[AMDGPU] Fix broken uses of isLegalFLATOffset and splitFlatOffset (#147469)

The last parameter of these functions used to be `Signed`, and it looks
like a few calls weren't updated when that was changed to `FlatVariant`.
Effectively, the functions were called with `FlatVariant=SALU` due to
integer promotions, which doesn't make any sense.

Author: ritter-x2a

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -2032,16 +2032,17 @@ bool AMDGPUDAGToDAGISel::SelectScratchSVAddr(SDNode *N, SDValue Addr,
     int64_t COffsetVal = cast<ConstantSDNode>(RHS)->getSExtValue();
     const SIInstrInfo *TII = Subtarget->getInstrInfo();
 
-    if (TII->isLegalFLATOffset(COffsetVal, AMDGPUAS::PRIVATE_ADDRESS, true)) {
+    if (TII->isLegalFLATOffset(COffsetVal, AMDGPUAS::PRIVATE_ADDRESS,
+                               SIInstrFlags::FlatScratch)) {
       Addr = LHS;
       ImmOffset = COffsetVal;
     } else if (!LHS->isDivergent() && COffsetVal > 0) {
       SDLoc SL(N);
       // saddr + large_offset -> saddr + (vaddr = large_offset & ~MaxOffset) +
       //                         (large_offset & MaxOffset);
       int64_t SplitImmOffset, RemainderOffset;
-      std::tie(SplitImmOffset, RemainderOffset)
-        = TII->splitFlatOffset(COffsetVal, AMDGPUAS::PRIVATE_ADDRESS, true);
+      std::tie(SplitImmOffset, RemainderOffset) = TII->splitFlatOffset(
+          COffsetVal, AMDGPUAS::PRIVATE_ADDRESS, SIInstrFlags::FlatScratch);
 
       if (isUInt<32>(RemainderOffset)) {
         SDNode *VMov = CurDAG->getMachineNode(

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -5591,7 +5591,8 @@ AMDGPUInstructionSelector::selectScratchSVAddr(MachineOperand &Root) const {
 
   Register OrigAddr = Addr;
   if (ConstOffset != 0 &&
-      TII.isLegalFLATOffset(ConstOffset, AMDGPUAS::PRIVATE_ADDRESS, true)) {
+      TII.isLegalFLATOffset(ConstOffset, AMDGPUAS::PRIVATE_ADDRESS,
+                            SIInstrFlags::FlatScratch)) {
     Addr = PtrBase;
     ImmOffset = ConstOffset;
   }

llvm/lib/Target/AMDGPU/SIInstrInfo.h

@@ -1448,8 +1448,7 @@ class SIInstrInfo final : public AMDGPUGenInstrInfo {
                         Align Alignment = Align(4)) const;
 
   /// Returns if \p Offset is legal for the subtarget as the offset to a FLAT
-  /// encoded instruction. If \p Signed, this is for an instruction that
-  /// interprets the offset as signed.
+  /// encoded instruction with the given \p FlatVariant.
   bool isLegalFLATOffset(int64_t Offset, unsigned AddrSpace,
                          uint64_t FlatVariant) const;