[LoongArch] Add option for merge base offset pass

Add `loongarch-enable-merge-offset` option to allow disabling the
`MergeBaseOffset` pass when using optimization.

Reviewers: SixWeining, heiher

Reviewed By: SixWeining, heiher

Pull Request: #161063

Author: wangleiat

llvm/lib/Target/LoongArch/LoongArchTargetMachine.cpp

@@ -57,6 +57,11 @@ static cl::opt<bool>
                            cl::desc("Enable the loop data prefetch pass"),
                            cl::init(false));
 
+static cl::opt<bool>
+    EnableMergeBaseOffset("loongarch-enable-merge-offset",
+                          cl::desc("Enable the merge base offset pass"),
+                          cl::init(true), cl::Hidden);
+
 static Reloc::Model getEffectiveRelocModel(const Triple &TT,
                                            std::optional<Reloc::Model> RM) {
   return RM.value_or(Reloc::Static);
@@ -214,7 +219,7 @@ void LoongArchPassConfig::addMachineSSAOptimization() {
 
 void LoongArchPassConfig::addPreRegAlloc() {
   addPass(createLoongArchPreRAExpandPseudoPass());
-  if (TM->getOptLevel() != CodeGenOptLevel::None)
+  if (TM->getOptLevel() != CodeGenOptLevel::None && EnableMergeBaseOffset)
     addPass(createLoongArchMergeBaseOffsetOptPass());
 }
 

llvm/test/CodeGen/LoongArch/merge-offset-option.ll

@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc --mtriple=loongarch64 -mattr=+d --relocation-model=static -O1 \
+; RUN:     < %s | FileCheck %s --check-prefix=MERGE
+; RUN: llc --mtriple=loongarch64 -mattr=+d --relocation-model=static -O1 \
+; RUN:     --loongarch-enable-merge-offset=false < %s | FileCheck %s --check-prefix=NO_MERGE
+
+@g = dso_local global i32 zeroinitializer, align 4
+
+define void @foo() nounwind {
+; MERGE-LABEL: foo:
+; MERGE:       # %bb.0:
+; MERGE-NEXT:    pcalau12i $a0, %pc_hi20(g)
+; MERGE-NEXT:    ld.w $zero, $a0, %pc_lo12(g)
+; MERGE-NEXT:    ret
+;
+; NO_MERGE-LABEL: foo:
+; NO_MERGE:       # %bb.0:
+; NO_MERGE-NEXT:    pcalau12i $a0, %pc_hi20(g)
+; NO_MERGE-NEXT:    addi.d $a0, $a0, %pc_lo12(g)
+; NO_MERGE-NEXT:    ld.w $zero, $a0, 0
+; NO_MERGE-NEXT:    ret
+  %v = load volatile i32, ptr @g
+  ret void
+}