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

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
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This allows us to fold global and constant pool addresses into
load/store during isel instead of in the post-isel peephole. I
did not copy the alignment check for ConsantPoolSDNode because it
wasn't tested.

Remove the now untested GlobalAddressSDNode and ConsantPoolSDNode
handling from the peephole.

I think the only time the peephole is used now is when we split a
constant add into (addi (add X, C1 <https://reviews.llvm.org/C1>), C2). I plan to look at folding
that into SelectAddrRegImm next.


Repository:
  rG LLVM Github Monorepo

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
@@ -1839,10 +1839,37 @@
   if (SelectAddrFrameIndex(Addr, Base, Offset))
     return true;
 
+  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 = GA->getGlobal()->getPointerAlignment(DL);
+          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(),
                                            Subtarget->getXLenVT());
@@ -2213,30 +2240,6 @@
       return false;
     ImmOperand = CurDAG->getTargetConstant(CombinedOffset, SDLoc(ImmOperand),
                                            ImmOperand.getValueType());
-  } else if (auto *GA = dyn_cast<GlobalAddressSDNode>(ImmOperand)) {
-    // If the off1 in (addi base, off1) 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 off1 can overflow the 12 bits.
-    // Check if off2 falls within that margin; if so off1+off2 can't overflow.
-    const DataLayout &DL = CurDAG->getDataLayout();
-    Align Alignment = GA->getGlobal()->getPointerAlignment(DL);
-    if (Offset2 != 0 && Alignment <= Offset2)
-      return false;
-    int64_t Offset1 = GA->getOffset();
-    int64_t CombinedOffset = Offset1 + Offset2;
-    ImmOperand = CurDAG->getTargetGlobalAddress(
-        GA->getGlobal(), SDLoc(ImmOperand), ImmOperand.getValueType(),
-        CombinedOffset, GA->getTargetFlags());
-  } else if (auto *CP = dyn_cast<ConstantPoolSDNode>(ImmOperand)) {
-    // Ditto.
-    Align Alignment = CP->getAlign();
-    if (Offset2 != 0 && Alignment <= Offset2)
-      return false;
-    int64_t Offset1 = CP->getOffset();
-    int64_t CombinedOffset = Offset1 + Offset2;
-    ImmOperand = CurDAG->getTargetConstantPool(
-        CP->getConstVal(), ImmOperand.getValueType(), CP->getAlign(),
-        CombinedOffset, CP->getTargetFlags());
   } else {
     return false;
   }


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