[llvm] [LLVM] Add HasFakeUses to MachineFunction (PR #110097)
Stephen Tozer via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 26 02:37:38 PDT 2024
https://github.com/SLTozer created https://github.com/llvm/llvm-project/pull/110097
Following the addition of the llvm.fake.use intrinsic and corresponding MIR instruction, two further changes are planned: to add an -fextend-lifetimes flag to Clang that emits these intrinsics, and to have -Og enable this flag by default. Currently, some logic for handling fake uses is gated by the optdebug attribute, which is intended to be switched on by -fextend-lifetimes (and by extension -Og later on). However, the decision was made that a general optdebug attribute should be incompatible with other opt_ attributes (e.g. optsize, optnone), since they all express different intents for how to optimize the program. We would still like to allow -fextend-lifetimes with optsize however (i.e. -Os -fextend-lifetimes should be legal), since it may be a useful configuration and there is no technical reason to not allow it.
This patch resolves this by tracking MachineFunctions that have fake uses, allowing us to run passes that interact with them and skip passes that clash with them.
>From eabb3d0ff5549b4109cee688da3f22d5604623cb Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Thu, 26 Sep 2024 10:16:29 +0100
Subject: [PATCH] [LLVM] Add HasFakeUses to MachineFunction
Following the addition of the llvm.fake.use intrinsic and corresponding MIR
instruction, two further changes are planned: to add an -fextend-lifetimes flag
to Clang that emits these intrinsics, and to have -Og enable this flag by
default. Currently, some logic for handling fake uses is gated by the optdebug
attribute, which is intended to be switched on by -fextend-lifetimes (and by
extension -Og later on). However, the decision was made that a general optdebug
attribute should be incompatible with other opt_ attributes (e.g. optsize,
optnone), since they all express different intents for how to optimize the
program. We would still like to allow -fextend-lifetimes with optsize however
(i.e. -Os -fextend-lifetimes should be legal), since it may be a useful
configuration and there is no technical reason to not allow it.
---
llvm/include/llvm/CodeGen/MIRYamlMapping.h | 2 +
llvm/include/llvm/CodeGen/MachineFunction.h | 4 ++
llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp | 1 +
llvm/lib/CodeGen/MIRParser/MIRParser.cpp | 1 +
llvm/lib/CodeGen/MIRPrinter.cpp | 1 +
llvm/lib/CodeGen/MachineScheduler.cpp | 2 +-
llvm/lib/CodeGen/PostRASchedulerList.cpp | 2 +-
llvm/lib/CodeGen/RemoveLoadsIntoFakeUses.cpp | 6 +-
.../SelectionDAG/FunctionLoweringInfo.cpp | 11 +++-
.../CodeGen/X86/fake-use-postra-scheduler.mir | 55 +++++++++++++++++++
.../llvm-reduce/mir/preserve-func-info.mir | 2 +
llvm/tools/llvm-reduce/ReducerWorkItem.cpp | 1 +
12 files changed, 79 insertions(+), 9 deletions(-)
create mode 100644 llvm/test/CodeGen/X86/fake-use-postra-scheduler.mir
diff --git a/llvm/include/llvm/CodeGen/MIRYamlMapping.h b/llvm/include/llvm/CodeGen/MIRYamlMapping.h
index ab8dc442e04b7b..db052dffa93cbc 100644
--- a/llvm/include/llvm/CodeGen/MIRYamlMapping.h
+++ b/llvm/include/llvm/CodeGen/MIRYamlMapping.h
@@ -740,6 +740,7 @@ struct MachineFunction {
bool HasEHCatchret = false;
bool HasEHScopes = false;
bool HasEHFunclets = false;
+ bool HasFakeUses = false;
bool IsOutlined = false;
bool FailsVerification = false;
@@ -786,6 +787,7 @@ template <> struct MappingTraits<MachineFunction> {
YamlIO.mapOptional("hasEHCatchret", MF.HasEHCatchret, false);
YamlIO.mapOptional("hasEHScopes", MF.HasEHScopes, false);
YamlIO.mapOptional("hasEHFunclets", MF.HasEHFunclets, false);
+ YamlIO.mapOptional("hasFakeUses", MF.HasFakeUses, false);
YamlIO.mapOptional("isOutlined", MF.IsOutlined, false);
YamlIO.mapOptional("debugInstrRef", MF.UseDebugInstrRef, false);
diff --git a/llvm/include/llvm/CodeGen/MachineFunction.h b/llvm/include/llvm/CodeGen/MachineFunction.h
index 5c1da4fa762e84..81589246f7b5da 100644
--- a/llvm/include/llvm/CodeGen/MachineFunction.h
+++ b/llvm/include/llvm/CodeGen/MachineFunction.h
@@ -376,6 +376,7 @@ class LLVM_ABI MachineFunction {
bool HasEHCatchret = false;
bool HasEHScopes = false;
bool HasEHFunclets = false;
+ bool HasFakeUses = false;
bool IsOutlined = false;
/// BBID to assign to the next basic block of this function.
