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[CodeGen] Split out cold exception handling pads.

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Support for splitting exception handling pads was added in D73739. This
change updates the code to split out exception handling pads if profile
information indicates that they are cold. For a given function with
multiple landind pads, if one of them is hot they are all retained as
part of the hot code section.

Differential Revision: https://reviews.llvm.org/D96372
This commit is contained in:
Snehasish Kumar 2021-02-09 14:13:47 -08:00
parent b8b6f85b4f
commit 4a5bac2f05
2 changed files with 62 additions and 8 deletions
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25
lib/CodeGen/MachineFunctionSplitter.cpp
View File

@ -23,6 +23,7 @@
// https://groups.google.com/d/msg/llvm-dev/RUegaMg-iqc/wFAVxa6fCgAJ
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/CodeGen/BasicBlockSectionUtils.h"
@ -77,7 +78,7 @@ public:
};
} // end anonymous namespace
static bool isColdBlock(MachineBasicBlock &MBB,
static bool isColdBlock(const MachineBasicBlock &MBB,
const MachineBlockFrequencyInfo *MBFI,
ProfileSummaryInfo *PSI) {
Optional<uint64_t> Count = MBFI->getBlockProfileCount(&MBB);
@ -121,16 +122,28 @@ bool MachineFunctionSplitter::runOnMachineFunction(MachineFunction &MF) {
auto *MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
SmallVector<MachineBasicBlock *, 2> LandingPads;
for (auto &MBB : MF) {
// FIXME: We retain the entry block and conservatively keep all landing pad
// blocks as part of the original function. Once D73739 is submitted, we can
// improve the handling of ehpads.
if ((MBB.pred_empty() || MBB.isEHPad()))
if (MBB.isEntryBlock())
continue;
if (isColdBlock(MBB, MBFI, PSI))
if (MBB.isEHPad())
LandingPads.push_back(&MBB);
else if (isColdBlock(MBB, MBFI, PSI))
MBB.setSectionID(MBBSectionID::ColdSectionID);
}
// We only split out eh pads if all of them are cold.
bool HasHotLandingPads = false;
for (const MachineBasicBlock *LP : LandingPads) {
if (!isColdBlock(*LP, MBFI, PSI))
HasHotLandingPads = true;
}
if (!HasHotLandingPads) {
for (MachineBasicBlock *LP : LandingPads)
LP->setSectionID(MBBSectionID::ColdSectionID);
}
auto Comparator = [](const MachineBasicBlock &X, const MachineBasicBlock &Y) {
return X.getSectionID().Type < Y.getSectionID().Type;
};

45
test/CodeGen/X86/machine-function-splitter.ll
View File

@ -150,12 +150,12 @@ define void @foo6(i1 zeroext %0) nounwind section "nosplit" !prof !14 {
}
define i32 @foo7(i1 zeroext %0) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) !prof !14 {
;; Check that cold ehpads are not split out.
;; Check that a single cold ehpad is split out.
; MFS-DEFAULTS-LABEL: foo7
; MFS-DEFAULTS: .section .text.split.foo7,"ax",@progbits
; MFS-DEFAULTS-NEXT: foo7.cold:
; MFS-DEFAULTS-NOT: callq _Unwind_Resume
; MFS-DEFAULTS: callq baz
; MFS-DEFAULTS: callq _Unwind_Resume@PLT
entry:
invoke void @_Z1fv()
to label %try.cont unwind label %lpad
@ -182,6 +182,47 @@ try.cont:
ret i32 %7
}
define i32 @foo8(i1 zeroext %0) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) !prof !14 {
;; Check that all ehpads are treated as hot if one of them is hot.
; MFS-DEFAULTS-LABEL: foo8
; MFS-DEFAULTS: callq _Unwind_Resume@PLT
; MFS-DEFAULTS: callq _Unwind_Resume@PLT
; MFS-DEFAULTS: .section .text.split.foo8,"ax",@progbits
; MFS-DEFAULTS-NEXT: foo8.cold:
; MFS-DEFAULTS: callq baz
entry:
invoke void @_Z1fv()
to label %try.cont unwind label %lpad1
lpad1:
%1 = landingpad { i8*, i32 }
cleanup
catch i8* bitcast (i8** @_ZTIi to i8*)
resume { i8*, i32 } %1
try.cont:
br i1 %0, label %hot, label %cold, !prof !17
hot:
%2 = call i32 @bar()
invoke void @_Z1fv()
to label %exit unwind label %lpad2, !prof !21
lpad2:
%3 = landingpad { i8*, i32 }
cleanup
catch i8* bitcast (i8** @_ZTIi to i8*)
resume { i8*, i32 } %3
cold:
%4 = call i32 @baz()
br label %exit
exit:
%5 = tail call i32 @qux()
ret i32 %5
}
declare i32 @bar()
declare i32 @baz()
declare i32 @bam()