[llvm] r355522 - [IR][ARM] Add function pointer alignment to datalayout
Michael Platings via llvm-commits
llvm-commits at lists.llvm.org
Wed Mar 6 09:24:11 PST 2019
Author: michaelplatings
Date: Wed Mar 6 09:24:11 2019
New Revision: 355522
URL: http://llvm.org/viewvc/llvm-project?rev=355522&view=rev
Log:
[IR][ARM] Add function pointer alignment to datalayout
Use this feature to fix a bug on ARM where 4 byte alignment is
incorrectly assumed.
Differential Revision: https://reviews.llvm.org/D57335
Added:
llvm/trunk/unittests/IR/DataLayoutTest.cpp
Modified:
llvm/trunk/docs/LangRef.rst
llvm/trunk/include/llvm/IR/DataLayout.h
llvm/trunk/lib/IR/ConstantFold.cpp
llvm/trunk/lib/IR/DataLayout.cpp
llvm/trunk/lib/IR/Value.cpp
llvm/trunk/lib/Target/ARM/ARMTargetMachine.cpp
llvm/trunk/unittests/IR/CMakeLists.txt
llvm/trunk/unittests/IR/ConstantsTest.cpp
llvm/trunk/unittests/IR/FunctionTest.cpp
Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Wed Mar 6 09:24:11 2019
@@ -2004,6 +2004,14 @@ as follows:
targets.
``a:<abi>:<pref>``
This specifies the alignment for an object of aggregate type.
+``F<type><abi>``
+ This specifies the alignment for function pointers.
+ The options for ``<type>`` are:
+
+ * ``i``: The alignment of function pointers is independent of the alignment
+ of functions, and is a multiple of ``<abi>``.
+ * ``n``: The alignment of function pointers is a multiple of the explicit
+ alignment specified on the function, and is a multiple of ``<abi>``.
``m:<mangling>``
If present, specifies that llvm names are mangled in the output. Symbols
prefixed with the mangling escape character ``\01`` are passed through
Modified: llvm/trunk/include/llvm/IR/DataLayout.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/DataLayout.h?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/DataLayout.h (original)
+++ llvm/trunk/include/llvm/IR/DataLayout.h Wed Mar 6 09:24:11 2019
@@ -108,6 +108,13 @@ struct PointerAlignElem {
/// generating LLVM IR is required to generate the right target data for the
/// target being codegen'd to.
class DataLayout {
+public:
+ enum class FunctionPtrAlignType {
+ /// The function pointer alignment is independent of the function alignment.
+ Independent,
+ /// The function pointer alignment is a multiple of the function alignment.
+ MultipleOfFunctionAlign,
+ };
private:
/// Defaults to false.
bool BigEndian;
@@ -116,6 +123,9 @@ private:
unsigned StackNaturalAlign;
unsigned ProgramAddrSpace;
+ unsigned FunctionPtrAlign;
+ FunctionPtrAlignType TheFunctionPtrAlignType;
+
enum ManglingModeT {
MM_None,
MM_ELF,
@@ -199,6 +209,8 @@ public:
BigEndian = DL.isBigEndian();
AllocaAddrSpace = DL.AllocaAddrSpace;
StackNaturalAlign = DL.StackNaturalAlign;
+ FunctionPtrAlign = DL.FunctionPtrAlign;
+ TheFunctionPtrAlignType = DL.TheFunctionPtrAlignType;
ProgramAddrSpace = DL.ProgramAddrSpace;
ManglingMode = DL.ManglingMode;
LegalIntWidths = DL.LegalIntWidths;
@@ -256,6 +268,17 @@ public:
unsigned getStackAlignment() const { return StackNaturalAlign; }
unsigned getAllocaAddrSpace() const { return AllocaAddrSpace; }
+ /// Returns the alignment of function pointers, which may or may not be
+ /// related to the alignment of functions.
+ /// \see getFunctionPtrAlignType
+ unsigned getFunctionPtrAlign() const { return FunctionPtrAlign; }
+
+ /// Return the type of function pointer alignment.