@@ -1200,6 +1201,9 @@ class LLVM_ABI MachineFunction {
bool hasEHFunclets() const { return HasEHFunclets; }
void setHasEHFunclets(bool V) { HasEHFunclets = V; }
+ bool hasFakeUses() const { return HasFakeUses; }
+ void setHasFakeUses(bool V) { HasFakeUses = V; }
+
bool isOutlined() const { return IsOutlined; }
void setIsOutlined(bool V) { IsOutlined = V; }
diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index 8e860a1f740295..c2132f8e742196 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -2199,6 +2199,7 @@ bool IRTranslator::translateKnownIntrinsic(const CallInst &CI, Intrinsic::ID ID,
for (auto VReg : getOrCreateVRegs(*Arg))
VRegs.push_back(VReg);
MIRBuilder.buildInstr(TargetOpcode::FAKE_USE, {}, VRegs);
+ MF->setHasFakeUses(true);
return true;
}
case Intrinsic::dbg_declare: {
diff --git a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
index be07fbf478b1d8..c9ec07d302e094 100644
--- a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
@@ -525,6 +525,7 @@ MIRParserImpl::initializeMachineFunction(const yaml::MachineFunction &YamlMF,
MF.setHasEHCatchret(YamlMF.HasEHCatchret);
MF.setHasEHScopes(YamlMF.HasEHScopes);
MF.setHasEHFunclets(YamlMF.HasEHFunclets);
+ MF.setHasFakeUses(YamlMF.HasFakeUses);
MF.setIsOutlined(YamlMF.IsOutlined);
if (YamlMF.Legalized)
diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
index cf6122bce22364..d52c1d831267f6 100644
--- a/llvm/lib/CodeGen/MIRPrinter.cpp
+++ b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -207,6 +207,7 @@ void MIRPrinter::print(const MachineFunction &MF) {
YamlMF.HasEHCatchret = MF.hasEHCatchret();
YamlMF.HasEHScopes = MF.hasEHScopes();
YamlMF.HasEHFunclets = MF.hasEHFunclets();
+ YamlMF.HasFakeUses = MF.hasFakeUses();
YamlMF.IsOutlined = MF.isOutlined();
YamlMF.UseDebugInstrRef = MF.useDebugInstrRef();
diff --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 9b2862de22b690..729fdb473c8449 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -477,7 +477,7 @@ bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
}
bool PostMachineScheduler::runOnMachineFunction(MachineFunction &mf) {
- if (skipFunction(mf.getFunction()))
+ if (mf.hasFakeUses() || skipFunction(mf.getFunction()))
return false;
if (EnablePostRAMachineSched.getNumOccurrences()) {
diff --git a/llvm/lib/CodeGen/PostRASchedulerList.cpp b/llvm/lib/CodeGen/PostRASchedulerList.cpp
index 2f7cfdd275b4fd..66f2f86e7f8321 100644
--- a/llvm/lib/CodeGen/PostRASchedulerList.cpp
+++ b/llvm/lib/CodeGen/PostRASchedulerList.cpp
@@ -275,7 +275,7 @@ bool PostRAScheduler::enablePostRAScheduler(
}
bool PostRAScheduler::runOnMachineFunction(MachineFunction &Fn) {
- if (skipFunction(Fn.getFunction()))
+ if (Fn.hasFakeUses() || skipFunction(Fn.getFunction()))
return false;
TII = Fn.getSubtarget().getInstrInfo();
diff --git a/llvm/lib/CodeGen/RemoveLoadsIntoFakeUses.cpp b/llvm/lib/CodeGen/RemoveLoadsIntoFakeUses.cpp
index 232181a199b8c2..ef7a58670c3ac5 100644
--- a/llvm/lib/CodeGen/RemoveLoadsIntoFakeUses.cpp
+++ b/llvm/lib/CodeGen/RemoveLoadsIntoFakeUses.cpp
@@ -74,10 +74,8 @@ INITIALIZE_PASS_END(RemoveLoadsIntoFakeUses, DEBUG_TYPE,
"Remove Loads Into Fake Uses", false, false)
bool RemoveLoadsIntoFakeUses::runOnMachineFunction(MachineFunction &MF) {
- // Only `optdebug` functions should contain FAKE_USEs, so don't try to run
- // this for other functions.
- if (!MF.getFunction().hasFnAttribute(Attribute::OptimizeForDebugging) ||
- skipFunction(MF.getFunction()))
+ // Only run this for functions that have fake uses.
