return true;
}
+/// \brief Helper method for \see EvaluateSymbolAdd().
+static void AttemptToFoldSymbolOffsetDifference(const MCAsmLayout *Layout,
+ const MCSymbolRefExpr *&A,
+ const MCSymbolRefExpr *&B,
+ int64_t &Addend) {
+ const MCAssembler &Asm = Layout->getAssembler();
+
+ if (A && B &&
+ Asm.getWriter().IsSymbolRefDifferenceFullyResolved(Asm, A, B)) {
+ // Eagerly evaluate.
+ Addend += (Layout->getSymbolOffset(&Asm.getSymbolData(A->getSymbol())) -
+ Layout->getSymbolOffset(&Asm.getSymbolData(B->getSymbol())));
+
+ // Clear the symbol expr pointers to indicate we have folded these
+ // operands.
+ A = B = 0;
+ }
+}
+
+/// \brief Evaluate the result of an add between (conceptually) two MCValues.
+///
+/// This routine conceptually attempts to construct an MCValue:
+/// Result = (Result_A - Result_B + Result_Cst)
+/// from two MCValue's LHS and RHS where
+/// Result = LHS + RHS
+/// and
+/// Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
+///
+/// This routine attempts to aggresively fold the operands such that the result
+/// is representable in an MCValue, but may not always succeed.
+///
+/// \returns True on success, false if the result is not representable in an
+/// MCValue.
+
+/// NOTE: It is really important to have both the Asm and Layout arguments.
+/// They might look redundant, but this function can be used before layout
+/// is done (see the object streamer for example) and having the Asm argument
+/// lets us avoid relocations.
static bool EvaluateSymbolicAdd(const MCAssembler *Asm,
const MCAsmLayout *Layout,
const SectionAddrMap *Addrs,
const MCValue &LHS,const MCSymbolRefExpr *RHS_A,
const MCSymbolRefExpr *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))
+ // FIXME: This routine (and other evaluation parts) are *incredibly* sloppy
+ // about dealing with modifiers. This will ultimately bite us, one day.
+ const MCSymbolRefExpr *LHS_A = LHS.getSymA();
+ const MCSymbolRefExpr *LHS_B = LHS.getSymB();
+ int64_t LHS_Cst = LHS.getConstant();
+
+ // Fold the result constant immediately.
+ int64_t Result_Cst = LHS_Cst + RHS_Cst;
+
+ // If we have a layout, we can fold resolved differences.
+ if (Layout) {
+ // First, fold out any differences which are fully resolved. By
+ // reassociating terms in
+ // Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
+ // we have the four possible differences:
+ // (LHS_A - LHS_B),
+ // (LHS_A - RHS_B),
+ // (RHS_A - LHS_B),
+ // (RHS_A - RHS_B).
+ // Since we are attempting to be as aggresive as possible about folding, we
+ // attempt to evaluate each possible alternative.
+ AttemptToFoldSymbolOffsetDifference(Layout, LHS_A, LHS_B, Result_Cst);
+ AttemptToFoldSymbolOffsetDifference(Layout, LHS_A, RHS_B, Result_Cst);
+ AttemptToFoldSymbolOffsetDifference(Layout, RHS_A, LHS_B, Result_Cst);
+ AttemptToFoldSymbolOffsetDifference(Layout, RHS_A, RHS_B, Result_Cst);
+ }
+
+ // We can't represent the addition or subtraction of two symbols.
+ if ((LHS_A && RHS_A) || (LHS_B && RHS_B))
return false;
- const MCSymbolRefExpr *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
- const MCSymbolRefExpr *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 in order to encode the expression. 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)
- return false;
- }
+ // At this point, we have at most one additive symbol and one subtractive
+ // symbol -- find them.
+ const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A;
+ const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B;
+
+ // If we have a negated symbol, then we must have also have a non-negated
+ // symbol in order to encode the expression.
+ if (B && !A)
+ return false;
// Absolutize symbol differences between defined symbols when we have a
// layout object and the target requests it.
- assert(!(Layout && !Asm));
+ assert((!Layout || Asm) &&
+ "Must have an assembler object if layout is given!");
if (Asm && A && B) {
const MCSymbol &SA = A->getSymbol();
if (AD.getFragment() == BD.getFragment()) {
Res = MCValue::get(+ AD.getOffset()
- BD.getOffset()
- + LHS.getConstant()
- + RHS_Cst);
+ + Result_Cst);
return true;
}
const MCSectionData &SecB = *BD.getFragment()->getParent();
int64_t Val = + Layout->getSymbolOffset(&AD)
- Layout->getSymbolOffset(&BD)
- + LHS.getConstant()
- + RHS_Cst;
+ + Result_Cst;
if (&SecA != &SecB) {
if (!Addrs)
return false;
}
}
- Res = MCValue::get(A, B, LHS.getConstant() + RHS_Cst);
+ Res = MCValue::get(A, B, Result_Cst);
return true;
}
projects / oota-llvm.git / blobdiff