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committedDec 8, 2016
IR, X86: Understand !absolute_symbol metadata on global variables.
Summary: Attaching !absolute_symbol to a global variable does two things: 1) Marks it as an absolute symbol reference. 2) Specifies the value range of that symbol's address. Teach the X86 backend to allow absolute symbols to appear in place of immediates by extending the relocImm and mov64imm32 matchers. Start using relocImm in more places where it is legal. As previously proposed on llvm-dev: http://lists.llvm.org/pipermail/llvm-dev/2016-October/105800.html Differential Revision: https://reviews.llvm.org/D25878 llvm-svn: 289087
·
llvmorg-21-initllvmorg-4.0.0-rc1
1 parent aa4f445 commit 235c275

17 files changed

+289
-15
lines changed
 

‎llvm/docs/LangRef.rst

+19
Original file line numberDiff line numberDiff line change
@@ -4589,6 +4589,25 @@ Examples:
45894589
!2 = !{ i8 0, i8 2, i8 3, i8 6 }
45904590
!3 = !{ i8 -2, i8 0, i8 3, i8 6 }
45914591
4592+
'``absolute_symbol``' Metadata
4593+
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4594+
4595+
``absolute_symbol`` metadata may be attached to a global variable
4596+
declaration. It marks the declaration as a reference to an absolute symbol,
4597+
which causes the backend to use absolute relocations for the symbol even
4598+
in position independent code, and expresses the possible ranges that the
4599+
global variable's *address* (not its value) is in, in the same format as
4600+
``range`` metadata.
4601+
4602+
Example:
4603+
4604+
.. code-block:: llvm
4605+
4606+
@a = external global i8, !absolute_symbol !0 ; Absolute symbol in range [0,256)
4607+
4608+
...
4609+
!0 = !{ i64 0, i64 256 }
4610+
45924611
'``unpredictable``' Metadata
45934612
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
45944613

‎llvm/include/llvm/IR/GlobalValue.h

+8
Original file line numberDiff line numberDiff line change
@@ -33,6 +33,7 @@
3333
namespace llvm {
3434

3535
class Comdat;
36+
class ConstantRange;
3637
class Error;
3738
class GlobalObject;
3839
class Module;
@@ -511,6 +512,13 @@ class GlobalValue : public Constant {
511512
}
512513
GlobalObject *getBaseObject();
513514

515+
/// Returns whether this is a reference to an absolute symbol.
516+
bool isAbsoluteSymbolRef() const;
517+
518+
/// If this is an absolute symbol reference, returns the range of the symbol,
519+
/// otherwise returns None.
520+
Optional<ConstantRange> getAbsoluteSymbolRange() const;
521+
514522
/// This method unlinks 'this' from the containing module, but does not delete
515523
/// it.
516524
virtual void removeFromParent() = 0;

‎llvm/include/llvm/IR/LLVMContext.h

+1
Original file line numberDiff line numberDiff line change
@@ -77,6 +77,7 @@ class LLVMContext {
7777
MD_loop = 18, // "llvm.loop"
7878
MD_type = 19, // "type"
7979
MD_section_prefix = 20, // "section_prefix"
80+
MD_absolute_symbol = 21, // "absolute_symbol"
8081
};
8182

8283
/// Known operand bundle tag IDs, which always have the same value. All

‎llvm/lib/Analysis/ValueTracking.cpp

+4-4
Original file line numberDiff line numberDiff line change
@@ -3345,11 +3345,11 @@ bool llvm::isKnownNonNull(const Value *V) {
33453345
if (const Argument *A = dyn_cast<Argument>(V))
33463346
return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr();
33473347

3348-
// A global variable in address space 0 is non null unless extern weak.
3349-
// Other address spaces may have null as a valid address for a global,
3350-
// so we can't assume anything.
3348+
// A global variable in address space 0 is non null unless extern weak
3349+
// or an absolute symbol reference. Other address spaces may have null as a
3350+
// valid address for a global, so we can't assume anything.
33513351
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
3352-
return !GV->hasExternalWeakLinkage() &&
3352+
return !GV->isAbsoluteSymbolRef() && !GV->hasExternalWeakLinkage() &&
33533353
GV->getType()->getAddressSpace() == 0;
33543354

33553355
// A Load tagged with nonnull metadata is never null.