+ /// \see getFunctionPtrAlign
+ FunctionPtrAlignType getFunctionPtrAlignType() const {
+ return TheFunctionPtrAlignType;
+ }
+
unsigned getProgramAddressSpace() const { return ProgramAddrSpace; }
bool hasMicrosoftFastStdCallMangling() const {
Modified: llvm/trunk/lib/IR/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/ConstantFold.cpp?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp (original)
+++ llvm/trunk/lib/IR/ConstantFold.cpp Wed Mar 6 09:24:11 2019
@@ -26,6 +26,7 @@
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/ErrorHandling.h"
@@ -1076,10 +1077,29 @@ Constant *llvm::ConstantFoldBinaryInstru
isa<GlobalValue>(CE1->getOperand(0))) {
GlobalValue *GV = cast<GlobalValue>(CE1->getOperand(0));
- // Functions are at least 4-byte aligned.
- unsigned GVAlign = GV->getAlignment();
- if (isa<Function>(GV))
- GVAlign = std::max(GVAlign, 4U);
+ unsigned GVAlign;
+
+ if (Module *TheModule = GV->getParent()) {
+ GVAlign = GV->getPointerAlignment(TheModule->getDataLayout());
+
+ // If the function alignment is not specified then assume that it
+ // is 4.
+ // This is dangerous; on x86, the alignment of the pointer
+ // corresponds to the alignment of the function, but might be less
+ // than 4 if it isn't explicitly specified.
+ // However, a fix for this behaviour was reverted because it
+ // increased code size (see https://reviews.llvm.org/D55115)
+ // FIXME: This code should be deleted once existing targets have
+ // appropriate defaults
+ if (GVAlign == 0U && isa<Function>(GV))
+ GVAlign = 4U;
+ } else if (isa<Function>(GV)) {
+ // Without a datalayout we have to assume the worst case: that the
+ // function pointer isn't aligned at all.
+ GVAlign = 0U;
+ } else {
+ GVAlign = GV->getAlignment();
+ }
if (GVAlign > 1) {
unsigned DstWidth = CI2->getType()->getBitWidth();
Modified: llvm/trunk/lib/IR/DataLayout.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/DataLayout.cpp?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/lib/IR/DataLayout.cpp (original)
+++ llvm/trunk/lib/IR/DataLayout.cpp Wed Mar 6 09:24:11 2019
@@ -184,6 +184,8 @@ void DataLayout::reset(StringRef Desc) {
AllocaAddrSpace = 0;
StackNaturalAlign = 0;
ProgramAddrSpace = 0;
+ FunctionPtrAlign = 0;
+ TheFunctionPtrAlignType = FunctionPtrAlignType::Independent;
ManglingMode = MM_None;
NonIntegralAddressSpaces.clear();
@@ -379,6 +381,22 @@ void DataLayout::parseSpecifier(StringRe
StackNaturalAlign = inBytes(getInt(Tok));
break;
}
+ case 'F': {
+ switch (Tok.front()) {
+ case 'i':
+ TheFunctionPtrAlignType = FunctionPtrAlignType::Independent;
+ break;
+ case 'n':
+ TheFunctionPtrAlignType = FunctionPtrAlignType::MultipleOfFunctionAlign;
+ break;
+ default:
+ report_fatal_error("Unknown function pointer alignment type in "
+ "datalayout string");
+ }
+ Tok = Tok.substr(1);
+ FunctionPtrAlign = inBytes(getInt(Tok));
+ break;
+ }
case 'P': { // Function address space.
ProgramAddrSpace = getAddrSpace(Tok);
break;
@@ -432,6 +450,8 @@ bool DataLayout::operator==(const DataLa
AllocaAddrSpace == Other.AllocaAddrSpace &&
StackNaturalAlign == Other.StackNaturalAlign &&
ProgramAddrSpace == Other.ProgramAddrSpace &&
+ FunctionPtrAlign == Other.FunctionPtrAlign &&
+ TheFunctionPtrAlignType == Other.TheFunctionPtrAlignType &&
ManglingMode == Other.ManglingMode &&
LegalIntWidths == Other.LegalIntWidths &&
Alignments == Other.Alignments && Pointers == Other.Pointers;
Modified: llvm/trunk/lib/IR/Value.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Value.cpp?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Value.cpp (original)
+++ llvm/trunk/lib/IR/Value.cpp Wed Mar 6 09:24:11 2019
@@ -648,10 +648,16 @@ unsigned Value::getPointerAlignment(cons
unsigned Align = 0;
if (auto *GO = dyn_cast<GlobalObject>(this)) {
- // Don't make any assumptions about function pointer alignment. Some
- // targets use the LSBs to store additional information.
