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[CodeGen] Add an option to skip extTSP BB placement for huge functions. #99310

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Jul 24, 2024
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[CodeGen] Add an option to skip extTSP BB placement for huge functions. #99310

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9 changes: 8 additions & 1 deletion llvm/lib/CodeGen/MachineBlockPlacement.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -213,6 +213,12 @@ static cl::opt<bool> RenumberBlocksBeforeView(
"into a dot graph. Only used when a function is being printed."),
cl::init(false), cl::Hidden);

static cl::opt<unsigned> ExtTspBlockPlacementMaxBlocks(
"ext-tsp-block-placement-max-blocks",
cl::desc("Maximum number of basic blocks in a function to run ext-TSP "
"block placement."),
cl::init(UINT_MAX), cl::Hidden);

namespace llvm {
extern cl::opt<bool> EnableExtTspBlockPlacement;
extern cl::opt<bool> ApplyExtTspWithoutProfile;
Expand Down Expand Up @@ -3511,7 +3517,8 @@ bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &MF) {

// Apply a post-processing optimizing block placement.
if (MF.size() >= 3 && EnableExtTspBlockPlacement &&
(ApplyExtTspWithoutProfile || MF.getFunction().hasProfileData())) {
(ApplyExtTspWithoutProfile || MF.getFunction().hasProfileData()) &&
MF.size() <= ExtTspBlockPlacementMaxBlocks) {
// Find a new placement and modify the layout of the blocks in the function.
applyExtTsp();

Expand Down
15 changes: 15 additions & 0 deletions llvm/test/CodeGen/X86/code_placement_ext_tsp_large.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux -enable-ext-tsp-block-placement=1 -ext-tsp-chain-split-threshold=128 -debug-only=block-placement < %s 2>&1 | FileCheck %s
; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux -enable-ext-tsp-block-placement=1 -ext-tsp-chain-split-threshold=1 -debug-only=block-placement < %s 2>&1 | FileCheck %s -check-prefix=CHECK2
; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux -enable-ext-tsp-block-placement=0 -debug-only=block-placement < %s 2>&1 | FileCheck %s -check-prefix=CHECK3
; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux -enable-ext-tsp-block-placement=1 -ext-tsp-block-placement-max-blocks=8 -debug-only=block-placement < %s 2>&1 | FileCheck %s -check-prefix=CHECK4

@yydebug = dso_local global i32 0, align 4

Expand Down Expand Up @@ -110,6 +111,20 @@ define void @func_large() !prof !0 {
; CHECK3: b7
; CHECK3: b8
; CHECK3: b9
;
; An expected output with function size larger than the threshold -- the layout is not modified:
;
; CHECK4-LABEL: func_large:
; CHECK4: b0
; CHECK4: b1
; CHECK4: b2
; CHECK4: b3
; CHECK4: b4
; CHECK4: b5
; CHECK4: b6
; CHECK4: b7
; CHECK4: b8
; CHECK4: b9

b0:
%0 = load i32, ptr @yydebug, align 4
Expand Down
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