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Backport MergeFunctions scheduling fix #123

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Merged
merged 2 commits into from
Dec 8, 2021
Merged

Backport MergeFunctions scheduling fix #123

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e1b02f2
[PhaseOrdering] Add test for incorrect merge function scheduling
nikic Dec 3, 2021
4d82dca
[NewPM] Fix MergeFunctions scheduling
nikic Dec 4, 2021
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40 changes: 22 additions & 18 deletions llvm/lib/Passes/PassBuilder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -278,6 +278,10 @@ static cl::opt<bool> EnableO3NonTrivialUnswitching(
"enable-npm-O3-nontrivial-unswitch", cl::init(true), cl::Hidden,
cl::ZeroOrMore, cl::desc("Enable non-trivial loop unswitching for -O3"));

static cl::opt<bool> EnableMergeFunctions(
"enable-merge-functions", cl::init(false), cl::Hidden,
cl::desc("Enable function merging as part of the optimization pipeline"));

PipelineTuningOptions::PipelineTuningOptions() {
LoopInterleaving = true;
LoopVectorization = true;
Expand All @@ -287,7 +291,7 @@ PipelineTuningOptions::PipelineTuningOptions() {
LicmMssaOptCap = SetLicmMssaOptCap;
LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap;
CallGraphProfile = true;
MergeFunctions = false;
MergeFunctions = EnableMergeFunctions;
}

namespace llvm {
Expand Down Expand Up @@ -1416,23 +1420,6 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,

addVectorPasses(Level, OptimizePM, /* IsFullLTO */ false);

// Split out cold code. Splitting is done late to avoid hiding context from
// other optimizations and inadvertently regressing performance. The tradeoff
// is that this has a higher code size cost than splitting early.
if (EnableHotColdSplit && !LTOPreLink)
MPM.addPass(HotColdSplittingPass());

// Search the code for similar regions of code. If enough similar regions can
// be found where extracting the regions into their own function will decrease
// the size of the program, we extract the regions, a deduplicate the
// structurally similar regions.
if (EnableIROutliner)
MPM.addPass(IROutlinerPass());

// Merge functions if requested.
if (PTO.MergeFunctions)
MPM.addPass(MergeFunctionsPass());

// LoopSink pass sinks instructions hoisted by LICM, which serves as a
// canonicalization pass that enables other optimizations. As a result,
// LoopSink pass needs to be a very late IR pass to avoid undoing LICM
Expand All @@ -1459,6 +1446,23 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
for (auto &C : OptimizerLastEPCallbacks)
C(MPM, Level);

// Split out cold code. Splitting is done late to avoid hiding context from
// other optimizations and inadvertently regressing performance. The tradeoff
// is that this has a higher code size cost than splitting early.
if (EnableHotColdSplit && !LTOPreLink)
MPM.addPass(HotColdSplittingPass());

// Search the code for similar regions of code. If enough similar regions can
// be found where extracting the regions into their own function will decrease
// the size of the program, we extract the regions, a deduplicate the
// structurally similar regions.
if (EnableIROutliner)
MPM.addPass(IROutlinerPass());

// Merge functions if requested.
if (PTO.MergeFunctions)
MPM.addPass(MergeFunctionsPass());

if (PTO.CallGraphProfile)
MPM.addPass(CGProfilePass());

Expand Down
119 changes: 119 additions & 0 deletions llvm/test/Transforms/PhaseOrdering/X86/merge-functions.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,119 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes='default<O3>' -enable-merge-functions -S < %s | FileCheck %s

; TODO: These two functions should get merged, but currently aren't, because
; the function merging pass is scheduled too early.

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define i1 @test1(i32 %c) {
; CHECK-LABEL: @test1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = add i32 [[C:%.*]], -100
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i32 [[SWITCH_TABLEIDX]], 20
; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i32 [[SWITCH_TABLEIDX]] to i20
; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i20 -490991, [[SWITCH_CAST]]
; CHECK-NEXT: [[TMP1:%.*]] = and i20 [[SWITCH_DOWNSHIFT]], 1
; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = icmp ne i20 [[TMP1]], 0
; CHECK-NEXT: [[I_0:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_MASKED]], i1 false
; CHECK-NEXT: ret i1 [[I_0]]
;
entry:
%_4 = alloca i8, align 1
%_3 = alloca i8, align 1
%_2 = alloca i8, align 1
%i = alloca i8, align 1
%i1 = icmp eq i32 %c, 115
br i1 %i1, label %bb10, label %bb11

bb10: ; preds = %entry
store i8 1, i8* %_4, align 1
br label %bb12

bb11: ; preds = %entry
%_6 = icmp eq i32 %c, 109
%i2 = zext i1 %_6 to i8
store i8 %i2, i8* %_4, align 1
br label %bb12

bb12: ; preds = %bb11, %bb10
%i3 = load i8, i8* %_4, align 1
%i4 = trunc i8 %i3 to i1
br i1 %i4, label %bb7, label %bb8

bb8: ; preds = %bb12
%_8 = icmp eq i32 %c, 104
%i5 = zext i1 %_8 to i8
store i8 %i5, i8* %_3, align 1
br label %bb9

bb7: ; preds = %bb12
store i8 1, i8* %_3, align 1
br label %bb9

bb9: ; preds = %bb7, %bb8
%i6 = load i8, i8* %_3, align 1
%i7 = trunc i8 %i6 to i1
br i1 %i7, label %bb4, label %bb5

bb5: ; preds = %bb9
%_10 = icmp eq i32 %c, 100
%i8 = zext i1 %_10 to i8
store i8 %i8, i8* %_2, align 1
br label %bb6

bb4: ; preds = %bb9
store i8 1, i8* %_2, align 1
br label %bb6

bb6: ; preds = %bb4, %bb5
%i9 = load i8, i8* %_2, align 1
%i10 = trunc i8 %i9 to i1
br i1 %i10, label %bb1, label %bb2

bb2: ; preds = %bb6
%_12 = icmp eq i32 %c, 119
%i11 = zext i1 %_12 to i8
store i8 %i11, i8* %i, align 1
br label %bb3

bb1: ; preds = %bb6
store i8 1, i8* %i, align 1
br label %bb3

bb3: ; preds = %bb1, %bb2
%i12 = load i8, i8* %i, align 1
%i13 = trunc i8 %i12 to i1
ret i1 %i13
}

define i1 @test2(i32 %c) {
; CHECK-LABEL: @test2(
; CHECK-NEXT: [[TMP2:%.*]] = tail call i1 @test1(i32 [[TMP0:%.*]]) #[[ATTR0:[0-9]+]]
; CHECK-NEXT: ret i1 [[TMP2]]
;
entry:
%i = alloca i8, align 1
switch i32 %c, label %bb1 [
i32 115, label %bb2
i32 109, label %bb2
i32 104, label %bb2
i32 100, label %bb2
i32 119, label %bb2
]

bb1: ; preds = %entry
store i8 0, i8* %i, align 1
br label %bb3

bb2: ; preds = %entry, %entry, %entry, %entry, %entry
store i8 1, i8* %i, align 1
br label %bb3

bb3: ; preds = %bb2, %bb1
%i1 = load i8, i8* %i, align 1
%i2 = trunc i8 %i1 to i1
ret i1 %i2
}