‎llvm/lib/IR/Globals.cpp

+21
Original file line numberDiff line numberDiff line change
@@ -15,6 +15,7 @@
1515
#include "llvm/ADT/SmallPtrSet.h"
1616
#include "llvm/ADT/Triple.h"
1717
#include "llvm/IR/Constants.h"
18+
#include "llvm/IR/ConstantRange.h"
1819
#include "llvm/IR/DerivedTypes.h"
1920
#include "llvm/IR/GlobalAlias.h"
2021
#include "llvm/IR/GlobalValue.h"
@@ -222,6 +223,26 @@ GlobalObject *GlobalValue::getBaseObject() {
222223
return nullptr;
223224
}
224225

226+
bool GlobalValue::isAbsoluteSymbolRef() const {
227+
auto *GO = dyn_cast<GlobalObject>(this);
228+
if (!GO)
229+
return false;
230+
231+
return GO->getMetadata(LLVMContext::MD_absolute_symbol);
232+
}
233+
234+
Optional<ConstantRange> GlobalValue::getAbsoluteSymbolRange() const {
235+
auto *GO = dyn_cast<GlobalObject>(this);
236+
if (!GO)
237+
return None;
238+
239+
MDNode *MD = GO->getMetadata(LLVMContext::MD_absolute_symbol);
240+
if (!MD)
241+
return None;
242+
243+
return getConstantRangeFromMetadata(*MD);
244+
}
245+
225246
//===----------------------------------------------------------------------===//
226247
// GlobalVariable Implementation
227248
//===----------------------------------------------------------------------===//

‎llvm/lib/IR/LLVMContext.cpp

+1
Original file line numberDiff line numberDiff line change
@@ -57,6 +57,7 @@ LLVMContext::LLVMContext() : pImpl(new LLVMContextImpl(*this)) {
5757
{MD_loop, "llvm.loop"},
5858
{MD_type, "type"},
5959
{MD_section_prefix, "section_prefix"},
60+
{MD_absolute_symbol, "absolute_symbol"},
6061
};
6162

6263
for (auto &MDKind : MDKinds) {

‎llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

+40-2
Original file line numberDiff line numberDiff line change
@@ -24,6 +24,7 @@
2424
#include "llvm/CodeGen/MachineInstrBuilder.h"
2525
#include "llvm/CodeGen/MachineRegisterInfo.h"
2626
#include "llvm/CodeGen/SelectionDAGISel.h"
27+
#include "llvm/IR/ConstantRange.h"
2728
#include "llvm/IR/Function.h"
2829
#include "llvm/IR/Instructions.h"
2930
#include "llvm/IR/Intrinsics.h"
@@ -1571,7 +1572,15 @@ bool X86DAGToDAGISel::selectMOV64Imm32(SDValue N, SDValue &Imm) {
15711572
return false;
15721573

15731574
Imm = N;
1574-
return TM.getCodeModel() == CodeModel::Small;
1575+
if (N->getOpcode() != ISD::TargetGlobalAddress)
1576+
return TM.getCodeModel() == CodeModel::Small;
1577+
1578+
Optional<ConstantRange> CR =
1579+
cast<GlobalAddressSDNode>(N)->getGlobal()->getAbsoluteSymbolRange();
1580+
if (!CR)
1581+
return TM.getCodeModel() == CodeModel::Small;
1582+
1583+
return CR->getUnsignedMax().ult(1ull << 32);
15751584
}
15761585

15771586
bool X86DAGToDAGISel::selectLEA64_32Addr(SDValue N, SDValue &Base,
@@ -1710,10 +1719,39 @@ bool X86DAGToDAGISel::selectRelocImm(SDValue N, SDValue &Op) {
17101719
return true;
17111720
}
17121721

1722+
// Keep track of the original value type and whether this value was
1723+
// truncated. If we see a truncation from pointer type to VT that truncates
1724+
// bits that are known to be zero, we can use a narrow reference.
1725+
EVT VT = N.getValueType();
1726+
bool WasTruncated = false;
1727+
if (N.getOpcode() == ISD::TRUNCATE) {
1728+
WasTruncated = true;
1729+
N = N.getOperand(0);
1730+
}
1731+
17131732
if (N.getOpcode() != X86ISD::Wrapper)
17141733
return false;
17151734

1716-
Op = N.getOperand(0);
1735+
// We can only use non-GlobalValues as immediates if they were not truncated,
1736+
// as we do not have any range information. If we have a GlobalValue and the
1737+
// address was not truncated, we can select it as an operand directly.
1738+
unsigned Opc = N.getOperand(0)->getOpcode();
1739+
if (Opc != ISD::TargetGlobalAddress || !WasTruncated) {
1740+
Op = N.getOperand(0);
1741+
// We can only select the operand directly if we didn't have to look past a
1742+
// truncate.
1743+
return !WasTruncated;
1744+
}
1745+
1746+
// Check that the global's range fits into VT.
1747+
auto *GA = cast<GlobalAddressSDNode>(N.getOperand(0));
1748+
Optional<ConstantRange> CR = GA->getGlobal()->getAbsoluteSymbolRange();
1749+
if (!CR || CR->getUnsignedMax().uge(1ull << VT.getSizeInBits()))
1750+
return false;
1751+
1752+
// Okay, we can use a narrow reference.
1753+
Op = CurDAG->getTargetGlobalAddress(GA->getGlobal(), SDLoc(N), VT,
1754+
GA->getOffset(), GA->getTargetFlags());
17171755
return true;
17181756
}
17191757

