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llvm-mc: Rewrite binary subtraction for relocatable expressions, we can't always

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legally negate an MCValue.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74497 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Daniel Dunbar 2009-06-30 02:08:27 +00:00
parent 15d1707096
commit 3597604e5e
1 changed files with 33 additions and 26 deletions
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59
tools/llvm-mc/AsmExpr.cpp
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@ -26,6 +26,29 @@ bool AsmExpr::EvaluateAsAbsolute(MCContext &Ctx, int64_t &Res) const {
return true;
}
static bool EvaluateSymbolicAdd(const MCValue &LHS, MCSymbol *RHS_A,
MCSymbol *RHS_B, int64_t RHS_Cst,
MCValue &Res) {
// We can't add or subtract two symbols.
if ((LHS.getSymA() && RHS_A) ||
(LHS.getSymB() && RHS_B))
return false;
MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
if (B) {
// If we have a negated symbol, then we must have also have a
// non-negated symbol, and both symbols must be in the same
// non-external section. We can do this check later to permit
// expressions which eventually fold to a representable form -- such
// as (a + (0 - b)) -- if necessary.
if (!A || !A->getSection() || A->getSection() != B->getSection())
return false;
}
Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
return true;
}
bool AsmExpr::EvaluateAsRelocatable(MCContext &Ctx, MCValue &Res) const {
switch (getKind()) {
default:
@ -92,33 +115,17 @@ bool AsmExpr::EvaluateAsRelocatable(MCContext &Ctx, MCValue &Res) const {
default:
return false;
case AsmBinaryExpr::Sub:
// Negate RHS and fall through.
RHSValue = MCValue::get(RHSValue.getSymB(), RHSValue.getSymA(),
-RHSValue.getConstant());
// Negate RHS and add.
return EvaluateSymbolicAdd(LHSValue,
RHSValue.getSymB(), RHSValue.getSymA(),
-RHSValue.getConstant(),
Res);
case AsmBinaryExpr::Add:
// (a_0 - b_0 + cst_0) + (a_1 - b_1 + cst_1)
// We can't add or subtract two symbols.
if ((LHSValue.getSymA() && RHSValue.getSymB()) ||
(LHSValue.getSymB() && RHSValue.getSymB()))
return false;
MCSymbol *A =
LHSValue.getSymA() ? LHSValue.getSymA() : RHSValue.getSymA();
MCSymbol *B =
LHSValue.getSymB() ? LHSValue.getSymB() : RHSValue.getSymB();
if (B) {
// If we have a negated symbol, then we must have also have a
// non-negated symbol, and both symbols must be in the same
// non-external section. We can do this check later to permit
// expressions which eventually fold to a representable form -- such
// as (a + (0 - b)) -- if necessary.
if (!A || !A->getSection() || A->getSection() != B->getSection())
return false;
}
Res = MCValue::get(A, B,
LHSValue.getConstant() + RHSValue.getConstant());
return true;
return EvaluateSymbolicAdd(LHSValue,
RHSValue.getSymA(), RHSValue.getSymB(),
RHSValue.getConstant(),
Res);
}
}