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Allow negative offsets in MipsMCInstLower::LowerOperand

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Summary:
We rely on this in our CHERI backend to address the GOT by generating a
$pc-relative addresses. For this we emit the following code sequence:

lui $1, %pcrel_hi(_CHERI_CAPABILITY_TABLE_-8)
daddiu $1, $1, %pcrel_lo(_CHERI_CAPABILITY_TABLE_-4)
cgetpccincoffset $c1, $1

However, without this change the addend is implicitly converted to
UINT32_MAX and an invalid pointer value is generated.

Reviewers: atanasyan

Reviewed By: atanasyan

Subscribers: merge_guards_bot, sdardis, hiraditya, jrtc27, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70953
This commit is contained in:
Alex Richardson 2019-12-04 10:06:24 +00:00
parent 8a152514d8
commit 1e20340b43
2 changed files with 5 additions and 7 deletions
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8
lib/Target/Mips/MipsMCInstLower.cpp
View File

@ -34,7 +34,7 @@ void MipsMCInstLower::Initialize(MCContext *C) {
MCOperand MipsMCInstLower::LowerSymbolOperand(const MachineOperand &MO,
MachineOperandType MOTy,
unsigned Offset) const {
int64_t Offset) const {
MCSymbolRefExpr::VariantKind Kind = MCSymbolRefExpr::VK_None;
MipsMCExpr::MipsExprKind TargetKind = MipsMCExpr::MEK_None;
bool IsGpOff = false;
@ -161,9 +161,7 @@ MCOperand MipsMCInstLower::LowerSymbolOperand(const MachineOperand &MO,
const MCExpr *Expr = MCSymbolRefExpr::create(Symbol, Kind, *Ctx);
if (Offset) {
// Assume offset is never negative.
assert(Offset > 0);
// Note: Offset can also be negative
Expr = MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, *Ctx),
*Ctx);
}
@ -177,7 +175,7 @@ MCOperand MipsMCInstLower::LowerSymbolOperand(const MachineOperand &MO,
}
MCOperand MipsMCInstLower::LowerOperand(const MachineOperand &MO,
unsigned offset) const {
int64_t offset) const {
MachineOperandType MOTy = MO.getType();
switch (MOTy) {

4
lib/Target/Mips/MipsMCInstLower.h
View File

@ -35,11 +35,11 @@ public:
void Initialize(MCContext *C);
void Lower(const MachineInstr *MI, MCInst &OutMI) const;
MCOperand LowerOperand(const MachineOperand& MO, unsigned offset = 0) const;
MCOperand LowerOperand(const MachineOperand &MO, int64_t offset = 0) const;
private:
MCOperand LowerSymbolOperand(const MachineOperand &MO,
MachineOperandType MOTy, unsigned Offset) const;
MachineOperandType MOTy, int64_t Offset) const;
MCOperand createSub(MachineBasicBlock *BB1, MachineBasicBlock *BB2,
MipsMCExpr::MipsExprKind Kind) const;
void lowerLongBranchLUi(const MachineInstr *MI, MCInst &OutMI) const;