‎llvm/lib/Target/X86/X86ISelLowering.cpp

+6-2
Original file line numberDiff line numberDiff line change
@@ -13676,7 +13676,11 @@ static SDValue LowerINSERT_SUBVECTOR(SDValue Op, const X86Subtarget &Subtarget,
1367613676
}
1367713677

1367813678
// Returns the appropriate wrapper opcode for a global reference.
13679-
unsigned X86TargetLowering::getGlobalWrapperKind() const {
13679+
unsigned X86TargetLowering::getGlobalWrapperKind(const GlobalValue *GV) const {
13680+
// References to absolute symbols are never PC-relative.
13681+
if (GV && GV->isAbsoluteSymbolRef())
13682+
return X86ISD::Wrapper;
13683+
1368013684
CodeModel::Model M = getTargetMachine().getCodeModel();
1368113685
if (Subtarget.isPICStyleRIPRel() &&
1368213686
(M == CodeModel::Small || M == CodeModel::Kernel))
@@ -13805,7 +13809,7 @@ SDValue X86TargetLowering::LowerGlobalAddress(const GlobalValue *GV,
1380513809
Result = DAG.getTargetGlobalAddress(GV, dl, PtrVT, 0, OpFlags);
1380613810
}
1380713811

13808-
Result = DAG.getNode(getGlobalWrapperKind(), dl, PtrVT, Result);
13812+
Result = DAG.getNode(getGlobalWrapperKind(GV), dl, PtrVT, Result);
1380913813

1381013814
// With PIC, the address is actually $g + Offset.
1381113815
if (isGlobalRelativeToPICBase(OpFlags)) {

‎llvm/lib/Target/X86/X86ISelLowering.h

+1-1
Original file line numberDiff line numberDiff line change
@@ -1115,7 +1115,7 @@ namespace llvm {
11151115
SDValue InsertBitToMaskVector(SDValue Op, SelectionDAG &DAG) const;
11161116
SDValue LowerINSERT_VECTOR_ELT(SDValue Op, SelectionDAG &DAG) const;
11171117

1118-
unsigned getGlobalWrapperKind() const;
1118+
unsigned getGlobalWrapperKind(const GlobalValue *GV = nullptr) const;
11191119
SDValue LowerConstantPool(SDValue Op, SelectionDAG &DAG) const;
11201120
SDValue LowerBlockAddress(SDValue Op, SelectionDAG &DAG) const;
11211121
SDValue LowerGlobalAddress(const GlobalValue *GV, const SDLoc &dl,

‎llvm/lib/Target/X86/X86InstrInfo.td

+2-2
Original file line numberDiff line numberDiff line change
@@ -948,10 +948,10 @@ def i64immSExt32 : ImmLeaf<i64, [{ return isInt<32>(Imm); }]>;
948948
// Eventually, it would be nice to allow ConstantHoisting to merge constants
949949
// globally for potentially added savings.
950950
//
951-
def imm8_su : PatLeaf<(i8 imm), [{
951+
def imm8_su : PatLeaf<(i8 relocImm), [{
952952
return !shouldAvoidImmediateInstFormsForSize(N);
953953
}]>;
954-
def imm16_su : PatLeaf<(i16 imm), [{
954+
def imm16_su : PatLeaf<(i16 relocImm), [{
955955
return !shouldAvoidImmediateInstFormsForSize(N);
956956
}]>;
957957
def imm32_su : PatLeaf<(i32 relocImm), [{

‎llvm/lib/Target/X86/X86InstrShiftRotate.td

+5-4
Original file line numberDiff line numberDiff line change
@@ -591,19 +591,20 @@ def ROR64rCL : RI<0xD3, MRM1r, (outs GR64:$dst), (ins GR64:$src1),
591591

