[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/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 8d42dce..ff0ccd4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -87,6 +87,7 @@
TLI = MF->getSubtarget().getTargetLowering();
RegInfo = &MF->getRegInfo();
MachineModuleInfo &MMI = MF->getMMI();
+ const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
// Check whether the function can return without sret-demotion.
SmallVector<ISD::OutputArg, 4> Outs;
@@ -103,28 +104,29 @@
for (BasicBlock::const_iterator I = BB->begin(), E = BB->end();
I != E; ++I) {
if (const AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
- // Static allocas can be folded into the initial stack frame adjustment.
- if (AI->isStaticAlloca()) {
+ Type *Ty = AI->getAllocatedType();
+ unsigned Align =
+ std::max((unsigned)MF->getDataLayout().getPrefTypeAlignment(Ty),
+ AI->getAlignment());
+ unsigned StackAlign = TFI->getStackAlignment();
+
+ // Static allocas can be folded into the initial stack frame
+ // adjustment. For targets that don't realign the stack, don't
+ // do this if there is an extra alignment requirement.
+ if (AI->isStaticAlloca() &&
+ (TFI->isStackRealignable() || (Align <= StackAlign))) {
const ConstantInt *CUI = cast<ConstantInt>(AI->getArraySize());
- Type *Ty = AI->getAllocatedType();
uint64_t TySize = MF->getDataLayout().getTypeAllocSize(Ty);
- unsigned Align =
- std::max((unsigned)MF->getDataLayout().getPrefTypeAlignment(Ty),
- AI->getAlignment());
TySize *= CUI->getZExtValue(); // Get total allocated size.
if (TySize == 0) TySize = 1; // Don't create zero-sized stack objects.
StaticAllocaMap[AI] =
MF->getFrameInfo()->CreateStackObject(TySize, Align, false, AI);
-
} else {
- unsigned Align =
- std::max((unsigned)MF->getDataLayout().getPrefTypeAlignment(
- AI->getAllocatedType()),
- AI->getAlignment());
- unsigned StackAlign =
- MF->getSubtarget().getFrameLowering()->getStackAlignment();
+ // FIXME: Overaligned static allocas should be grouped into
+ // a single dynamic allocation instead of using a separate
+ // stack allocation for each one.
if (Align <= StackAlign)
Align = 0;
// Inform the Frame Information that we have variable-sized objects.