- if (isa<Function>(GO))
- return 0;
+ if (isa<Function>(GO)) {
+ switch (DL.getFunctionPtrAlignType()) {
+ case DataLayout::FunctionPtrAlignType::Independent:
+ return DL.getFunctionPtrAlign();
+ case DataLayout::FunctionPtrAlignType::MultipleOfFunctionAlign:
+ return std::max(DL.getFunctionPtrAlign(), GO->getAlignment());
+ default:
+ llvm_unreachable("unknown function pointer align type");
+ }
+ }
Align = GO->getAlignment();
if (Align == 0) {
if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
Modified: llvm/trunk/lib/Target/ARM/ARMTargetMachine.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMTargetMachine.cpp?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMTargetMachine.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMTargetMachine.cpp Wed Mar 6 09:24:11 2019
@@ -141,6 +141,10 @@ static std::string computeDataLayout(con
// Pointers are 32 bits and aligned to 32 bits.
Ret += "-p:32:32";
+ // Function pointers are aligned to 8 bits (because the LSB stores the
+ // ARM/Thumb state).
+ Ret += "-Fi8";
+
// ABIs other than APCS have 64 bit integers with natural alignment.
if (ABI != ARMBaseTargetMachine::ARM_ABI_APCS)
Ret += "-i64:64";
Modified: llvm/trunk/unittests/IR/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/CMakeLists.txt?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/unittests/IR/CMakeLists.txt (original)
+++ llvm/trunk/unittests/IR/CMakeLists.txt Wed Mar 6 09:24:11 2019
@@ -13,6 +13,7 @@ add_llvm_unittest(IRTests
CFGBuilder.cpp
ConstantRangeTest.cpp
ConstantsTest.cpp
+ DataLayoutTest.cpp
DebugInfoTest.cpp
DebugTypeODRUniquingTest.cpp
DominatorTreeTest.cpp
Modified: llvm/trunk/unittests/IR/ConstantsTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/ConstantsTest.cpp?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/unittests/IR/ConstantsTest.cpp (original)
+++ llvm/trunk/unittests/IR/ConstantsTest.cpp Wed Mar 6 09:24:11 2019
@@ -475,5 +475,105 @@ TEST(ConstantsTest, BitcastToGEP) {
ASSERT_EQ(cast<ConstantExpr>(C)->getOpcode(), Instruction::BitCast);
}
+bool foldFuncPtrAndConstToNull(LLVMContext &Context, Module *TheModule,
+ uint64_t AndValue, unsigned FunctionAlign = 0) {
+ Type *VoidType(Type::getVoidTy(Context));
+ FunctionType *FuncType(FunctionType::get(VoidType, false));
+ Function *Func(Function::Create(
+ FuncType, GlobalValue::ExternalLinkage, "", TheModule));
+
+ if (FunctionAlign) Func->setAlignment(FunctionAlign);
+
+ IntegerType *ConstantIntType(Type::getInt32Ty(Context));
+ ConstantInt *TheConstant(ConstantInt::get(ConstantIntType, AndValue));
+
+ Constant *TheConstantExpr(
+ ConstantExpr::getPtrToInt(Func, ConstantIntType));
+
+ return ConstantExpr::get(Instruction::And, TheConstantExpr,
+ TheConstant)->isNullValue();
+}
+
+TEST(ConstantsTest, FoldFunctionPtrAlignUnknownAnd2) {
+ LLVMContext Context;
+ Module TheModule("TestModule", Context);
+ // When the DataLayout doesn't specify a function pointer alignment we
+ // assume in this case that it is 4 byte aligned. This is a bug but we can't
+ // fix it directly because it causes a code size regression on X86.
