[InstCombine] Remove the canonicalise SextADD + GEP

Author: LiqinWeng

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -3026,27 +3026,6 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
           GEP, Builder.CreateGEP(GEP.getSourceElementType(), NewPtr, Idx2, "",
                                  IsInBounds));
     }
-    ConstantInt *C;
-    if (match(GEP.getOperand(1), m_OneUse(m_SExtLike(m_OneUse(m_NSWAdd(
-                                     m_Value(Idx1), m_ConstantInt(C))))))) {
-      // %add = add nsw i32 %idx1, idx2
-      // %sidx = sext i32 %add to i64
-      // %gep = getelementptr i32, ptr %ptr, i64 %sidx
-      // as:
-      // %newptr = getelementptr i32, ptr %ptr, i32 %idx1
-      // %newgep = getelementptr i32, ptr %newptr, i32 idx2
-      bool IsInBounds = CanPreserveInBounds(
-          /*IsNSW=*/true, Idx1, C);
-      auto *NewPtr = Builder.CreateGEP(
-          GEP.getSourceElementType(), GEP.getPointerOperand(),
-          Builder.CreateSExt(Idx1, GEP.getOperand(1)->getType()), "",
-          IsInBounds);
-      return replaceInstUsesWith(
-          GEP,
-          Builder.CreateGEP(GEP.getSourceElementType(), NewPtr,
-                            Builder.CreateSExt(C, GEP.getOperand(1)->getType()),
-                            "", IsInBounds));
-    }
   }
 
   if (!GEP.isInBounds()) {

llvm/test/Transforms/InstCombine/array.ll

@@ -86,10 +86,10 @@ define ptr @test_zero_sext_add_nsw(ptr %base, i32 %a) {
 ; CHECK-SAME: ptr [[BASE:%.*]], i32 [[A:%.*]]) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
-; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[A]] to i64
+; CHECK-NEXT:    [[INDEX:%.*]] = add nsw i32 [[A]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[INDEX]] to i64
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i32, ptr [[P1]], i64 [[TMP0]]
-; CHECK-NEXT:    [[P2:%.*]] = getelementptr i8, ptr [[TMP1]], i64 4
-; CHECK-NEXT:    ret ptr [[P2]]
+; CHECK-NEXT:    ret ptr [[TMP1]]
 ;
 entry:
   %p1 = getelementptr i8, ptr %base, i64 -4