[llvm] r351623 - [HotColdSplit] Mark inherently cold functions as such
Vedant Kumar via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 18 18:38:47 PST 2019
Author: vedantk
Date: Fri Jan 18 18:38:47 2019
New Revision: 351623
URL: http://llvm.org/viewvc/llvm-project?rev=351623&view=rev
Log:
[HotColdSplit] Mark inherently cold functions as such
If an inherently cold function is found, mark it as cold. For now this
means applying the `cold` and `minsize` attributes.
As a drive-by, revisit and clean up the criteria for considering a
function for splitting. Add tests.
Added:
llvm/trunk/test/Transforms/HotColdSplit/addr-taken.ll
Modified:
llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp
llvm/trunk/test/Transforms/HotColdSplit/X86/do-not-split.ll
llvm/trunk/test/Transforms/HotColdSplit/minsize.ll
Modified: llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp?rev=351623&r1=351622&r2=351623&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp Fri Jan 18 18:38:47 2019
@@ -153,15 +153,19 @@ static bool isProfitableToOutline(const
return false;
}
-/// Mark \p F cold. Return true if it's changed.
-static bool markEntireFunctionCold(Function &F) {
+/// Mark \p F cold. Based on this assumption, also optimize it for minimum size.
+/// Return true if the function is changed.
+static bool markFunctionCold(Function &F) {
assert(!F.hasFnAttribute(Attribute::OptimizeNone) && "Can't mark this cold");
bool Changed = false;
+ if (!F.hasFnAttribute(Attribute::Cold)) {
+ F.addFnAttr(Attribute::Cold);
+ Changed = true;
+ }
if (!F.hasFnAttribute(Attribute::MinSize)) {
F.addFnAttr(Attribute::MinSize);
Changed = true;
}
- // TODO: Move this function into a cold section.
return Changed;
}
@@ -175,6 +179,7 @@ public:
bool run(Module &M);
private:
+ bool isFunctionCold(const Function &F) const;
bool shouldOutlineFrom(const Function &F) const;
bool outlineColdRegions(Function &F, ProfileSummaryInfo &PSI,
BlockFrequencyInfo *BFI, TargetTransformInfo &TTI,
@@ -208,28 +213,29 @@ public:
} // end anonymous namespace
-// Returns false if the function should not be considered for hot-cold split
-// optimization.
-bool HotColdSplitting::shouldOutlineFrom(const Function &F) const {
- if (F.size() <= 2)
- return false;
+/// Check whether \p F is inherently cold.
+bool HotColdSplitting::isFunctionCold(const Function &F) const {
+ if (F.hasFnAttribute(Attribute::Cold))
+ return true;
+
+ if (F.getCallingConv() == CallingConv::Cold)
+ return true;
- // TODO: Consider only skipping functions marked `optnone` or `cold`.
+ if (PSI->isFunctionEntryCold(&F))
+ return true;
- if (F.hasAddressTaken())
- return false;
+ return false;
+}
+// Returns false if the function should not be considered for hot-cold split
+// optimization.
+bool HotColdSplitting::shouldOutlineFrom(const Function &F) const {
if (F.hasFnAttribute(Attribute::AlwaysInline))
return false;
if (F.hasFnAttribute(Attribute::NoInline))
return false;
- if (F.getCallingConv() == CallingConv::Cold)
- return false;
-
- if (PSI->isFunctionEntryCold(&F))
- return false;
return true;
}
@@ -259,9 +265,7 @@ Function *HotColdSplitting::extractColdR
}
CI->setIsNoInline();
- // Try to make the outlined code as small as possible on the assumption
- // that it's cold.
- markEntireFunctionCold(*OutF);
+ markFunctionCold(*OutF);
LLVM_DEBUG(llvm::dbgs() << "Outlined Region: " << *OutF);
ORE.emit([&]() {
@@ -492,7 +496,7 @@ bool HotColdSplitting::outlineColdRegion
if (Region.isEntireFunctionCold()) {
LLVM_DEBUG(dbgs() << "Entire function is cold\n");
- return markEntireFunctionCold(F);
+ return markFunctionCold(F);
}
// If this outlining region intersects with another, drop the new region.
@@ -548,10 +552,25 @@ bool HotColdSplitting::run(Module &M) {
for (auto It = M.begin(), End = M.end(); It != End; ++It) {
Function &F = *It;
+ // Do not touch declarations.