+ // FIXME: This test should be changed once existing targets have
+ // appropriate defaults. See associated FIXME in ConstantFoldBinaryInstruction
+ ASSERT_TRUE(foldFuncPtrAndConstToNull(Context, &TheModule, 2));
+}
+
+TEST(ConstantsTest, DontFoldFunctionPtrAlignUnknownAnd4) {
+ LLVMContext Context;
+ Module TheModule("TestModule", Context);
+ ASSERT_FALSE(foldFuncPtrAndConstToNull(Context, &TheModule, 4));
+}
+
+TEST(ConstantsTest, FoldFunctionPtrAlign4) {
+ LLVMContext Context;
+ Module TheModule("TestModule", Context);
+ const char* AlignmentStrings[] = { "Fi32", "Fn32" };
+
+ for (unsigned AndValue = 1; AndValue <= 2; ++AndValue) {
+ for (const char *AlignmentString : AlignmentStrings) {
+ TheModule.setDataLayout(AlignmentString);
+ ASSERT_TRUE(foldFuncPtrAndConstToNull(Context, &TheModule, AndValue));
+ }
+ }
+}
+
+TEST(ConstantsTest, DontFoldFunctionPtrAlign1) {
+ LLVMContext Context;
+ Module TheModule("TestModule", Context);
+ const char* AlignmentStrings[] = { "Fi8", "Fn8" };
+
+ for (const char* AlignmentString : AlignmentStrings) {
+ TheModule.setDataLayout(AlignmentString);
+ ASSERT_FALSE(foldFuncPtrAndConstToNull(Context, &TheModule, 2));
+ }
+}
+
+TEST(ConstantsTest, FoldFunctionAlign4PtrAlignMultiple) {
+ LLVMContext Context;
+ Module TheModule("TestModule", Context);
+ TheModule.setDataLayout("Fn8");
+ ASSERT_TRUE(foldFuncPtrAndConstToNull(Context, &TheModule, 2, 4));
+}
+
+TEST(ConstantsTest, DontFoldFunctionAlign4PtrAlignIndependent) {
+ LLVMContext Context;
+ Module TheModule("TestModule", Context);
+ TheModule.setDataLayout("Fi8");
+ ASSERT_FALSE(foldFuncPtrAndConstToNull(Context, &TheModule, 2, 4));
+}
+
+TEST(ConstantsTest, DontFoldFunctionPtrIfNoModule) {
+ LLVMContext Context;
+ // Even though the function is explicitly 4 byte aligned, in the absence of a
+ // DataLayout we can't assume that the function pointer is aligned.
+ ASSERT_FALSE(foldFuncPtrAndConstToNull(Context, nullptr, 2, 4));
+}
+
+TEST(ConstantsTest, FoldGlobalVariablePtr) {
+ LLVMContext Context;
+
+
+ IntegerType *IntType(Type::getInt32Ty(Context));
+
+ GlobalVariable Global(IntType, true, GlobalValue::ExternalLinkage);
+
+ Global.setAlignment(4);
+
+ ConstantInt *TheConstant(ConstantInt::get(IntType, 2));
+
+ Constant *TheConstantExpr(
+ ConstantExpr::getPtrToInt(&Global, IntType));
+
+ ASSERT_TRUE(ConstantExpr::get( \
+ Instruction::And, TheConstantExpr, TheConstant)->isNullValue());
+}
+
} // end anonymous namespace
} // end namespace llvm
Added: llvm/trunk/unittests/IR/DataLayoutTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/DataLayoutTest.cpp?rev=355522&view=auto
==============================================================================
--- llvm/trunk/unittests/IR/DataLayoutTest.cpp (added)
+++ llvm/trunk/unittests/IR/DataLayoutTest.cpp Wed Mar 6 09:24:11 2019
@@ -0,0 +1,47 @@
+//===- ConstantRangeTest.cpp - ConstantRange tests ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/DataLayout.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(DataLayoutTest, FunctionPtrAlign) {
