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[ARM] Support constant pools in data when generating execute-only code.
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Resubmission of r305387, which was reverted at r305390. The Address
Sanitizer caught a stack-use-after-scope of a Twine variable. This
is now fixed by passing the Twine directly as a function parameter.

The ARM backend asserts against constant pool lowering when it generates
execute-only code in order to prevent the generation of constant pools in
the text section. It appears that target independent optimizations might
generate DAG nodes that represent constant pools. By lowering such nodes
as global addresses we don't violate the semantics of execute-only code
and also it is guaranteed that execute-only behaves correct with the
position-independent addressing modes that support execute-only code.

Differential Revision: https://reviews.llvm.org/D33773

llvm-svn: 305776
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@labrinea
labrinea committed Jun 20, 2017
1 parent b5c3362 commit 2b2b420
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Showing 4 changed files with 94 additions and 15 deletions.
3 changes: 3 additions & 0 deletions llvm/lib/Target/ARM/ARMAsmPrinter.cpp
View file
Expand Up @@ -1504,6 +1504,9 @@ void ARMAsmPrinter::EmitInstruction(const MachineInstr *MI) {
return;
}
case ARM::CONSTPOOL_ENTRY: {
if (Subtarget->genExecuteOnly())
llvm_unreachable("execute-only should not generate constant pools");

/// CONSTPOOL_ENTRY - This instruction represents a floating constant pool
/// in the function. The first operand is the ID# for this instruction, the
/// second is the index into the MachineConstantPool that this is, the third
Expand Down
54 changes: 39 additions & 15 deletions llvm/lib/Target/ARM/ARMISelLowering.cpp
View file
Expand Up @@ -2669,12 +2669,35 @@ static SDValue LowerWRITE_REGISTER(SDValue Op, SelectionDAG &DAG) {
// Select(N) returns N. So the raw TargetGlobalAddress nodes, etc. can only
// be used to form addressing mode. These wrapped nodes will be selected
// into MOVi.
static SDValue LowerConstantPool(SDValue Op, SelectionDAG &DAG) {
SDValue ARMTargetLowering::LowerConstantPool(SDValue Op,
SelectionDAG &DAG) const {
EVT PtrVT = Op.getValueType();
// FIXME there is no actual debug info here
SDLoc dl(Op);
ConstantPoolSDNode *CP = cast<ConstantPoolSDNode>(Op);
SDValue Res;

// When generating execute-only code Constant Pools must be promoted to the
// global data section. It's a bit ugly that we can't share them across basic
// blocks, but this way we guarantee that execute-only behaves correct with
// position-independent addressing modes.
if (Subtarget->genExecuteOnly()) {
auto AFI = DAG.getMachineFunction().getInfo<ARMFunctionInfo>();
auto T = const_cast<Type*>(CP->getType());
auto C = const_cast<Constant*>(CP->getConstVal());
auto M = const_cast<Module*>(DAG.getMachineFunction().
getFunction()->getParent());
auto GV = new GlobalVariable(
*M, T, /*isConst=*/true, GlobalVariable::InternalLinkage, C,
Twine(DAG.getDataLayout().getPrivateGlobalPrefix()) + "CP" +
Twine(DAG.getMachineFunction().getFunctionNumber()) + "_" +
Twine(AFI->createPICLabelUId())
);
SDValue GA = DAG.getTargetGlobalAddress(dyn_cast<GlobalValue>(GV),
dl, PtrVT);
return LowerGlobalAddress(GA, DAG);
}

if (CP->isMachineConstantPoolEntry())
Res = DAG.getTargetConstantPool(CP->getMachineCPVal(), PtrVT,
CP->getAlignment());
Expand Down Expand Up @@ -3118,6 +3141,19 @@ static bool isReadOnly(const GlobalValue *GV) {
isa<Function>(GV);
}

SDValue ARMTargetLowering::LowerGlobalAddress(SDValue Op,
SelectionDAG &DAG) const {
switch (Subtarget->getTargetTriple().getObjectFormat()) {
default: llvm_unreachable("unknown object format");
case Triple::COFF:
return LowerGlobalAddressWindows(Op, DAG);
case Triple::ELF:
return LowerGlobalAddressELF(Op, DAG);
case Triple::MachO:
return LowerGlobalAddressDarwin(Op, DAG);
}
}

