[MIR][MachineCSE] Implementing proper MachineInstr::getNumExplicitDefs()
Apparently, MachineInstr class definition as well as pretty much all of
the machine passes assume that the only kind of MachineInstr's operands
that is variadic for variadic opcodes is explicit non-definitions.
In particular, this assumption is made by MachineInstr::defs(), uses(),
and explicit_uses() methods, as well as by MachineCSE pass.
The assumption is incorrect judging from at least TableGen backend
implementation, that recognizes variable_ops in OutOperandList, and the
very existence of G_UNMERGE_VALUES generic opcode, or ARM load multiple
instructions, all of which have variadic defs.
In particular, MachineCSE pass breaks MIR with CSE'able G_UNMERGE_VALUES
instructions in it.
This commit implements MachineInstr::getNumExplicitDefs() similar to
pre-existing MachineInstr::getNumExplicitOperands(), fixes
MachineInstr::defs(), uses(), and explicit_uses(), and fixes MachineCSE
pass.
As the issue addressed seems to affect only machine passes that could be
ran mid-GlobalISel pipeline at the moment, the other passes aren't fixed
by this commit, like MachineLICM: that could be done on per-pass basis
when (if ever) they get adopted for GlobalISel.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D45640
llvm-svn: 334520
diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index cca4aa8..6c92b1d 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -550,8 +550,7 @@
// Check if it's profitable to perform this CSE.
bool DoCSE = true;
- unsigned NumDefs = MI->getDesc().getNumDefs() +
- MI->getDesc().getNumImplicitDefs();
+ unsigned NumDefs = MI->getNumDefs();
for (unsigned i = 0, e = MI->getNumOperands(); NumDefs && i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);