[PATCH] D126843: [RISCV] Support (addi (addi globaladdr, C1), C2) in RISCVMergeBaseOffset.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
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Add with immediates in the range [-4096, -2049] or [2048, 4095] get
convert to two ADDIs. Teach RISCVMergeBaseOffset to recognize this
pattern as well.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126843

Files:
  llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
  llvm/test/CodeGen/RISCV/hoist-global-addr-base.ll


Index: llvm/test/CodeGen/RISCV/hoist-global-addr-base.ll
===================================================================
--- llvm/test/CodeGen/RISCV/hoist-global-addr-base.ll
+++ llvm/test/CodeGen/RISCV/hoist-global-addr-base.ll
@@ -248,3 +248,21 @@
 ; RV64-NEXT:    ret
     ret i8* getelementptr inbounds ([0 x i8], [0 x i8]* @bar, i32 0, i64 -2147485013)
 }
+
+define i8* @offset_addi_addi() {
+; CHECK-LABEL: offset_addi_addi:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a0, %hi(bar+3211)
+; CHECK-NEXT:    addi a0, a0, %lo(bar+3211)
+; CHECK-NEXT:    ret
+    ret i8* getelementptr inbounds ([0 x i8], [0 x i8]* @bar, i32 0, i64 3211)
+}
+
+define i8* @offset_addi_addi_neg() {
+; CHECK-LABEL: offset_addi_addi_neg:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a0, %hi(bar-4000)
+; CHECK-NEXT:    addi a0, a0, %lo(bar-4000)
+; CHECK-NEXT:    ret
+    ret i8* getelementptr inbounds ([0 x i8], [0 x i8]* @bar, i32 0, i64 -4000)
+}
Index: llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
+++ llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
@@ -206,6 +206,19 @@
   case RISCV::ADDI: {
     // Offset is simply an immediate operand.
     int64_t Offset = Tail.getOperand(2).getImm();
+
+    // We might have two ADDIs in a row.
+    Register TailDestReg = Tail.getOperand(0).getReg();
+    if (MRI->hasOneUse(TailDestReg)) {
+      MachineInstr &TailTail = *MRI->use_instr_begin(TailDestReg);
+      if (TailTail.getOpcode() == RISCV::ADDI) {
+        Offset += TailTail.getOperand(2).getImm();
+        DeadInstrs.insert(&Tail);
+        foldOffset(HiLUI, LoADDI, TailTail, Offset);
+        return true;
+      }
+    }
+
     LLVM_DEBUG(dbgs() << "  Offset Instr: " << Tail);
     foldOffset(HiLUI, LoADDI, Tail, Offset);
     return true;


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