[InstCombine] Extract logic for "emit offset and rewrite gep" (NFC)

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -2050,9 +2050,9 @@ Instruction *InstCombinerImpl::visitPtrToInt(PtrToIntInst &CI) {
     // the GEP otherwise.
     if (GEP->hasOneUse() &&
         isa<ConstantPointerNull>(GEP->getPointerOperand())) {
-      return replaceInstUsesWith(CI,
-                                 Builder.CreateIntCast(EmitGEPOffset(GEP), Ty,
-                                                       /*isSigned=*/false));
+      return replaceInstUsesWith(
+          CI, Builder.CreateIntCast(EmitGEPOffset(cast<GEPOperator>(GEP)), Ty,
+                                    /*isSigned=*/false));
     }
   }
 

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -816,29 +816,9 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
     }
 
     if (GEPsInBounds || CmpInst::isEquality(Cond)) {
-      auto EmitGEPOffsetAndRewrite = [&](GEPOperator *GEP) {
-        IRBuilderBase::InsertPointGuard Guard(Builder);
-        auto *Inst = dyn_cast<Instruction>(GEP);
-        if (Inst)
-          Builder.SetInsertPoint(Inst);
-
-        Value *Offset = EmitGEPOffset(GEP);
-        // If a non-trivial GEP has other uses, rewrite it to avoid duplicating
-        // the offset arithmetic.
-        if (Inst && !GEP->hasOneUse() && !GEP->hasAllConstantIndices() &&
-            !GEP->getSourceElementType()->isIntegerTy(8)) {
-          replaceInstUsesWith(*Inst,
-                              Builder.CreateGEP(Builder.getInt8Ty(),
-                                                GEP->getPointerOperand(),
-                                                Offset, "", GEPsInBounds));
-          eraseInstFromFunction(*Inst);
-        }
-        return Offset;
-      };
-
       // ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2)  --->  (OFFSET1 cmp OFFSET2)
-      Value *L = EmitGEPOffsetAndRewrite(GEPLHS);
-      Value *R = EmitGEPOffsetAndRewrite(GEPRHS);
+      Value *L = EmitGEPOffset(GEPLHS, /*RewriteGEP=*/true);
+      Value *R = EmitGEPOffset(GEPRHS, /*RewriteGEP=*/true);
       return new ICmpInst(ICmpInst::getSignedPredicate(Cond), L, R);
     }
   }

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -376,7 +376,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
     }
   }
 
-  Value *EmitGEPOffset(User *GEP);
+  Value *EmitGEPOffset(GEPOperator *GEP, bool RewriteGEP = false);
   Instruction *scalarizePHI(ExtractElementInst &EI, PHINode *PN);
   Instruction *foldBitcastExtElt(ExtractElementInst &ExtElt);
   Instruction *foldCastedBitwiseLogic(BinaryOperator &I);

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -190,8 +190,26 @@ bool InstCombiner::isValidAddrSpaceCast(unsigned FromAS, unsigned ToAS) const {
   return TTI.isValidAddrSpaceCast(FromAS, ToAS);
 }
 
-Value *InstCombinerImpl::EmitGEPOffset(User *GEP) {
-  return llvm::emitGEPOffset(&Builder, DL, GEP);
+Value *InstCombinerImpl::EmitGEPOffset(GEPOperator *GEP, bool RewriteGEP) {
+  if (!RewriteGEP)
+    return llvm::emitGEPOffset(&Builder, DL, GEP);
+
+  IRBuilderBase::InsertPointGuard Guard(Builder);
+  auto *Inst = dyn_cast<Instruction>(GEP);
+  if (Inst)
+    Builder.SetInsertPoint(Inst);
+
+  Value *Offset = EmitGEPOffset(GEP);
+  // If a non-trivial GEP has other uses, rewrite it to avoid duplicating
+  // the offset arithmetic.
+  if (Inst && !GEP->hasOneUse() && !GEP->hasAllConstantIndices() &&
+      !GEP->getSourceElementType()->isIntegerTy(8)) {
+    replaceInstUsesWith(
+        *Inst, Builder.CreateGEP(Builder.getInt8Ty(), GEP->getPointerOperand(),
+                                 Offset, "", GEP->isInBounds()));
+    eraseInstFromFunction(*Inst);
+  }
+  return Offset;
 }
 
 /// Legal integers and common types are considered desirable. This is used to