[llvm] r281484 - [ARM] Promote small global constants to constant pools
Evgenii Stepanov via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 14 12:57:17 PDT 2016
Hi,
this is adding text relocations to ARM binaries, which makes Android
loader unhappy:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/25362/steps/run%20asan%20lit%20tests%20%5Barm%2Fbullhead-userdebug%2FMTC20F%5D/logs/stdio
WARNING: linker: /system/bin/llvm-symbolizer has text relocations.
This is wasting memory and prevents security hardening. Please fix.
It that intentional?
On Wed, Sep 14, 2016 at 7:47 AM, James Molloy via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: jamesm
> Date: Wed Sep 14 09:47:27 2016
> New Revision: 281484
>
> URL: http://llvm.org/viewvc/llvm-project?rev=281484&view=rev
> Log:
> [ARM] Promote small global constants to constant pools
>
> If a constant is unamed_addr and is only used within one function, we can save
> on the code size and runtime cost of an indirection by changing the global's storage
> to inside the constant pool. For example, instead of:
>
> ldr r0, .CPI0
> bl printf
> bx lr
> .CPI0: &format_string
> format_string: .asciz "hello, world!\n"
>
> We can emit:
>
> adr r0, .CPI0
> bl printf
> bx lr
> .CPI0: .asciz "hello, world!\n"
>
> This can cause significant code size savings when many small strings are used in one
> function (4 bytes per string).
>
> Added:
> llvm/trunk/test/CodeGen/ARM/constantpool-promote.ll
> Modified:
> llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp
> llvm/trunk/lib/Target/ARM/ARMAsmPrinter.h
> llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
> llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h
>
> Modified: llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp?rev=281484&r1=281483&r2=281484&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp Wed Sep 14 09:47:27 2016
> @@ -97,6 +97,13 @@ void ARMAsmPrinter::EmitXXStructor(const
> OutStreamer->EmitValue(E, Size);
> }
>
> +void ARMAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
> + if (PromotedGlobals.count(GV))
> + // The global was promoted into a constant pool. It should not be emitted.
> + return;
> + AsmPrinter::EmitGlobalVariable(GV);
> +}
> +
> /// runOnMachineFunction - This uses the EmitInstruction()
> /// method to print assembly for each instruction.
> ///
> @@ -109,6 +116,12 @@ bool ARMAsmPrinter::runOnMachineFunction
> const Function* F = MF.getFunction();
> const TargetMachine& TM = MF.getTarget();
>
> + // Collect all globals that had their storage promoted to a constant pool.
> + // Functions are emitted before variables, so this accumulates promoted
> + // globals from all functions in PromotedGlobals.
> + for (auto *GV : AFI->getGlobalsPromotedToConstantPool())
> + PromotedGlobals.insert(GV);
> +
> // Calculate this function's optimization goal.
> unsigned OptimizationGoal;
> if (F->hasFnAttribute(Attribute::OptimizeNone))
>
> Modified: llvm/trunk/lib/Target/ARM/ARMAsmPrinter.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMAsmPrinter.h?rev=281484&r1=281483&r2=281484&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMAsmPrinter.h (original)
> +++ llvm/trunk/lib/Target/ARM/ARMAsmPrinter.h Wed Sep 14 09:47:27 2016
> @@ -56,6 +56,12 @@ class LLVM_LIBRARY_VISIBILITY ARMAsmPrin
> /// -1 if uninitialized, 0 if conflicting goals
> int OptimizationGoals;
>
> + /// List of globals that have had their storage promoted to a constant
> + /// pool. This lives between calls to runOnMachineFunction and collects
> + /// data from every MachineFunction. It is used during doFinalization
> + /// when all non-function globals are emitted.
> + SmallPtrSet<const GlobalVariable*,2> PromotedGlobals;
> +
> public:
> explicit ARMAsmPrinter(TargetMachine &TM,
> std::unique_ptr<MCStreamer> Streamer);
> @@ -90,7 +96,8 @@ public:
> void EmitStartOfAsmFile(Module &M) override;
> void EmitEndOfAsmFile(Module &M) override;
> void EmitXXStructor(const DataLayout &DL, const Constant *CV) override;
> -
> + void EmitGlobalVariable(const GlobalVariable *GV) override;
> +
> // lowerOperand - Convert a MachineOperand into the equivalent MCOperand.
