[PATCH] D126986: [RISCV] Support LUI+ADDIW in doPeepholeLoadStoreADDI.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 434132.
craig.topper added a comment.

Improve comment on the negative test.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126986/new/

https://reviews.llvm.org/D126986

Files:
  llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
  llvm/test/CodeGen/RISCV/fold-addi-loadstore.ll


Index: llvm/test/CodeGen/RISCV/fold-addi-loadstore.ll
===================================================================
--- llvm/test/CodeGen/RISCV/fold-addi-loadstore.ll
+++ llvm/test/CodeGen/RISCV/fold-addi-loadstore.ll
@@ -328,14 +328,16 @@
 ; RV64I-LABEL: load_const_medium:
 ; RV64I:       # %bb.0: # %entry
 ; RV64I-NEXT:    lui a0, 1
-; RV64I-NEXT:    addiw a0, a0, -16
-; RV64I-NEXT:    lw a0, 0(a0)
+; RV64I-NEXT:    lw a0, -16(a0)
 ; RV64I-NEXT:    ret
 entry:
   %0 = load i32, i32* inttoptr (i64 4080 to i32*)
   ret i32 %0
 }
 
+; The constant here is 0x7ffff800, this value requires LUI+ADDIW on RV64,
+; LUI+ADDI would produce a different constant so we can't fold into the load
+; offset.
 define dso_local i32 @load_const_large() nounwind {
 ; RV32I-LABEL: load_const_large:
 ; RV32I:       # %bb.0: # %entry
Index: llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -2233,9 +2233,23 @@
   if (!Base.isMachineOpcode())
     return false;
 
-  // If the base is an ADDI, we can merge it in to the load/store.
-  if (Base.getMachineOpcode() != RISCV::ADDI)
-    return false;
+  if (Base.getMachineOpcode() == RISCV::ADDI) {
+    // If the base is an ADDI, we can merge it in to the load/store.
+  } else if (Base.getMachineOpcode() == RISCV::ADDIW &&
+             isa<ConstantSDNode>(Base.getOperand(1)) &&
+             Base.getOperand(0).isMachineOpcode() &&
+             Base.getOperand(0).getMachineOpcode() == RISCV::LUI &&
+             isa<ConstantSDNode>(Base.getOperand(0).getOperand(0))) {
+    // ADDIW can be merged if it's part of LUI+ADDIW constant materialization
+    // and LUI+ADDI would have produced the same result. This is true for all
+    // simm32 values except 0x7ffff800-0x7fffffff.
+    int64_t Offset =
+      SignExtend64<32>(Base.getOperand(0).getConstantOperandVal(0) << 12);
+    Offset += cast<ConstantSDNode>(Base.getOperand(1))->getSExtValue();
+    if (!isInt<32>(Offset))
+      return false;
+  } else
+   return false;
 
   SDValue ImmOperand = Base.getOperand(1);
   uint64_t Offset2 = N->getConstantOperandVal(OffsetOpIdx);


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