+ EXPECT_EQ(0U, DataLayout("").getFunctionPtrAlign());
+ EXPECT_EQ(1U, DataLayout("Fi8").getFunctionPtrAlign());
+ EXPECT_EQ(2U, DataLayout("Fi16").getFunctionPtrAlign());
+ EXPECT_EQ(4U, DataLayout("Fi32").getFunctionPtrAlign());
+ EXPECT_EQ(8U, DataLayout("Fi64").getFunctionPtrAlign());
+ EXPECT_EQ(1U, DataLayout("Fn8").getFunctionPtrAlign());
+ EXPECT_EQ(2U, DataLayout("Fn16").getFunctionPtrAlign());
+ EXPECT_EQ(4U, DataLayout("Fn32").getFunctionPtrAlign());
+ EXPECT_EQ(8U, DataLayout("Fn64").getFunctionPtrAlign());
+ EXPECT_EQ(DataLayout::FunctionPtrAlignType::Independent, \
+ DataLayout("").getFunctionPtrAlignType());
+ EXPECT_EQ(DataLayout::FunctionPtrAlignType::Independent, \
+ DataLayout("Fi8").getFunctionPtrAlignType());
+ EXPECT_EQ(DataLayout::FunctionPtrAlignType::MultipleOfFunctionAlign, \
+ DataLayout("Fn8").getFunctionPtrAlignType());
+ EXPECT_EQ(DataLayout("Fi8"), DataLayout("Fi8"));
+ EXPECT_NE(DataLayout("Fi8"), DataLayout("Fi16"));
+ EXPECT_NE(DataLayout("Fi8"), DataLayout("Fn8"));
+
+ DataLayout a(""), b("Fi8"), c("Fn8");
+ EXPECT_NE(a, b);
+ EXPECT_NE(a, c);
+ EXPECT_NE(b, c);
+
+ a = b;
+ EXPECT_EQ(a, b);
+ a = c;
+ EXPECT_EQ(a, c);
+}
+
+} // anonymous namespace
Modified: llvm/trunk/unittests/IR/FunctionTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/FunctionTest.cpp?rev=355522&r1=355521&r2=355522&view=diff
==============================================================================
--- llvm/trunk/unittests/IR/FunctionTest.cpp (original)
+++ llvm/trunk/unittests/IR/FunctionTest.cpp Wed Mar 6 09:24:11 2019
@@ -129,4 +129,29 @@ TEST(FunctionTest, setSection) {
EXPECT_TRUE(F->hasSection());
}
+TEST(FunctionTest, GetPointerAlignment) {
+ LLVMContext Context;
+ Type *VoidType(Type::getVoidTy(Context));
+ FunctionType *FuncType(FunctionType::get(VoidType, false));
+ Function *Func = Function::Create(
+ FuncType, GlobalValue::ExternalLinkage);
+ EXPECT_EQ(0U, Func->getPointerAlignment(DataLayout("")));
+ EXPECT_EQ(1U, Func->getPointerAlignment(DataLayout("Fi8")));
+ EXPECT_EQ(1U, Func->getPointerAlignment(DataLayout("Fn8")));
+ EXPECT_EQ(2U, Func->getPointerAlignment(DataLayout("Fi16")));
+ EXPECT_EQ(2U, Func->getPointerAlignment(DataLayout("Fn16")));
+ EXPECT_EQ(4U, Func->getPointerAlignment(DataLayout("Fi32")));
+ EXPECT_EQ(4U, Func->getPointerAlignment(DataLayout("Fn32")));
+
+ Func->setAlignment(4U);
+
+ EXPECT_EQ(0U, Func->getPointerAlignment(DataLayout("")));
+ EXPECT_EQ(1U, Func->getPointerAlignment(DataLayout("Fi8")));
+ EXPECT_EQ(4U, Func->getPointerAlignment(DataLayout("Fn8")));
+ EXPECT_EQ(2U, Func->getPointerAlignment(DataLayout("Fi16")));
+ EXPECT_EQ(4U, Func->getPointerAlignment(DataLayout("Fn16")));
+ EXPECT_EQ(4U, Func->getPointerAlignment(DataLayout("Fi32")));
+ EXPECT_EQ(4U, Func->getPointerAlignment(DataLayout("Fn32")));
+}
+
} // end namespace
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