> bool lowerOperand(const MachineOperand &MO, MCOperand &MCOp);
>
>
> Modified: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp?rev=281484&r1=281483&r2=281484&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp Wed Sep 14 09:47:27 2016
> @@ -59,12 +59,24 @@ using namespace llvm;
> STATISTIC(NumTailCalls, "Number of tail calls");
> STATISTIC(NumMovwMovt, "Number of GAs materialized with movw + movt");
> STATISTIC(NumLoopByVals, "Number of loops generated for byval arguments");
> +STATISTIC(NumConstpoolPromoted,
> + "Number of constants with their storage promoted into constant pools");
>
> static cl::opt<bool>
> ARMInterworking("arm-interworking", cl::Hidden,
> cl::desc("Enable / disable ARM interworking (for debugging only)"),
> cl::init(true));
>
> +static cl::opt<bool> EnableConstpoolPromotion(
> + "arm-promote-constant", cl::Hidden,
> + cl::desc("Enable / disable promotion of unnamed_addr constants into "
> + "constant pools"),
> + cl::init(true));
> +static cl::opt<unsigned> ConstpoolPromotionMaxSize(
> + "arm-promote-constant-max-size", cl::Hidden,
> + cl::desc("Maximum size of constant to promote into a constant pool"),
> + cl::init(64));
> +
> namespace {
> class ARMCCState : public CCState {
> public:
> @@ -2963,6 +2975,100 @@ ARMTargetLowering::LowerGlobalTLSAddress
> llvm_unreachable("bogus TLS model");
> }
>
> +/// Return true if all users of V are within function F, looking through
> +/// ConstantExprs.
> +static bool allUsersAreInFunction(const Value *V, const Function *F) {
> + SmallVector<const User*,4> Worklist;
> + for (auto *U : V->users())
> + Worklist.push_back(U);
> + while (!Worklist.empty()) {
> + auto *U = Worklist.pop_back_val();
> + if (isa<ConstantExpr>(U)) {
> + for (auto *UU : U->users())
> + Worklist.push_back(UU);
> + continue;
> + }
> +
> + auto *I = dyn_cast<Instruction>(U);
> + if (!I || I->getParent()->getParent() != F)
> + return false;
> + }
> + return true;
> +}
> +
> +/// Return true if all users of V are within some (any) function, looking through
> +/// ConstantExprs. In other words, are there any global constant users?
> +static bool allUsersAreInFunctions(const Value *V) {
> + SmallVector<const User*,4> Worklist;
> + for (auto *U : V->users())
> + Worklist.push_back(U);
> + while (!Worklist.empty()) {
> + auto *U = Worklist.pop_back_val();
> + if (isa<ConstantExpr>(U)) {
> + for (auto *UU : U->users())
> + Worklist.push_back(UU);
> + continue;
> + }
> +
> + if (!isa<Instruction>(U))
> + return false;
> + }
> + return true;
> +}
> +
> +static SDValue promoteToConstantPool(const GlobalValue *GV, SelectionDAG &DAG,
> + EVT PtrVT, SDLoc dl) {
> + // If we're creating a pool entry for a constant global with unnamed address,
> + // and the global is small enough, we can emit it inline into the constant pool
> + // to save ourselves an indirection.
> + //
> + // This is a win if the constant is only used in one function (so it doesn't
> + // need to be duplicated) or duplicating the constant wouldn't increase code
> + // size (implying the constant is no larger than 4 bytes).
> + const Function *F = DAG.getMachineFunction().getFunction();
> + auto *GVar = dyn_cast<GlobalVariable>(GV);
> + if (EnableConstpoolPromotion && GVar && GVar->hasInitializer() &&
> + GVar->isConstant() && GVar->hasGlobalUnnamedAddr() && GVar->hasLocalLinkage()) {
> + // The constant islands pass can only really deal with alignment requests
> + // <= 4 bytes and cannot pad constants itself. Therefore we cannot promote
> + // any type wanting greater alignment requirements than 4 bytes. We also
> + // can only promote constants that are multiples of 4 bytes in size or
> + // are paddable to a multiple of 4. Currently we only try and pad constants
> + // that are strings for simplicity.
