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If two-address def is dead and the instruction does not define other registers, and it doesn't produce side effects, just delete the instruction.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65218 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2009-02-21 03:14:25 +00:00
parent d9fb712403
commit 28c7ce3fd4
2 changed files with 73 additions and 0 deletions
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30
lib/CodeGen/TwoAddressInstructionPass.cpp
View File

@ -53,6 +53,7 @@ STATISTIC(NumAggrCommuted , "Number of instructions aggressively commuted");
STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address");
STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk");
STATISTIC(NumReMats, "Number of instructions re-materialized");
STATISTIC(NumDeletes, "Number of dead instructions deleted");
namespace {
class VISIBILITY_HIDDEN TwoAddressInstructionPass
@ -371,6 +372,26 @@ TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi,
return true;
}
/// isSafeToDelete - If the specified instruction does not produce any side
/// effects and all of its defs are dead, then it's safe to delete.
static bool isSafeToDelete(MachineInstr *MI, const TargetInstrInfo *TII) {
const TargetInstrDesc &TID = MI->getDesc();
if (TID.mayStore() || TID.isCall())
return false;
if (TID.isTerminator() || TID.hasUnmodeledSideEffects())
return false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
if (!MO.isDead())
return false;
}
return true;
}
/// runOnMachineFunction - Reduce two-address instructions to two operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
@ -450,6 +471,15 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
// allow us to coalesce A and B together, eliminating the copy we are
// about to insert.
if (!mi->killsRegister(regB)) {
// If regA is dead and the instruction can be deleted, just delete
// it so it doesn't clobber regB.
if (mi->getOperand(ti).isDead() && isSafeToDelete(mi, TII)) {
mbbi->erase(mi); // Nuke the old inst.
mi = nmi;
++NumDeletes;
break; // Done with this instruction.
}
// If this instruction is commutative, check to see if C dies. If
// so, swap the B and C operands. This makes the live ranges of A
// and C joinable.

43
test/CodeGen/X86/twoaddr-delete.ll Normal file
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@ -0,0 +1,43 @@
; RUN: llvm-as < %s | llc -march=x86 -stats |& grep {twoaddrinstr} | grep {Number of dead instructions deleted}
%struct.anon = type { [3 x double], double, %struct.node*, [64 x %struct.bnode*], [64 x %struct.bnode*] }
%struct.bnode = type { i16, double, [3 x double], i32, i32, [3 x double], [3 x double], [3 x double], double, %struct.bnode*, %struct.bnode* }
%struct.node = type { i16, double, [3 x double], i32, i32 }
define i32 @main(i32 %argc, i8** nocapture %argv) nounwind {
entry:
%0 = malloc %struct.anon ; <%struct.anon*> [#uses=2]
%1 = getelementptr %struct.anon* %0, i32 0, i32 2 ; <%struct.node**> [#uses=1]
br label %bb14.i
bb14.i: ; preds = %bb14.i, %entry
%i8.0.reg2mem.0.i = phi i32 [ 0, %entry ], [ %2, %bb14.i ] ; <i32> [#uses=1]
%2 = add i32 %i8.0.reg2mem.0.i, 1 ; <i32> [#uses=2]
%exitcond74.i = icmp eq i32 %2, 32 ; <i1> [#uses=1]
br i1 %exitcond74.i, label %bb32.i, label %bb14.i
bb32.i: ; preds = %bb32.i, %bb14.i
%tmp.0.reg2mem.0.i = phi i32 [ %indvar.next63.i, %bb32.i ], [ 0, %bb14.i ] ; <i32> [#uses=1]
%indvar.next63.i = add i32 %tmp.0.reg2mem.0.i, 1 ; <i32> [#uses=2]
%exitcond64.i = icmp eq i32 %indvar.next63.i, 64 ; <i1> [#uses=1]
br i1 %exitcond64.i, label %bb47.loopexit.i, label %bb32.i
bb.i.i: ; preds = %bb47.loopexit.i
unreachable
stepsystem.exit.i: ; preds = %bb47.loopexit.i
store %struct.node* null, %struct.node** %1, align 4
br label %bb.i6.i
bb.i6.i: ; preds = %bb.i6.i, %stepsystem.exit.i
br i1 false, label %bb107.i.i, label %bb.i6.i
bb107.i.i: ; preds = %bb107.i.i, %bb.i6.i
%q_addr.0.i.i.in = phi %struct.bnode** [ null, %bb107.i.i ], [ %3, %bb.i6.i ] ; <%struct.bnode**> [#uses=0]
br label %bb107.i.i
bb47.loopexit.i: ; preds = %bb32.i
%3 = getelementptr %struct.anon* %0, i32 0, i32 4, i32 0 ; <%struct.bnode**> [#uses=1]
%4 = icmp eq %struct.node* null, null ; <i1> [#uses=1]
br i1 %4, label %stepsystem.exit.i, label %bb.i.i
}