Improve handling of stack accesses in Thumb-1
Thumb-1 only allows SP-based LDR and STR to be word-sized, and SP-base LDR,
STR, and ADD only allow offsets that are a multiple of 4. Make some changes
to better make use of these instructions:
* Use word loads for anyext byte and halfword loads from the stack.
* Enforce 4-byte alignment on objects accessed in this way, to ensure that
the offset is valid.
* Do the same for objects whose frame index is used, in order to avoid having
to use more than one ADD to generate the frame index.
* Correct how many bits of offset we think AddrModeT1_s has.
Patch by John Brawn.
llvm-svn: 230496
diff --git a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
index 77464bd..6ebf640 100644
--- a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
+++ b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
@@ -1197,6 +1197,11 @@
SDValue &Base, SDValue &OffImm) {
if (N.getOpcode() == ISD::FrameIndex) {
int FI = cast<FrameIndexSDNode>(N)->getIndex();
+ // Only multiples of 4 are allowed for the offset, so the frame object
+ // alignment must be at least 4.
+ MachineFrameInfo *MFI = MF->getFrameInfo();
+ if (MFI->getObjectAlignment(FI) < 4)
+ MFI->setObjectAlignment(FI, 4);
Base = CurDAG->getTargetFrameIndex(FI, TLI->getPointerTy());
OffImm = CurDAG->getTargetConstant(0, MVT::i32);
return true;
@@ -1214,6 +1219,11 @@
Base = N.getOperand(0);
if (Base.getOpcode() == ISD::FrameIndex) {
int FI = cast<FrameIndexSDNode>(Base)->getIndex();
+ // For LHS+RHS to result in an offset that's a multiple of 4 the object
+ // indexed by the LHS must be 4-byte aligned.
+ MachineFrameInfo *MFI = MF->getFrameInfo();
+ if (MFI->getObjectAlignment(FI) < 4)
+ MFI->setObjectAlignment(FI, 4);
Base = CurDAG->getTargetFrameIndex(FI, TLI->getPointerTy());
}
OffImm = CurDAG->getTargetConstant(RHSC, MVT::i32);
@@ -2502,6 +2512,11 @@
int FI = cast<FrameIndexSDNode>(N)->getIndex();
SDValue TFI = CurDAG->getTargetFrameIndex(FI, TLI->getPointerTy());
if (Subtarget->isThumb1Only()) {
+ // Set the alignment of the frame object to 4, to avoid having to generate
+ // more than one ADD
+ MachineFrameInfo *MFI = MF->getFrameInfo();
+ if (MFI->getObjectAlignment(FI) < 4)
+ MFI->setObjectAlignment(FI, 4);
return CurDAG->SelectNodeTo(N, ARM::tADDframe, MVT::i32, TFI,
CurDAG->getTargetConstant(0, MVT::i32));
} else {