SDValue ARMTargetLowering::LowerGlobalAddressELF(SDValue Op,
SelectionDAG &DAG) const {
EVT PtrVT = getPointerTy(DAG.getDataLayout());
Expand Down Expand Up @@ -7634,21 +7670,9 @@ SDValue ARMTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
switch (Op.getOpcode()) {
default: llvm_unreachable("Don't know how to custom lower this!");
case ISD::WRITE_REGISTER: return LowerWRITE_REGISTER(Op, DAG);
case ISD::ConstantPool:
if (Subtarget->genExecuteOnly())
llvm_unreachable("execute-only should not generate constant pools");
return LowerConstantPool(Op, DAG);
case ISD::ConstantPool: return LowerConstantPool(Op, DAG);
case ISD::BlockAddress: return LowerBlockAddress(Op, DAG);
case ISD::GlobalAddress:
switch (Subtarget->getTargetTriple().getObjectFormat()) {
default: llvm_unreachable("unknown object format");
case Triple::COFF:
return LowerGlobalAddressWindows(Op, DAG);
case Triple::ELF:
return LowerGlobalAddressELF(Op, DAG);
case Triple::MachO:
return LowerGlobalAddressDarwin(Op, DAG);
}
case ISD::GlobalAddress: return LowerGlobalAddress(Op, DAG);
case ISD::GlobalTLSAddress: return LowerGlobalTLSAddress(Op, DAG);
case ISD::SELECT: return LowerSELECT(Op, DAG);
case ISD::SELECT_CC: return LowerSELECT_CC(Op, DAG);
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2 changes: 2 additions & 0 deletions llvm/lib/Target/ARM/ARMISelLowering.h
View file
Expand Up @@ -601,6 +601,8 @@ class InstrItineraryData;
SDValue LowerINTRINSIC_WO_CHAIN(SDValue Op, SelectionDAG &DAG,
const ARMSubtarget *Subtarget) const;
SDValue LowerBlockAddress(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerConstantPool(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerGlobalAddress(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerGlobalAddressDarwin(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerGlobalAddressELF(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerGlobalAddressWindows(SDValue Op, SelectionDAG &DAG) const;
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50 changes: 50 additions & 0 deletions llvm/test/CodeGen/ARM/constantfp.ll
View file
Expand Up @@ -11,6 +11,9 @@
; RUN: llc -mtriple=thumbv7meb -arm-execute-only -mcpu=cortex-m4 %s -o - \
; RUN: | FileCheck --check-prefix=CHECK-XO-FLOAT --check-prefix=CHECK-XO-DOUBLE-BE %s

; RUN: llc -mtriple=thumbv7m -arm-execute-only -mcpu=cortex-m4 -relocation-model=ropi %s -o - \
; RUN: | FileCheck --check-prefix=CHECK-XO-ROPI %s

; RUN: llc -mtriple=thumbv8m.main -mattr=fp-armv8 %s -o - \
; RUN: | FileCheck --check-prefix=CHECK-NO-XO %s

Expand All @@ -20,6 +23,8 @@
; RUN: llc -mtriple=thumbv8m.maineb -arm-execute-only -mattr=fp-armv8 %s -o - \
; RUN: | FileCheck --check-prefix=CHECK-XO-FLOAT --check-prefix=CHECK-XO-DOUBLE-BE %s

; RUN: llc -mtriple=thumbv8m.main -arm-execute-only -mattr=fp-armv8 -relocation-model=ropi %s -o - \
; RUN: | FileCheck --check-prefix=CHECK-XO-ROPI %s

define arm_aapcs_vfpcc float @test_vmov_f32() {
; CHECK-LABEL: test_vmov_f32:
Expand Down Expand Up @@ -176,3 +181,48 @@ define arm_aapcs_vfpcc double @lower_const_f64_xo() {
; CHECK-XO-DOUBLE-BE-NOT: vldr
ret double 3.140000e-01
}

; This is a target independent optimization, performed by the
; DAG Combiner, which promotes floating point literals into
; constant pools:
;
; (a cond b) ? 1.0f : 2.0f -> load (ConstPoolAddr + ((a cond b) ? 0 : 4)
;
; We need to make sure that the constant pools are placed in
; the data section when generating execute-only code:

define arm_aapcs_vfpcc float @lower_fpconst_select(float %f) {

; CHECK-NO-XO-LABEL: lower_fpconst_select
; CHECK-NO-XO: adr [[REG:r[0-9]+]], [[LABEL:.?LCPI[0-9]+_[0-9]+]]
; CHECK-NO-XO: vldr {{s[0-9]+}}, {{[[]}}[[REG]]{{[]]}}
; CHECK-NO-XO-NOT: .rodata
; CHECK-NO-XO: [[LABEL]]:
; CHECK-NO-XO: .long 1335165689
; CHECK-NO-XO: .long 1307470632

; CHECK-XO-FLOAT-LABEL: lower_fpconst_select
; CHECK-XO-FLOAT: movw [[REG:r[0-9]+]], :lower16:[[LABEL:.?LCP[0-9]+_[0-9]+]]
; CHECK-XO-FLOAT: movt [[REG]], :upper16:[[LABEL]]
; CHECK-XO-FLOAT: vldr {{s[0-9]+}}, {{[[]}}[[REG]]{{[]]}}
; CHECK-XO-FLOAT: .rodata
; CHECK-XO-FLOAT-NOT: .text
; CHECK-XO-FLOAT: [[LABEL]]:
; CHECK-XO-FLOAT: .long 1335165689
; CHECK-XO-FLOAT: .long 1307470632

; CHECK-XO-ROPI-LABEL: lower_fpconst_select
; CHECK-XO-ROPI: movw [[REG:r[0-9]+]], :lower16:([[LABEL1:.?LCP[0-9]+_[0-9]+]]-([[LABEL2:.?LPC[0-9]+_[0-9]+]]+4))
; CHECK-XO-ROPI: movt [[REG]], :upper16:([[LABEL1]]-([[LABEL2]]+4))
; CHECK-XO-ROPI: [[LABEL2]]:
; CHECK-XO-ROPI: vldr {{s[0-9]+}}, {{[[]}}[[REG]]{{[]]}}
; CHECK-XO-ROPI: .rodata
; CHECK-XO-ROPI-NOT: .text
; CHECK-XO-ROPI: [[LABEL1]]:
; CHECK-XO-ROPI: .long 1335165689
; CHECK-XO-ROPI: .long 1307470632

%cmp = fcmp nnan oeq float %f, 0.000000e+00
%sel = select i1 %cmp, float 5.000000e+08, float 5.000000e+09
ret float %sel
}

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