+ if (F.isDeclaration())
+ continue;
+
+ // Do not modify `optnone` functions.
+ if (F.hasFnAttribute(Attribute::OptimizeNone))
+ continue;
+
+ // Detect inherently cold functions and mark them as such.
+ if (isFunctionCold(F)) {
+ Changed |= markFunctionCold(F);
+ continue;
+ }
+
if (!shouldOutlineFrom(F)) {
LLVM_DEBUG(llvm::dbgs() << "Skipping " << F.getName() << "\n");
continue;
}
+
LLVM_DEBUG(llvm::dbgs() << "Outlining in " << F.getName() << "\n");
DominatorTree DT(F);
PostDomTree PDT(F);
Modified: llvm/trunk/test/Transforms/HotColdSplit/X86/do-not-split.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/HotColdSplit/X86/do-not-split.ll?rev=351623&r1=351622&r2=351623&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/HotColdSplit/X86/do-not-split.ll (original)
+++ llvm/trunk/test/Transforms/HotColdSplit/X86/do-not-split.ll Fri Jan 18 18:38:47 2019
@@ -43,6 +43,37 @@ entry:
br i1 undef, label %if.then, label %if.end
if.then: ; preds = %entry
+ call void @sink()
+ br label %if.end
+
+if.end: ; preds = %entry
+ ret void
+}
+
+; Do not split `noinline` functions.
+; CHECK-LABEL: @noinline_func
+; CHECK-NOT: noinline_func.cold.1
+define void @noinline_func() noinline {
+entry:
+ br i1 undef, label %if.then, label %if.end
+
+if.then: ; preds = %entry
+ call void @sink()
+ br label %if.end
+
+if.end: ; preds = %entry
+ ret void
+}
+
+; Do not split `alwaysinline` functions.
+; CHECK-LABEL: @alwaysinline_func
+; CHECK-NOT: alwaysinline_func.cold.1
+define void @alwaysinline_func() alwaysinline {
+entry:
+ br i1 undef, label %if.then, label %if.end
+
+if.then: ; preds = %entry
+ call void @sink()
br label %if.end
if.end: ; preds = %entry
Added: llvm/trunk/test/Transforms/HotColdSplit/addr-taken.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/HotColdSplit/addr-taken.ll?rev=351623&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/HotColdSplit/addr-taken.ll (added)
+++ llvm/trunk/test/Transforms/HotColdSplit/addr-taken.ll Fri Jan 18 18:38:47 2019
@@ -0,0 +1,27 @@
+; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=0 -S < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+; CHECK: define {{.*}} @foo{{.*}}#[[outlined_func_attr:[0-9]+]]
+define void @foo() noreturn cold {
+ unreachable
+}
+
+; CHECK: define {{.*}} @bar.cold.1{{.*}}#[[outlined_func_attr]]
+define void @bar() {
+ br i1 undef, label %normal, label %exit
+
+normal:
+ unreachable
+
+exit:
+ ret void
+}
+
+ at take_addr_of_foo = global void ()* @foo
+ at take_addr_of_bar = global void ()* @bar
+
+; CHECK: attributes #[[outlined_func_attr]] = {
+; CHECK-SAME: cold
+; CHECK-SAME: minsize
Modified: llvm/trunk/test/Transforms/HotColdSplit/minsize.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/HotColdSplit/minsize.ll?rev=351623&r1=351622&r2=351623&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/HotColdSplit/minsize.ll (original)
+++ llvm/trunk/test/Transforms/HotColdSplit/minsize.ll Fri Jan 18 18:38:47 2019
@@ -17,7 +17,15 @@ if.else:
ret void
}
+; CHECK: define {{.*}} @foo{{.*}}#[[outlined_func_attr:[0-9]+]]
+define void @foo() cold {
+ ret void
+}
+
declare void @sink() cold
-; CHECK: define {{.*}} @fun.cold.1{{.*}}#[[outlined_func_attr:[0-9]+]]
-; CHECK: attributes #[[outlined_func_attr]] = { {{.*}}minsize
+; CHECK: define {{.*}} @fun.cold.1{{.*}}#[[outlined_func_attr]]
+
+; CHECK: attributes #[[outlined_func_attr]] = {
+; CHECK-SAME: cold
+; CHECK-SAME: minsize
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