> + auto *Init = GVar->getInitializer();
> + auto *CDAInit = dyn_cast<ConstantDataArray>(Init);
> + unsigned Size = DAG.getDataLayout().getTypeAllocSize(Init->getType());
> + unsigned Align = DAG.getDataLayout().getABITypeAlignment(Init->getType());
> + unsigned RequiredPadding = 4 - (Size % 4);
> + bool PaddingPossible =
> + RequiredPadding == 4 || (CDAInit && CDAInit->isString());
> +
> + if (PaddingPossible && Align <= 4 && Size <= ConstpoolPromotionMaxSize &&
> + (allUsersAreInFunction(GVar, F) ||
> + (Size <= 4 && allUsersAreInFunctions(GVar)))) {
> + if (RequiredPadding != 4) {
> + StringRef S = CDAInit->getAsString();
> +
> + SmallVector<uint8_t,16> V(S.size());
> + std::copy(S.bytes_begin(), S.bytes_end(), V.begin());
> + while (RequiredPadding--)
> + V.push_back(0);
> + Init = ConstantDataArray::get(*DAG.getContext(), V);
> + }
> +
> + SDValue CPAddr =
> + DAG.getTargetConstantPool(Init, PtrVT, Align);
> +
> + MachineFunction &MF = DAG.getMachineFunction();
> + ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
> + AFI->markGlobalAsPromotedToConstantPool(GVar);
> + ++NumConstpoolPromoted;
> + return DAG.getNode(ARMISD::Wrapper, dl, MVT::i32, CPAddr);
> + }
> + }
> + return SDValue();
> +}
> +
> SDValue ARMTargetLowering::LowerGlobalAddressELF(SDValue Op,
> SelectionDAG &DAG) const {
> EVT PtrVT = getPointerTy(DAG.getDataLayout());
> @@ -2974,6 +3080,11 @@ SDValue ARMTargetLowering::LowerGlobalAd
> bool IsRO =
> (isa<GlobalVariable>(GV) && cast<GlobalVariable>(GV)->isConstant()) ||
> isa<Function>(GV);
> +
> + if (TM.shouldAssumeDSOLocal(*GV->getParent(), GV))
> + if (SDValue V = promoteToConstantPool(GV, DAG, PtrVT, dl))
> + return V;
> +
> if (isPositionIndependent()) {
> bool UseGOT_PREL = !TM.shouldAssumeDSOLocal(*GV->getParent(), GV);
>
>
> Modified: llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h?rev=281484&r1=281483&r2=281484&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h (original)
> +++ llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h Wed Sep 14 09:47:27 2016
> @@ -121,6 +121,9 @@ class ARMFunctionInfo : public MachineFu
> /// copies.
> bool IsSplitCSR;
>
> + /// Globals that have had their storage promoted into the constant pool.
> + SmallVector<const GlobalVariable*,2> PromotedGlobals;
> +
> public:
> ARMFunctionInfo() :
> isThumb(false),
> @@ -226,6 +229,16 @@ public:
> }
> return It;
> }
> +
> + /// Indicate to the backend that \c GV has had its storage changed to inside
> + /// a constant pool. This means it no longer needs to be emitted as a
> + /// global variable.
