of inlinecold-threshold. Since we have a cold callsite threshold of 45, I picked this value.

[chandlerc]

This seems like a strict improvement to me. I'd love to have a more thorough analysis of different values here but I don't see any reason to hold up bringing this in line with the cold callsite threshold. LGTM.

lib/Analysis/InlineCost.cpp

static cl::opt<bool>
     EnableGenericSwitchCost("inline-generic-switch-cost", cl::Hidden,
                             cl::init(false),
                             cl::desc("Enable generic switch cost model"));
 
 // We introduce this threshold to help performance of instrumentation based
 // PGO before we actually hook up inliner with analysis passes such as BPI and
 // BFI.
 static cl::opt<int> ColdThreshold(
-    "inlinecold-threshold", cl::Hidden, cl::init(225),
+    "inlinecold-threshold", cl::Hidden, cl::init(45),
     cl::desc("Threshold for inlining functions with cold attribute"));
 
 static cl::opt<int>
     HotCallSiteThreshold("hot-callsite-threshold", cl::Hidden, cl::init(3000),
                          cl::ZeroOrMore,
                          cl::desc("Threshold for hot callsites "));
 
 namespace {

test/Transforms/Inline/inline-cold.ll

-; RUN: opt < %s -inline -S -inlinecold-threshold=75 | FileCheck %s
+; RUN: opt < %s -inline -S -inlinecold-threshold=25 | FileCheck %s
 ; Test that functions with attribute Cold are not inlined while the 
 ; same function without attribute Cold will be inlined.
 
 ; RUN: opt < %s -inline -S -inline-threshold=600 | FileCheck %s -check-prefix=OVERRIDE
 ; The command line argument for inline-threshold should override
 ; the default cold threshold, so a cold function with size bigger
 ; than the default cold threshold (225) will be inlined.
 
entry:
   %a1 = load volatile i32, i32* @a
   %x1 = add i32 %a1,  %a1
   %a2 = load volatile i32, i32* @a
   %x2 = add i32 %x1, %a2
   %a3 = load volatile i32, i32* @a
   %x3 = add i32 %x2, %a3
   %a4 = load volatile i32, i32* @a
   %x4 = add i32 %x3, %a4
-  %a5 = load volatile i32, i32* @a
-  %x5 = add i32 %x4, %a5
-  %a6 = load volatile i32, i32* @a
-  %x6 = add i32 %x5, %a6
-  %a7 = load volatile i32, i32* @a
-  %x7 = add i32 %x6, %a6
-  %a8 = load volatile i32, i32* @a
-  %x8 = add i32 %x7, %a8
-  %a9 = load volatile i32, i32* @a
-  %x9 = add i32 %x8, %a9
-  %a10 = load volatile i32, i32* @a
-  %x10 = add i32 %x9, %a10
-  %a11 = load volatile i32, i32* @a
-  %x11 = add i32 %x10, %a11
-  %a12 = load volatile i32, i32* @a
-  %x12 = add i32 %x11, %a12
-  %add = add i32 %x12, %a
+  %add = add i32 %x4, %a
   ret i32 %add
 }
 
 ; This function should be larger than the default cold threshold (225).
 define i32 @ColdFunction2(i32 %a) #1 {
 ; CHECK-LABEL: @ColdFunction2
 ; CHECK: ret
 ; OVERRIDE-LABEL: @ColdFunction2