================
@@ -88,47 +91,59 @@ namespace llvm {
/// In its nomenclature, the rematerializer differentiates between "original
/// registers" (registers that were present when it analyzed the function) and
/// rematerializations of these original registers. Rematerializations have an
-/// "origin" which is the index of the original regiser they were
rematerialized
-/// from (transitivity applies; a rematerialization and all of its own
-/// rematerializations have the same origin). Semantically, only original
-/// registers have rematerializations.
+/// "origin" which is the index of the original register they were
+/// rematerialized from (transitivity applies; a rematerialization and all of
+/// its own rematerializations have the same origin). Semantically, only
+/// original registers have rematerializations.
+///
+/// Dealing with sub-registers is complicated, we have to handle dead-defs,
+/// undef flags, and connected components
class Rematerializer {
public:
/// Index type for rematerializable registers.
using RegisterIdx = unsigned;
- /// A rematerializable register defined by a single machine instruction.
+ /// A rematerializable register, potentially defined by multiple
instructions.
///
/// A rematerializable register has a set of dependencies, which correspond
- /// to the unique read register operands of its defining instruction and
which
- /// can themselves be rematerializable. Operand indices corresponding to
- /// unrematerializable dependencies are managed by and queried from the
- /// rematerializer, whereas rematerializable ones are part of this struct and
- /// identified through their register index.
+ /// to the unique read register operands of its defining instruction(s) and
+ /// which can themselves be rematerializable. Operands of defining
+ /// instructions corresponding to unrematerializable dependencies are managed
+ /// by and queried from the rematerializer, whereas rematerializable ones are
+ /// part of this struct and identified through their register index.
///
/// A rematerializable register also has an arbitrary number of users in an
/// arbitrary number of regions, potentially including its own defining
/// region. When rematerializations lead to operand changes in users, a
/// register may find itself without any user left, at which point the
- /// rematerializer deletes it (setting its defining MI to nullptr).
+ /// rematerializer deletes it (emptying \ref Reg::Defs).
struct Reg {
- /// Single MI defining the rematerializable register.
- MachineInstr *DefMI;
- /// Defining region of \p DefMI.
+ /// All instructions that define the register, in program order.
+ SmallVector<MachineInstr *, 1> Defs;
+ /// Defining region of the register.
unsigned DefRegion;
/// The rematerializable register's lane bitmask.
LaneBitmask Mask;
using RegionUsers = SmallDenseSet<MachineInstr *, 4>;
- /// Uses of the register, mapped by region.
+ /// Uses of the register, mapped by region. Users that also define a part
of
+ /// the register are considered defs and not accounted for here.
SmallDenseMap<unsigned, RegionUsers, 2> Uses;
+
/// This register's rematerializable dependencies, one per unique
- /// rematerializable register operand.
+ /// rematerializable register operand over all definitions.
SmallVector<RegisterIdx, 2> Dependencies;
- /// Returns the rematerializable register from its defining instruction.
+ MachineInstr *getFirstDef() const { return Defs.front(); }
+ MachineInstr *getLastDef() const { return Defs.back(); }
+
+ /// Returns the rematerializable register from one of its defining
+ /// instructions.
Register getDefReg() const {
- assert(DefMI && "defining instruction was deleted");
+ const MachineInstr *DefMI = getFirstDef();
+ assert(DefMI && "defining instruction(s) were deleted");
+ if (!DefMI->getOperand(0).isDef())
+ dbgs() << *DefMI;
assert(DefMI->getOperand(0).isDef() && "not a register def");
----------------
arsenm wrote:
```suggestion
assert(DefMI && DefMI->getOperand(0).isDef() && "not a register def");
```
Stray debug printing
https://github.com/llvm/llvm-project/pull/197580
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