592592
def ROR8ri : Ii8<0xC0, MRM1r, (outs GR8 :$dst), (ins GR8 :$src1, u8imm:$src2),
593593
"ror{b}\t{$src2, $dst|$dst, $src2}",
594-
[(set GR8:$dst, (rotr GR8:$src1, (i8 imm:$src2)))], IIC_SR>;
594+
[(set GR8:$dst, (rotr GR8:$src1, (i8 relocImm:$src2)))],
595+
IIC_SR>;
595596
def ROR16ri : Ii8<0xC1, MRM1r, (outs GR16:$dst), (ins GR16:$src1, u8imm:$src2),
596597
"ror{w}\t{$src2, $dst|$dst, $src2}",
597-
[(set GR16:$dst, (rotr GR16:$src1, (i8 imm:$src2)))],
598+
[(set GR16:$dst, (rotr GR16:$src1, (i8 relocImm:$src2)))],
598599
IIC_SR>, OpSize16;
599600
def ROR32ri : Ii8<0xC1, MRM1r, (outs GR32:$dst), (ins GR32:$src1, u8imm:$src2),
600601
"ror{l}\t{$src2, $dst|$dst, $src2}",
601-
[(set GR32:$dst, (rotr GR32:$src1, (i8 imm:$src2)))],
602+
[(set GR32:$dst, (rotr GR32:$src1, (i8 relocImm:$src2)))],
602603
IIC_SR>, OpSize32;
603604
def ROR64ri : RIi8<0xC1, MRM1r, (outs GR64:$dst),
604605
(ins GR64:$src1, u8imm:$src2),
605606
"ror{q}\t{$src2, $dst|$dst, $src2}",
606-
[(set GR64:$dst, (rotr GR64:$src1, (i8 imm:$src2)))],
607+
[(set GR64:$dst, (rotr GR64:$src1, (i8 relocImm:$src2)))],
607608
IIC_SR>;
608609

609610
// Rotate by 1

‎llvm/lib/Target/X86/X86Subtarget.cpp

+4
Original file line numberDiff line numberDiff line change
@@ -92,6 +92,10 @@ unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
9292
if (TM.getCodeModel() == CodeModel::Large)
9393
return X86II::MO_NO_FLAG;
9494

95+
// Absolute symbols can be referenced directly.
96+
if (GV && GV->isAbsoluteSymbolRef())
97+
return X86II::MO_NO_FLAG;
98+
9599
if (TM.shouldAssumeDSOLocal(M, GV))
96100
return classifyLocalReference(GV);
97101

‎llvm/test/CodeGen/X86/absolute-bit-mask.ll

+61
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,61 @@
1+
; RUN: llc < %s | FileCheck %s
2+
; RUN: llc -relocation-model=pic < %s | FileCheck %s
3+
4+
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
5+
target triple = "x86_64-unknown-linux-gnu"
6+
7+
@bit_mask8 = external hidden global i8, !absolute_symbol !0
8+
@bit_mask32 = external hidden global i8, !absolute_symbol !1
9+
@bit_mask64 = external hidden global i8, !absolute_symbol !2
10+
11+
declare void @f()
12+
13+
define void @foo8(i8* %ptr) {
14+
%load = load i8, i8* %ptr
15+
; CHECK: testb $bit_mask8, (%rdi)
16+
%and = and i8 %load, ptrtoint (i8* @bit_mask8 to i8)
17+
%icmp = icmp eq i8 %and, 0
18+
br i1 %icmp, label %t, label %f
19+
20+
t:
21+
call void @f()
22+
ret void
23+
24+
f:
25+
ret void
26+
}
27+
28+
define void @foo32(i32* %ptr) {
29+
%load = load i32, i32* %ptr
30+
; CHECK: testl $bit_mask32, (%rdi)
31+
%and = and i32 %load, ptrtoint (i8* @bit_mask32 to i32)
32+
%icmp = icmp eq i32 %and, 0
33+
br i1 %icmp, label %t, label %f
34+
35+
t:
36+
call void @f()
37+
ret void
38+
39+
f:
40+
ret void
41+
}
42+
43+
define void @foo64(i64* %ptr) {
44+
%load = load i64, i64* %ptr
45+
; CHECK: movabsq $bit_mask64, %rax
46+
; CHECK: testq (%rdi), %rax
47+
%and = and i64 %load, ptrtoint (i8* @bit_mask64 to i64)
48+
%icmp = icmp eq i64 %and, 0
49+
br i1 %icmp, label %t, label %f
50+
51+
t:
52+
call void @f()
53+
ret void
54+
55+
f:
56+
ret void
57+
}
58+
59+
!0 = !{i64 0, i64 256}
60+
!1 = !{i64 0, i64 4294967296}
61+
!2 = !{i64 -1, i64 -1}

