[Stack realignment] Handling of aligned allocas.
This patch implements dynamic realignment of stack objects for targets
with a non-realigned stack pointer. Behaviour in FunctionLoweringInfo
is changed so that for a target that has StackRealignable set to
false, over-aligned static allocas are considered to be variable-sized
objects and are handled with DYNAMIC_STACKALLOC nodes.
It would be good to group aligned allocas into a single big alloca as
an optimization, but this is yet todo.
SystemZ benefits from this, due to its stack frame layout.
New tests SystemZ/alloca-03.ll for aligned allocas, and
SystemZ/alloca-04.ll for "no-realign-stack" attribute on functions.
Review and help from Ulrich Weigand and Hal Finkel.
llvm-svn: 254227
diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index 9eeb046..e1b20d0 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -48,7 +48,8 @@
SystemZFrameLowering::SystemZFrameLowering()
: TargetFrameLowering(TargetFrameLowering::StackGrowsDown, 8,
- -SystemZMC::CallFrameSize, 8) {
+ -SystemZMC::CallFrameSize, 8,
+ false /* StackRealignable */) {
// Create a mapping from register number to save slot offset.
RegSpillOffsets.grow(SystemZ::NUM_TARGET_REGS);
for (unsigned I = 0, E = array_lengthof(SpillOffsetTable); I != E; ++I)
diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index fa9ee6e..5959e90 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -2739,17 +2739,37 @@
SDValue SystemZTargetLowering::
lowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const {
+ const TargetFrameLowering *TFI = Subtarget.getFrameLowering();
+ bool RealignOpt = !DAG.getMachineFunction().getFunction()->
+ hasFnAttribute("no-realign-stack");
+
SDValue Chain = Op.getOperand(0);
SDValue Size = Op.getOperand(1);
+ SDValue Align = Op.getOperand(2);
SDLoc DL(Op);
+ // If user has set the no alignment function attribute, ignore
+ // alloca alignments.
+ uint64_t AlignVal = (RealignOpt ?
+ dyn_cast<ConstantSDNode>(Align)->getZExtValue() : 0);
+
+ uint64_t StackAlign = TFI->getStackAlignment();
+ uint64_t RequiredAlign = std::max(AlignVal, StackAlign);
+ uint64_t ExtraAlignSpace = RequiredAlign - StackAlign;
+
unsigned SPReg = getStackPointerRegisterToSaveRestore();
+ SDValue NeededSpace = Size;
// Get a reference to the stack pointer.
SDValue OldSP = DAG.getCopyFromReg(Chain, DL, SPReg, MVT::i64);
+ // Add extra space for alignment if needed.
+ if (ExtraAlignSpace)
+ NeededSpace = DAG.getNode(ISD::ADD, DL, MVT::i64, NeededSpace,
+ DAG.getConstant(ExtraAlignSpace, DL, MVT::i64));
+
// Get the new stack pointer value.
- SDValue NewSP = DAG.getNode(ISD::SUB, DL, MVT::i64, OldSP, Size);
+ SDValue NewSP = DAG.getNode(ISD::SUB, DL, MVT::i64, OldSP, NeededSpace);
// Copy the new stack pointer back.
Chain = DAG.getCopyToReg(Chain, DL, SPReg, NewSP);
@@ -2760,6 +2780,16 @@
SDValue ArgAdjust = DAG.getNode(SystemZISD::ADJDYNALLOC, DL, MVT::i64);
SDValue Result = DAG.getNode(ISD::ADD, DL, MVT::i64, NewSP, ArgAdjust);
+ // Dynamically realign if needed.
+ if (RequiredAlign > StackAlign) {
+ Result =
+ DAG.getNode(ISD::ADD, DL, MVT::i64, Result,
+ DAG.getConstant(ExtraAlignSpace, DL, MVT::i64));
+ Result =
+ DAG.getNode(ISD::AND, DL, MVT::i64, Result,
+ DAG.getConstant(~(RequiredAlign - 1), DL, MVT::i64));
+ }
+
SDValue Ops[2] = { Result, Chain };
return DAG.getMergeValues(Ops, DL);
}