[RISCV][GISEL] Legalize G_VAARG through expansion. (#73065)
G_VAARG can be expanded similiar to SelectionDAG::expandVAArg through
LegalizerHelper::lower. This patch implements the lowering through this
style of expansion.
The expansion gets the head of the va_list by loading the pointer to
va_list. Then, the head of the list is adjusted depending on argument
alignment information. This gives a pointer to the element to be read
out of the va_list. Next, the head of the va_list is bumped to the next
element in the list. The new head of the list is stored back to the
original pointer to the head of the va_list so that subsequent G_VAARG
instructions get the next element in the list. Lastly, the element is
loaded from the alignment adjusted pointer constructed earlier.
This change is stacked on #73062.
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 045fc78..37e7153 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -3793,6 +3793,8 @@
return lowerTRUNC(MI);
GISEL_VECREDUCE_CASES_NONSEQ
return lowerVectorReduction(MI);
+ case G_VAARG:
+ return lowerVAArg(MI);
}
}
@@ -7887,6 +7889,56 @@
return UnableToLegalize;
}
+static Type *getTypeForLLT(LLT Ty, LLVMContext &C);
+
+LegalizerHelper::LegalizeResult LegalizerHelper::lowerVAArg(MachineInstr &MI) {
+ MachineFunction &MF = *MI.getMF();
+ const DataLayout &DL = MIRBuilder.getDataLayout();
+ LLVMContext &Ctx = MF.getFunction().getContext();
+ Register ListPtr = MI.getOperand(1).getReg();
+ LLT PtrTy = MRI.getType(ListPtr);
+
+ // LstPtr is a pointer to the head of the list. Get the address
+ // of the head of the list.
+ Align PtrAlignment = DL.getABITypeAlign(getTypeForLLT(PtrTy, Ctx));
+ MachineMemOperand *PtrLoadMMO = MF.getMachineMemOperand(
+ MachinePointerInfo(), MachineMemOperand::MOLoad, PtrTy, PtrAlignment);
+ auto VAList = MIRBuilder.buildLoad(PtrTy, ListPtr, *PtrLoadMMO).getReg(0);
+
+ const Align A(MI.getOperand(2).getImm());
+ LLT PtrTyAsScalarTy = LLT::scalar(PtrTy.getSizeInBits());
+ if (A > TLI.getMinStackArgumentAlignment()) {
+ Register AlignAmt =
+ MIRBuilder.buildConstant(PtrTyAsScalarTy, A.value() - 1).getReg(0);
+ auto AddDst = MIRBuilder.buildPtrAdd(PtrTy, VAList, AlignAmt);
+ auto AndDst = MIRBuilder.buildMaskLowPtrBits(PtrTy, AddDst, Log2(A));
+ VAList = AndDst.getReg(0);
+ }
+
+ // Increment the pointer, VAList, to the next vaarg
+ // The list should be bumped by the size of element in the current head of
+ // list.
+ Register Dst = MI.getOperand(0).getReg();
+ LLT LLTTy = MRI.getType(Dst);
+ Type *Ty = getTypeForLLT(LLTTy, Ctx);
+ auto IncAmt =
+ MIRBuilder.buildConstant(PtrTyAsScalarTy, DL.getTypeAllocSize(Ty));
+ auto Succ = MIRBuilder.buildPtrAdd(PtrTy, VAList, IncAmt);
+
+ // Store the increment VAList to the legalized pointer
+ MachineMemOperand *StoreMMO = MF.getMachineMemOperand(
+ MachinePointerInfo(), MachineMemOperand::MOStore, PtrTy, PtrAlignment);
+ MIRBuilder.buildStore(Succ, ListPtr, *StoreMMO);
+ // Load the actual argument out of the pointer VAList
+ Align EltAlignment = DL.getABITypeAlign(Ty);
+ MachineMemOperand *EltLoadMMO = MF.getMachineMemOperand(
+ MachinePointerInfo(), MachineMemOperand::MOLoad, LLTTy, EltAlignment);
+ MIRBuilder.buildLoad(Dst, VAList, *EltLoadMMO);
+
+ MI.eraseFromParent();
+ return Legalized;
+}
+
static bool shouldLowerMemFuncForSize(const MachineFunction &MF) {
// On Darwin, -Os means optimize for size without hurting performance, so
// only really optimize for size when -Oz (MinSize) is used.