> + void markGlobalAsPromotedToConstantPool(const GlobalVariable *GV) {
> + PromotedGlobals.push_back(GV);
> + }
> + ArrayRef<const GlobalVariable*> getGlobalsPromotedToConstantPool() {
> + return PromotedGlobals;
> + }
> };
> } // End llvm namespace
>
>
> Added: llvm/trunk/test/CodeGen/ARM/constantpool-promote.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/constantpool-promote.ll?rev=281484&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/constantpool-promote.ll (added)
> +++ llvm/trunk/test/CodeGen/ARM/constantpool-promote.ll Wed Sep 14 09:47:27 2016
> @@ -0,0 +1,109 @@
> +; RUN: llc -relocation-model=static < %s | FileCheck %s
> +; RUN: llc -relocation-model=pic < %s | FileCheck %s
> +; RUN: llc -relocation-model=ropi < %s | FileCheck %s
> +; RUN: llc -relocation-model=rwpi < %s | FileCheck %s
> +
> +target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-n32-S64"
> +target triple = "armv7--linux-gnueabihf"
> +
> + at .str = private unnamed_addr constant [2 x i8] c"s\00", align 1
> + at .str1 = private unnamed_addr constant [69 x i8] c"this string is far too long to fit in a literal pool by far and away\00", align 1
> + at .str2 = private unnamed_addr constant [27 x i8] c"this string is just right!\00", align 1
> + at .str3 = private unnamed_addr constant [26 x i8] c"this string is used twice\00", align 1
> + at .str4 = private unnamed_addr constant [29 x i8] c"same string in two functions\00", align 1
> + at .arr1 = private unnamed_addr constant [2 x i16] [i16 3, i16 4], align 2
> + at .arr2 = private unnamed_addr constant [2 x i16] [i16 7, i16 8], align 2
> + at .ptr = private unnamed_addr constant [2 x i16*] [i16* getelementptr inbounds ([2 x i16], [2 x i16]* @.arr2, i32 0, i32 0), i16* null], align 2
> +
> +; CHECK-LABEL: @test1
> +; CHECK: adr r0, [[x:.*]]
> +; CHECK: [[x]]:
> +; CHECK: .asciz "s\000\000"
> +define void @test1() #0 {
> + tail call void @a(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +declare void @a(i8*) #1
> +
> +; CHECK-LABEL: @test2
> +; CHECK-NOT: .asci
> +; CHECK: .fnend
> +define void @test2() #0 {
> + tail call void @a(i8* getelementptr inbounds ([69 x i8], [69 x i8]* @.str1, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +; CHECK-LABEL: @test3
> +; CHECK: adr r0, [[x:.*]]
> +; CHECK: [[x]]:
> +; CHECK: .asciz "this string is just right!\000"
> +define void @test3() #0 {
> + tail call void @a(i8* getelementptr inbounds ([27 x i8], [27 x i8]* @.str2, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +
> +; CHECK-LABEL: @test4
> +; CHECK: adr r{{.*}}, [[x:.*]]
> +; CHECK: [[x]]:
> +; CHECK: .asciz "this string is used twice\000\000"
> +define void @test4() #0 {
> + tail call void @a(i8* getelementptr inbounds ([26 x i8], [26 x i8]* @.str3, i32 0, i32 0)) #2
> + tail call void @a(i8* getelementptr inbounds ([26 x i8], [26 x i8]* @.str3, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +; CHECK-LABEL: @test5a
> +; CHECK-NOT: adr
> +define void @test5a() #0 {
> + tail call void @a(i8* getelementptr inbounds ([29 x i8], [29 x i8]* @.str4, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +define void @test5b() #0 {
> + tail call void @b(i8* getelementptr inbounds ([29 x i8], [29 x i8]* @.str4, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +; CHECK-LABEL: @test6a
> +; CHECK: adr r0, [[x:.*]]
> +; CHECK: [[x]]:
> +; CHECK: .short 3
> +; CHECK: .short 4
> +define void @test6a() #0 {
> + tail call void @c(i16* getelementptr inbounds ([2 x i16], [2 x i16]* @.arr1, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +; CHECK-LABEL: @test6b
> +; CHECK: adr r0, [[x:.*]]
> +; CHECK: [[x]]:
> +; CHECK: .short 3
> +; CHECK: .short 4
> +define void @test6b() #0 {
> + tail call void @c(i16* getelementptr inbounds ([2 x i16], [2 x i16]* @.arr1, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +; This shouldn't be promoted, as the string is used by another global.
> +; CHECK-LABEL: @test7
> +; CHECK-NOT: adr
> +define void @test7() #0 {
> + tail call void @c(i16* getelementptr inbounds ([2 x i16], [2 x i16]* @.arr2, i32 0, i32 0)) #2
> + ret void
> +}
> +
> +declare void @b(i8*) #1
> +declare void @c(i16*) #1
> +
> +attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
> +attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
> +attributes #2 = { nounwind }
> +
> +!llvm.module.flags = !{!0, !1}
> +!llvm.ident = !{!2}
> +
> +!0 = !{i32 1, !"wchar_size", i32 4}
> +!1 = !{i32 1, !"min_enum_size", i32 4}
> +!2 = !{!"Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)"}
>
>
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