Avoid extra vreg copies for arguments passed in registers. Specifically, this can make MachineCSE more effective in some cases (especially in small functions). PR8361 / part of rdar://problem/8259436 .
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130928 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index b02a7b6..c69be7b 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -6232,6 +6232,25 @@
#include "llvm/CodeGen/SelectionDAGISel.h"
+/// isOnlyUsedInEntryBlock - If the specified argument is only used in the
+/// entry block, return true. This includes arguments used by switches, since
+/// the switch may expand into multiple basic blocks.
+static bool isOnlyUsedInEntryBlock(const Argument *A) {
+ // With FastISel active, we may be splitting blocks, so force creation
+ // of virtual registers for all non-dead arguments.
+ if (EnableFastISel)
+ return A->use_empty();
+
+ const BasicBlock *Entry = A->getParent()->begin();
+ for (Value::const_use_iterator UI = A->use_begin(), E = A->use_end();
+ UI != E; ++UI) {
+ const User *U = *UI;
+ if (cast<Instruction>(U)->getParent() != Entry || isa<SwitchInst>(U))
+ return false; // Use not in entry block.
+ }
+ return true;
+}
+
void SelectionDAGISel::LowerArguments(const BasicBlock *LLVMBB) {
// If this is the entry block, emit arguments.
const Function &F = *LLVMBB->getParent();
@@ -6375,8 +6394,8 @@
if (I->use_empty() && NumValues)
SDB->setUnusedArgValue(I, InVals[i]);
- for (unsigned Value = 0; Value != NumValues; ++Value) {
- EVT VT = ValueVTs[Value];
+ for (unsigned Val = 0; Val != NumValues; ++Val) {
+ EVT VT = ValueVTs[Val];
EVT PartVT = TLI.getRegisterType(*CurDAG->getContext(), VT);
unsigned NumParts = TLI.getNumRegisters(*CurDAG->getContext(), VT);
@@ -6395,21 +6414,34 @@
i += NumParts;
}
+ // We don't need to do anything else for unused arguments.
+ if (ArgValues.empty())
+ continue;
+
// Note down frame index for byval arguments.
- if (I->hasByValAttr() && !ArgValues.empty())
+ if (I->hasByValAttr())
if (FrameIndexSDNode *FI =
dyn_cast<FrameIndexSDNode>(ArgValues[0].getNode()))
FuncInfo->setByValArgumentFrameIndex(I, FI->getIndex());
- if (!I->use_empty()) {
- SDValue Res;
- if (!ArgValues.empty())
- Res = DAG.getMergeValues(&ArgValues[0], NumValues,
- SDB->getCurDebugLoc());
- SDB->setValue(I, Res);
+ SDValue Res = DAG.getMergeValues(&ArgValues[0], NumValues,
+ SDB->getCurDebugLoc());
+ SDB->setValue(I, Res);
- // If this argument is live outside of the entry block, insert a copy from
- // wherever we got it to the vreg that other BB's will reference it as.
+ // If this argument is live outside of the entry block, insert a copy from
+ // wherever we got it to the vreg that other BB's will reference it as.
+ if (Res.getOpcode() == ISD::CopyFromReg) {
+ // If we can, though, try to skip creating an unnecessary vreg.
+ // FIXME: This isn't very clean... it would be nice to make this more
+ // general.
+ unsigned Reg = cast<RegisterSDNode>(Res.getOperand(1))->getReg();
+ if (TargetRegisterInfo::isVirtualRegister(Reg)) {
+ FuncInfo->ValueMap[I] = Reg;
+ continue;
+ }
+ }
+ if (!isOnlyUsedInEntryBlock(I)) {
+ FuncInfo->InitializeRegForValue(I);
SDB->CopyToExportRegsIfNeeded(I);
}
}