Change the model for FP Stack return to use fp operands on the
RET instruction instead of using FpSET_ST0_32. This also generalizes
the code to handling returning of multiple FP results.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48209 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86FloatingPoint.cpp b/lib/Target/X86/X86FloatingPoint.cpp
index fa1b0eb..6ee79c1 100644
--- a/lib/Target/X86/X86FloatingPoint.cpp
+++ b/lib/Target/X86/X86FloatingPoint.cpp
@@ -75,26 +75,31 @@
cerr << "\n";
}
private:
+ /// isStackEmpty - Return true if the FP stack is empty.
+ bool isStackEmpty() const {
+ return StackTop == 0;
+ }
+
// getSlot - Return the stack slot number a particular register number is
- // in...
+ // in.
unsigned getSlot(unsigned RegNo) const {
assert(RegNo < 8 && "Regno out of range!");
return RegMap[RegNo];
}
- // getStackEntry - Return the X86::FP<n> register in register ST(i)
+ // getStackEntry - Return the X86::FP<n> register in register ST(i).
unsigned getStackEntry(unsigned STi) const {
assert(STi < StackTop && "Access past stack top!");
return Stack[StackTop-1-STi];
}
// getSTReg - Return the X86::ST(i) register which contains the specified
- // FP<RegNo> register
+ // FP<RegNo> register.
unsigned getSTReg(unsigned RegNo) const {
return StackTop - 1 - getSlot(RegNo) + llvm::X86::ST0;
}
- // pushReg - Push the specified FP<n> register onto the stack
+ // pushReg - Push the specified FP<n> register onto the stack.
void pushReg(unsigned Reg) {
assert(Reg < 8 && "Register number out of range!");
assert(StackTop < 8 && "Stack overflow!");
@@ -103,22 +108,22 @@
}
bool isAtTop(unsigned RegNo) const { return getSlot(RegNo) == StackTop-1; }
- void moveToTop(unsigned RegNo, MachineBasicBlock::iterator &I) {
- if (!isAtTop(RegNo)) {
- unsigned STReg = getSTReg(RegNo);
- unsigned RegOnTop = getStackEntry(0);
+ void moveToTop(unsigned RegNo, MachineBasicBlock::iterator I) {
+ if (isAtTop(RegNo)) return;
+
+ unsigned STReg = getSTReg(RegNo);
+ unsigned RegOnTop = getStackEntry(0);
- // Swap the slots the regs are in
- std::swap(RegMap[RegNo], RegMap[RegOnTop]);
+ // Swap the slots the regs are in.
+ std::swap(RegMap[RegNo], RegMap[RegOnTop]);
- // Swap stack slot contents
- assert(RegMap[RegOnTop] < StackTop);
- std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);
+ // Swap stack slot contents.
+ assert(RegMap[RegOnTop] < StackTop);
+ std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);
- // Emit an fxch to update the runtime processors version of the state
- BuildMI(*MBB, I, TII->get(X86::XCH_F)).addReg(STReg);
- NumFXCH++;
- }
+ // Emit an fxch to update the runtime processors version of the state.
+ BuildMI(*MBB, I, TII->get(X86::XCH_F)).addReg(STReg);
+ NumFXCH++;
}
void duplicateToTop(unsigned RegNo, unsigned AsReg, MachineInstr *I) {
@@ -268,7 +273,7 @@
Changed = true;
}
- assert(StackTop == 0 && "Stack not empty at end of basic block?");
+ assert(isStackEmpty() && "Stack not empty at end of basic block?");
return Changed;
}
@@ -960,6 +965,83 @@
duplicateToTop(SrcReg, DestReg, I);
}
break;
+ case X86::RET:
+ case X86::RETI:
+ // If RET has an FP register use operand, pass the first one in ST(0) and
+ // the second one in ST(1).
+ if (isStackEmpty()) return; // Quick check to see if any are possible.
+
+ // Find the register operands.
+ unsigned FirstFPRegOp = ~0U, SecondFPRegOp = ~0U;
+
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand &Op = MI->getOperand(i);
+ if (!Op.isReg() || Op.getReg() < X86::FP0 || Op.getReg() > X86::FP6)
+ continue;
+ assert(Op.isUse() && Op.isKill() &&
+ "Ret only defs operands, and values aren't live beyond it");
+
+ if (FirstFPRegOp == ~0U)
+ FirstFPRegOp = getFPReg(Op);
+ else {
+ assert(SecondFPRegOp == ~0U && "More than two fp operands!");
+ SecondFPRegOp = getFPReg(Op);
+ }
+
+ // Remove the operand so that later passes don't see it.
+ MI->RemoveOperand(i);
+ --i, --e;
+ }
+
+ // There are only four possibilities here:
+ // 1) we are returning a single FP value. In this case, it has to be in
+ // ST(0) already, so just declare success by removing the value from the
+ // FP Stack.
+ if (SecondFPRegOp == ~0U) {
+ // Assert that the top of stack contains the right FP register.
+ assert(StackTop == 1 && FirstFPRegOp == getStackEntry(0) &&
+ "Top of stack not the right register for RET!");
+
+ // Ok, everything is good, mark the value as not being on the stack
+ // anymore so that our assertion about the stack being empty at end of
+ // block doesn't fire.
+ StackTop = 0;
+ return;
+ }
+
+ assert(0 && "TODO: This code should work, but has never been tested."
+ "Test it when we have multiple FP return values working");
+
+ // Otherwise, we are returning two values:
+ // 2) If returning the same value for both, we only have one thing in the FP
+ // stack. Consider: RET FP1, FP1
+ if (StackTop == 1) {
+ assert(FirstFPRegOp == SecondFPRegOp && FirstFPRegOp == getStackEntry(0)&&
+ "Stack misconfiguration for RET!");
+
+ // Duplicate the TOS so that we return it twice. Just pick some other FPx
+ // register to hold it.
+ unsigned NewReg = (FirstFPRegOp+1)%7;
+ duplicateToTop(FirstFPRegOp, NewReg, MI);
+ FirstFPRegOp = NewReg;
+ }
+
+ /// Okay we know we have two different FPx operands now:
+ assert(StackTop == 2 && "Must have two values live!");
+
+ /// 3) If SecondFPRegOp is currently in ST(0) and FirstFPRegOp is currently
+ /// in ST(1). In this case, emit an fxch.
+ if (getStackEntry(0) == SecondFPRegOp) {
+ assert(getStackEntry(1) == FirstFPRegOp && "Unknown regs live");
+ moveToTop(FirstFPRegOp, MI);
+ }
+
+ /// 4) Finally, FirstFPRegOp must be in ST(0) and SecondFPRegOp must be in
+ /// ST(1). Just remove both from our understanding of the stack and return.
+ assert(getStackEntry(0) == FirstFPRegOp && "Unknown regs live");
+ assert(getStackEntry(0) == SecondFPRegOp && "Unknown regs live");
+ StackTop = 0;
+ return;
}
}