‎llvm/test/CodeGen/X86/absolute-bt.ll

+51
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,51 @@
1+
; RUN: llc < %s | FileCheck %s
2+
; RUN: llc -relocation-model=pic < %s | FileCheck %s
3+
4+
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
5+
target triple = "x86_64-unknown-linux-gnu"
6+
7+
@bit_mask8 = external hidden global i8, !absolute_symbol !0
8+
@bit_mask32 = external hidden global i8, !absolute_symbol !1
9+
@bit_mask64 = external hidden global i8, !absolute_symbol !2
10+
11+
declare void @f()
12+
13+
define void @foo32(i32* %ptr) {
14+
%load = load i32, i32* %ptr
15+
%and = and i32 %load, 31
16+
%shl = shl i32 1, %and
17+
%and2 = and i32 %shl, ptrtoint (i8* @bit_mask32 to i32)
18+
; CHECK: movl $bit_mask32, %eax
19+
; CHECK: btl %ecx, %eax
20+
%icmp = icmp eq i32 %and2, 0
21+
br i1 %icmp, label %t, label %f
22+
23+
t:
24+
call void @f()
25+
ret void
26+
27+
f:
28+
ret void
29+
}
30+
31+
define void @foo64(i64* %ptr) {
32+
%load = load i64, i64* %ptr
33+
%and = and i64 %load, 63
34+
%shl = shl i64 1, %and
35+
%and2 = and i64 %shl, ptrtoint (i8* @bit_mask64 to i64)
36+
; CHECK: movabsq $bit_mask64, %rax
37+
; CHECK: btq %rcx, %rax
38+
%icmp = icmp eq i64 %and2, 0
39+
br i1 %icmp, label %t, label %f
40+
41+
t:
42+
call void @f()
43+
ret void
44+
45+
f:
46+
ret void
47+
}
48+
49+
!0 = !{i64 0, i64 256}
50+
!1 = !{i64 0, i64 4294967296}
51+
!2 = !{i64 -1, i64 -1}

‎llvm/test/CodeGen/X86/absolute-constant.ll

+28
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,28 @@
1+
; RUN: llc < %s | FileCheck %s
2+
; RUN: llc -relocation-model=pic < %s | FileCheck %s
3+
4+
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
5+
target triple = "x86_64-unknown-linux-gnu"
6+
7+
@foo = external global i8, align 1, !absolute_symbol !0
8+
9+
define void @bar(i8* %x) {
10+
entry:
11+
%0 = load i8, i8* %x, align 1
12+
%conv = sext i8 %0 to i32
13+
; CHECK: testb $foo, (%rdi)
14+
%and = and i32 %conv, sext (i8 ptrtoint (i8* @foo to i8) to i32)
15+
%tobool = icmp eq i32 %and, 0
16+
br i1 %tobool, label %if.end, label %if.then
17+
18+
if.then: ; preds = %entry
19+
tail call void (...) @xf()
20+
br label %if.end
21+
22+
if.end: ; preds = %entry, %if.then
23+
ret void
24+
}
25+
26+
declare void @xf(...)
27+
28+
!0 = !{i32 0, i32 256}

‎llvm/test/CodeGen/X86/absolute-rotate.ll

+27
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,27 @@
1+
; RUN: llc < %s | FileCheck %s
2+
; RUN: llc -relocation-model=pic < %s | FileCheck %s
3+
4+
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
5+
target triple = "x86_64-unknown-linux-gnu"
6+
7+
@align = external hidden global i8, !absolute_symbol !0
8+
9+
declare void @f()
10+
11+
define void @foo(i64 %val) {
12+
%shr = lshr i64 %val, zext (i8 ptrtoint (i8* @align to i8) to i64)
13+
%shl = shl i64 %val, zext (i8 sub (i8 64, i8 ptrtoint (i8* @align to i8)) to i64)
14+
; CHECK: rorq $align, %rdi
15+
%ror = or i64 %shr, %shl
16+
%cmp = icmp ult i64 %ror, 109
17+
br i1 %cmp, label %t, label %f
18+
19+
t:
20+
call void @f()
21+
ret void
22+
23+
f:
24+
ret void
25+
}
26+
27+
!0 = !{i64 0, i64 256}

‎llvm/test/Transforms/FunctionAttrs/nonnull-global.ll

+10
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,10 @@
1+
; RUN: opt -S -functionattrs %s | FileCheck %s
2+
3+
@a = external global i8, !absolute_symbol !0
4+
5+
; CHECK-NOT: define nonnull
6+
define i8* @foo() {
7+
ret i8* @a
8+
}
9+
10+
!0 = !{i64 0, i64 256}

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