Remove constant special case

With the new expansion this would have to be more careful about
a constant on multi-use GEP and non-constant on merged one-use
GEPs. Just drop this heuristic for now.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2147,27 +2147,22 @@ CommonPointerBase CommonPointerBase::compute(Value *LHS, Value *RHS) {
 }
 
 bool CommonPointerBase::isExpensive() const {
-  bool SeenConst = false;
   unsigned NumGEPs = 0;
-  auto ProcessGEPs = [&SeenConst, &NumGEPs](ArrayRef<GEPOperator *> GEPs) {
+  auto ProcessGEPs = [&NumGEPs](ArrayRef<GEPOperator *> GEPs) {
     bool SeenMultiUse = false;
     for (GEPOperator *GEP : GEPs) {
       // Only count multi-use GEPs, excluding the first one. For the first one,
       // we will directly reuse the offset. For one-use GEPs, their offset will
       // be folded into a multi-use GEP.
       if (!GEP->hasOneUse()) {
-        if (SeenMultiUse) {
-          bool IsConst = GEP->hasAllConstantIndices();
-          SeenConst |= IsConst;
-          NumGEPs += !IsConst;
-        }
+        if (SeenMultiUse)
+          ++NumGEPs;
         SeenMultiUse = true;
       }
     }
   };
   ProcessGEPs(LHSGEPs);
   ProcessGEPs(RHSGEPs);
-  NumGEPs += SeenConst;
   return NumGEPs > 2;
 }
 

llvm/test/Transforms/InstCombine/icmp-gep.ll

@@ -932,21 +932,17 @@ define i1 @gep_multiple_multi_use_below_limit_extra_one_use_gep2(ptr %base, i64
   ret i1 %cmp
 }
 
-define i1 @gep_multiple_multi_use_below_limit_consts(ptr %base, i64 %idx1, i64 %idx2) {
-; CHECK-LABEL: @gep_multiple_multi_use_below_limit_consts(
+define i1 @gep_multiple_multi_above_below_limit_consts(ptr %base, i64 %idx1, i64 %idx2) {
+; CHECK-LABEL: @gep_multiple_multi_above_below_limit_consts(
 ; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr i8, ptr [[BASE:%.*]], i64 16
 ; CHECK-NEXT:    call void @use(ptr [[GEP1]])
-; CHECK-NEXT:    [[GEP4_IDX:%.*]] = shl i64 [[IDX2:%.*]], 2
-; CHECK-NEXT:    [[GEP4:%.*]] = getelementptr i8, ptr [[GEP1]], i64 [[GEP4_IDX]]
-; CHECK-NEXT:    call void @use(ptr [[GEP4]])
-; CHECK-NEXT:    [[GEP3:%.*]] = getelementptr i8, ptr [[GEP4]], i64 16
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr i32, ptr [[GEP1]], i64 [[IDX1:%.*]]
+; CHECK-NEXT:    call void @use(ptr [[GEP2]])
+; CHECK-NEXT:    [[GEP3:%.*]] = getelementptr i8, ptr [[GEP2]], i64 16
 ; CHECK-NEXT:    call void @use(ptr [[GEP3]])
-; CHECK-NEXT:    [[GEP4_IDX1:%.*]] = shl i64 [[IDX3:%.*]], 2
-; CHECK-NEXT:    [[GEP5:%.*]] = getelementptr i8, ptr [[GEP3]], i64 [[GEP4_IDX1]]
-; CHECK-NEXT:    call void @use(ptr [[GEP5]])
-; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[GEP4_IDX]], 32
-; CHECK-NEXT:    [[TMP2:%.*]] = sub i64 0, [[GEP4_IDX1]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[GEP4:%.*]] = getelementptr i32, ptr [[GEP3]], i64 [[IDX2:%.*]]
+; CHECK-NEXT:    call void @use(ptr [[GEP4]])
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr [[GEP4]], [[BASE]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %gep1 = getelementptr i32, ptr %base, i64 4