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RISCV: clean up target expression handling

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The target specific expression handling was slightly regressed by
bbea64250f65480d787e1c5ff45c4de3ec2dcda8.  This restores the proper
sub-expression evaluation to allow for constant folding within the
expression.  We explicitly discard the layout and assembler when
evaluating the expression to avoid any symbolic computation and instead
using the `evaluateAsRelocatable` to canonicalise and constant fold
only.

We can also simplify the expression handling - none of the target
variants support symbolic difference.  This simplifies the logic for
that and adds additional tests to ensure that we do not accidentally
regress here in the future.

Reviewed By: maskray

Differential Revision: https://reviews.llvm.org/D104473
This commit is contained in:
Saleem Abdulrasool 2021-06-17 17:09:22 +00:00 committed by Saleem Abdulrasool
parent 921bd72ae7
commit 0c385efcae
2 changed files with 38 additions and 26 deletions
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35
lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp
View File

@ -92,33 +92,16 @@ const MCFixup *RISCVMCExpr::getPCRelHiFixup(const MCFragment **DFOut) const {
bool RISCVMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
const MCAsmLayout *Layout,
const MCFixup *Fixup) const {
bool IsSymbolicDifference = false;
if (const auto *MBE = dyn_cast<MCBinaryExpr>(getSubExpr())) {
if (isa<MCBinaryExpr>(MBE->getLHS()) && isa<MCConstantExpr>(MBE->getRHS()))
MBE = cast<MCBinaryExpr>(MBE->getLHS());
IsSymbolicDifference = isa<MCSymbolRefExpr>(MBE->getLHS()) &&
isa<MCSymbolRefExpr>(MBE->getRHS());
}
// Explicitly drop the layout and assembler to prevent any symbolic folding in
// the expression handling. This is required to preserve symbolic difference
// expressions to emit the paired relocations.
if (!getSubExpr()->evaluateAsRelocatable(Res, nullptr, nullptr))
return false;
// Some custom fixup types are not valid with symbol difference expressions
if (IsSymbolicDifference) {
switch (getKind()) {
default:
break;
case VK_RISCV_LO:
case VK_RISCV_HI:
case VK_RISCV_PCREL_LO:
case VK_RISCV_PCREL_HI:
case VK_RISCV_GOT_HI:
case VK_RISCV_TPREL_LO:
case VK_RISCV_TPREL_HI:
case VK_RISCV_TPREL_ADD:
case VK_RISCV_TLS_GOT_HI:
case VK_RISCV_TLS_GD_HI:
return false;
}
}
return getSubExpr()->evaluateAsRelocatable(Res, Layout, Fixup);
Res =
MCValue::get(Res.getSymA(), Res.getSymB(), Res.getConstant(), getKind());
// Custom fixup types are not valid with symbol difference expressions.
return Res.getSymB() ? getKind() == VK_RISCV_None : true;
}
void RISCVMCExpr::visitUsedExpr(MCStreamer &Streamer) const {

29
test/MC/RISCV/expressions.s Normal file
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@ -0,0 +1,29 @@
# RUN: not llvm-mc -triple riscv32 -filetype obj %s -o /dev/null 2>&1 | FileCheck %s
.Ltmp1:
.quad tls
lui a0, %hi(tls+0-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
lw a0, %lo(tls+0-.Ltmp1)(t0)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
lui a0, %tprel_hi(tls+0-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
add a0, a0, tp, %tprel_add(tls+0-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
addi a0, a0, %tprel_lo(tls+0-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
auipc a0, %tls_ie_pcrel_hi(tls+0-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
auipc a0, %tls_gd_pcrel_hi(tls+0-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
auipc a0, %pcrel_hi(tls-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
auipc a0, %got_pcrel_hi(tls-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
addi a0, a0, %pcrel_lo(tls-.Ltmp1)
# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
# tail tls+32
# tail tls-tls
# _ :[[#@LINE-1]]:2: error: expected relocatable expression