SmallVector<MachineInstr*, 64> Exps;
unsigned CurrVN;
- bool PerformTrivialCoalescing(MachineInstr *MI, MachineBasicBlock *MBB);
+ bool PerformTrivialCopyPropagation(MachineInstr *MI,
+ MachineBasicBlock *MBB);
bool isPhysDefTriviallyDead(unsigned Reg,
MachineBasicBlock::const_iterator I,
MachineBasicBlock::const_iterator E) const;
INITIALIZE_PASS_END(MachineCSE, "machine-cse",
"Machine Common Subexpression Elimination", false, false)
-bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
- MachineBasicBlock *MBB) {
+/// The source register of a COPY machine instruction can be propagated to all
+/// its users, and this propagation could increase the probability of finding
+/// common subexpressions. If the COPY has only one user, the COPY itself can
+/// be removed.
+bool MachineCSE::PerformTrivialCopyPropagation(MachineInstr *MI,
+ MachineBasicBlock *MBB) {
bool Changed = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
- if (!MRI->hasOneNonDBGUse(Reg))
- // Only coalesce single use copies. This ensure the copy will be
- // deleted.
- continue;
+ bool OnlyOneUse = MRI->hasOneNonDBGUse(Reg);
MachineInstr *DefMI = MRI->getVRegDef(Reg);
if (!DefMI->isCopy())
continue;
continue;
DEBUG(dbgs() << "Coalescing: " << *DefMI);
DEBUG(dbgs() << "*** to: " << *MI);
+ // Propagate SrcReg of copies to MI.
MO.setReg(SrcReg);
MRI->clearKillFlags(SrcReg);
- DefMI->eraseFromParent();
- ++NumCoalesces;
+ // Coalesce single use copies.
+ if (OnlyOneUse) {
+ DefMI->eraseFromParent();
+ ++NumCoalesces;
+ }
Changed = true;
}
bool FoundCSE = VNT.count(MI);
if (!FoundCSE) {
- // Look for trivial copy coalescing opportunities.
- if (PerformTrivialCoalescing(MI, MBB)) {
+ // Using trivial copy propagation to find more CSE opportunities.
+ if (PerformTrivialCopyPropagation(MI, MBB)) {
Changed = true;
// After coalescing MI itself may become a copy.
if (MI->isCopyLike())
continue;
+
+ // Try again to see if CSE is possible.
FoundCSE = VNT.count(MI);
}
}
--- /dev/null
+; RUN: llc < %s -mtriple=aarch64-linux-gnuabi -O2 | FileCheck %s
+
+; marked as external to prevent possible optimizations
+@a = external global i32
+@b = external global i32
+@c = external global i32
+@d = external global i32
+@e = external global i32
+
+define void @combine-sign-comparisons-by-cse(i32 *%arg) {
+; CHECK: cmp
+; CHECK: b.ge
+; CHECK-NOT: cmp
+; CHECK: b.le
+
+entry:
+ %a = load i32* @a, align 4
+ %b = load i32* @b, align 4
+ %c = load i32* @c, align 4
+ %d = load i32* @d, align 4
+ %e = load i32* @e, align 4
+
+ %cmp = icmp slt i32 %a, %e
+ br i1 %cmp, label %land.lhs.true, label %lor.lhs.false
+
+land.lhs.true:
+ %cmp1 = icmp eq i32 %b, %c
+ br i1 %cmp1, label %return, label %if.end
+
+lor.lhs.false:
+ %cmp2 = icmp sgt i32 %a, %e
+ br i1 %cmp2, label %land.lhs.true3, label %if.end
+
+land.lhs.true3:
+ %cmp4 = icmp eq i32 %b, %d
+ br i1 %cmp4, label %return, label %if.end
+
+if.end:
+ br label %return
+
+return:
+ %retval.0 = phi i32 [ 0, %if.end ], [ 1, %land.lhs.true3 ], [ 1, %land.lhs.true ]
+ store i32 %a, i32 *%arg
+ ret void
+}