MachineCSE: Update the heuristics for isProfitableToCSE.
If the result of a common subexpression is used at all uses of the candidate
expression, CSE should not increase the live range of the common subexpression.
rdar://11393714 and rdar://11819721
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161396 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp
index 9cfe9ab..0a76f8d 100644
--- a/lib/CodeGen/MachineCSE.cpp
+++ b/lib/CodeGen/MachineCSE.cpp
@@ -324,6 +324,29 @@
MachineInstr *CSMI, MachineInstr *MI) {
// FIXME: Heuristics that works around the lack the live range splitting.
+ // If CSReg is used at all uses of Reg, CSE should not increase register
+ // pressure of CSReg.
+ bool MayIncreasePressure = true;
+ if (TargetRegisterInfo::isVirtualRegister(CSReg) &&
+ TargetRegisterInfo::isVirtualRegister(Reg)) {
+ MayIncreasePressure = false;
+ SmallPtrSet<MachineInstr*, 8> CSUses;
+ for (MachineRegisterInfo::use_nodbg_iterator I =MRI->use_nodbg_begin(CSReg),
+ E = MRI->use_nodbg_end(); I != E; ++I) {
+ MachineInstr *Use = &*I;
+ CSUses.insert(Use);
+ }
+ for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(Reg),
+ E = MRI->use_nodbg_end(); I != E; ++I) {
+ MachineInstr *Use = &*I;
+ if (!CSUses.count(Use)) {
+ MayIncreasePressure = true;
+ break;
+ }
+ }
+ }
+ if (!MayIncreasePressure) return true;
+
// Heuristics #1: Don't CSE "cheap" computation if the def is not local or in
// an immediate predecessor. We don't want to increase register pressure and
// end up causing other computation to be spilled.