+ if (!MF.hasFakeUses() || skipFunction(MF.getFunction()))
return false;
bool AnyChanges = false;
diff --git a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 8405ba9ac326cf..c075e30011b64c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -31,6 +31,7 @@
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
@@ -200,12 +201,16 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
}
}
}
- // Look for calls to the @llvm.va_start intrinsic. We can omit some
- // prologue boilerplate for variadic functions that don't examine their
- // arguments.
if (const auto *II = dyn_cast<IntrinsicInst>(&I)) {
+ // Look for calls to the @llvm.va_start intrinsic. We can omit some
+ // prologue boilerplate for variadic functions that don't examine
+ // their arguments.
if (II->getIntrinsicID() == Intrinsic::vastart)
MF->getFrameInfo().setHasVAStart(true);
+ // Look for llvm.fake.uses, so that we can prevent certain
+ // optimizations if they are present.
+ else if (II->getIntrinsicID() == Intrinsic::fake_use)
+ MF->setHasFakeUses(true);
}
// If we have a musttail call in a variadic function, we need to ensure
diff --git a/llvm/test/CodeGen/X86/fake-use-postra-scheduler.mir b/llvm/test/CodeGen/X86/fake-use-postra-scheduler.mir
new file mode 100644
index 00000000000000..1f0f5cfa22400e
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fake-use-postra-scheduler.mir
@@ -0,0 +1,55 @@
+# Prevent the post-RA machine scheduler from running on functions marked as having fake uses.
+# RUN: llc --post-RA-scheduler -run-pass post-RA-sched -mtriple=x86_64-unknown-linux --print-before=post-RA-sched --debug-only=post-RA-sched %s -o - 2>&1 >/dev/null | FileCheck %s --check-prefix=CHECK-POSTRA
+# RUN: llc --enable-post-misched=true -run-pass postmisched -mtriple=x86_64-unknown-linux --debug-only=machine-scheduler %s -o - 2>&1 >/dev/null | FileCheck %s --check-prefix=CHECK-POSTMACHINE
+# REQUIRES: asserts
+#
+# We make sure that functions that have hasFakeUses=true are not processed by
+# either of the post-regalloc scheduling passes.
+#
+# CHECK-POSTRA: Machine code for function withFakeUse
+# CHECK-POSTRA-NOT: PostRAScheduler
+# CHECK-POSTRA: Machine code for function withoutFakeUse
+# CHECK-POSTRA: PostRAScheduler
+#
+# CHECK-POSTMACHINE-NOT: Before post-MI-sched
+# CHECK-POSTMACHINE: Before post-MI-sched
+# CHECK-POSTMACHINE: Machine code for function withoutFakeUse
+#
+--- |
+ ; ModuleID = 'test.ll'
+ source_filename = "test.ll"
+ target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+
+ define void @withFakeUse() {
+ entry:
+ ret void
+ }
+
+ define void @withoutFakeUse() {
+ entry:
+ ret void
+ }
+
+...
+---
+name: withFakeUse
+alignment: 16
+hasFakeUses: true
+tracksRegLiveness: true
+registers:
+body: |
+ bb.0.entry:
+ RET 0
+
+...
+---
+name: withoutFakeUse
+alignment: 16
+hasFakeUses: false
+tracksRegLiveness: true
+registers:
+body: |
+ bb.0.entry:
+ RET 0
+
+...
diff --git a/llvm/test/tools/llvm-reduce/mir/preserve-func-info.mir b/llvm/test/tools/llvm-reduce/mir/preserve-func-info.mir
index f735dfd5cbbf01..d55a11a07f1731 100644
--- a/llvm/test/tools/llvm-reduce/mir/preserve-func-info.mir
+++ b/llvm/test/tools/llvm-reduce/mir/preserve-func-info.mir
@@ -22,6 +22,7 @@
# RESULT-NEXT: hasEHCatchret: true
# RESULT-NEXT: hasEHScopes: true
# RESULT-NEXT: hasEHFunclets: true
+# RESULT-NEXT: hasFakeUses: true
# RESULT-NEXT: failsVerification: true
# RESULT-NEXT: tracksDebugUserValues: true
@@ -54,6 +55,7 @@ callsUnwindInit: true
hasEHCatchret: true
hasEHScopes: true
hasEHFunclets: true
+hasFakeUses: true
body: |
bb.0:
diff --git a/llvm/tools/llvm-reduce/ReducerWorkItem.cpp b/llvm/tools/llvm-reduce/ReducerWorkItem.cpp
index 5409b6dc7459d3..5f6a22cb3a9741 100644
--- a/llvm/tools/llvm-reduce/ReducerWorkItem.cpp
+++ b/llvm/tools/llvm-reduce/ReducerWorkItem.cpp
@@ -403,6 +403,7 @@ static std::unique_ptr<MachineFunction> cloneMF(MachineFunction *SrcMF,
DstMF->setHasEHCatchret(SrcMF->hasEHCatchret());
DstMF->setHasEHScopes(SrcMF->hasEHScopes());
DstMF->setHasEHFunclets(SrcMF->hasEHFunclets());
+ DstMF->setHasFakeUses(SrcMF->hasFakeUses());
DstMF->setIsOutlined(SrcMF->isOutlined());
if (!SrcMF->getLandingPads().empty() ||
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