[PATCH] D128738: [RISCV] Match RISCVISD::ADD_LO in SelectAddrRegImm.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 441866.
craig.topper added a comment.

Use commonAlignment to match the recent change to the post-isel peephole.
Don't delete any code from the post-isel peephole.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128738/new/

https://reviews.llvm.org/D128738

Files:
  llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp


Index: llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -1873,10 +1873,38 @@
   SDLoc DL(Addr);
   MVT VT = Addr.getSimpleValueType();
 
+  if (Addr.getOpcode() == RISCVISD::ADD_LO) {
+    Base = Addr.getOperand(0);
+    Offset = Addr.getOperand(1);
+    return true;
+  }
+
   if (CurDAG->isBaseWithConstantOffset(Addr)) {
     int64_t CVal = cast<ConstantSDNode>(Addr.getOperand(1))->getSExtValue();
     if (isInt<12>(CVal)) {
       Base = Addr.getOperand(0);
+      if (Base.getOpcode() == RISCVISD::ADD_LO) {
+        SDValue LoOperand = Base.getOperand(1);
+        if (auto *GA = dyn_cast<GlobalAddressSDNode>(LoOperand)) {
+          // If the Lo in (ADD_LO hi, lo) is a global variable's address
+          // (its low part, really), then we can rely on the alignment of that
+          // variable to provide a margin of safety before low part can overflow
+          // the 12 bits of the load/store offset. Check if CVal falls within
+          // that margin; if so (low part + CVal) can't overflow.
+          const DataLayout &DL = CurDAG->getDataLayout();
+          Align Alignment = commonAlignment(
+              GA->getGlobal()->getPointerAlignment(DL), GA->getOffset());
+          if (CVal == 0 || Alignment > CVal) {
+            int64_t CombinedOffset = CVal + GA->getOffset();
+            Base = Base.getOperand(0);
+            Offset = CurDAG->getTargetGlobalAddress(
+                GA->getGlobal(), SDLoc(LoOperand), LoOperand.getValueType(),
+                CombinedOffset, GA->getTargetFlags());
+            return true;
+          }
+        }
+      }
+
       if (auto *FIN = dyn_cast<FrameIndexSDNode>(Base))
         Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), VT);
       Offset = CurDAG->getTargetConstant(CVal, DL, VT);


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