diff --git a/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-idxsize.ll b/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-idxsize.ll
new file mode 100644
index 0000000000000..3fb2789ce0e49
--- /dev/null
+++ b/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-idxsize.ll
@@ -0,0 +1,262 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=lower-constant-intrinsics -S < %s | FileCheck %s
+
+; Some extra tests using 16-bit pointers and 16-bit index type size. This
+; allows us to for example test what happens when the index type used in a
+; getelementptr does not match with the index type size (e.g. when not running
+; full opt pipeline before the lower-constant-intrinsics pass).
+
+target datalayout = "e-p:16:16:16"
+
+
+define i32 @possible_out_of_bounds_gep_i8(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i8(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i8 2, i8 10
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i8 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 3, i32 0
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i8 2, i8 10
+  %ptr.slide = getelementptr i8, ptr %obj, i8 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+define i32 @possible_out_of_bounds_gep_i16(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i16(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i16 2, i16 10
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i16 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 3, i32 0
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i16 2, i16 10
+  %ptr.slide = getelementptr i8, ptr %obj, i16 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+define i32 @possible_out_of_bounds_gep_i32(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i32(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i32 2, i32 10
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i32 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 3, i32 0
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i32 2, i32 10
+  %ptr.slide = getelementptr i8, ptr %obj, i32 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+; SROA would produce IR like this if applied to @possible_out_of_bounds_gep_i16.
+; FIXME: The %objsize_min result here is invalid.
+define i32 @possible_out_of_bounds_gep_i16_sroa(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i16_sroa(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[DOTSROA_GEP:%.*]] = getelementptr i8, ptr [[OBJ]], i16 2
+; CHECK-NEXT:    [[DOTSROA_GEP1:%.*]] = getelementptr i8, ptr [[OBJ]], i16 10
+; CHECK-NEXT:    [[OFFSET_SROA_SEL:%.*]] = select i1 [[C0]], ptr [[DOTSROA_GEP]], ptr [[DOTSROA_GEP1]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 3, i32 65531
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8], align 1
+  %.sroa.gep = getelementptr i8, ptr %obj, i16 2
+  %.sroa.gep1 = getelementptr i8, ptr %obj, i16 10
+  %offset.sroa.sel = select i1 %c0, ptr %.sroa.gep, ptr %.sroa.gep1
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %offset.sroa.sel, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %offset.sroa.sel, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+; Indices are truncated to the pointer size in a gep. So "i32 -65526" should
+; be treated as "i16 10" and we expect same result as for
+; @possible_out_of_bounds_gep_i16 above.
+; FIXME: The result here is incorrect (max/min is swapped).
+define i32 @possible_out_of_bounds_gep_i32_trunc(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i32_trunc(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i32 2, i32 -65526
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i32 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 0, i32 3
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i32 2, i32 -65526  ; 0xffff000a
+  %ptr.slide = getelementptr i8, ptr %obj, i32 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+define i32 @out_of_bounds_gep_i8(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @out_of_bounds_gep_i8(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i8 -128
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 -1, i32 0
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %ptr.slide = getelementptr i8, ptr %obj, i8 -128
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+define i32 @out_of_bounds_gep_i32(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @out_of_bounds_gep_i32(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i32 10
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %obj = alloca [5 x i8]
+  %ptr.slide = getelementptr i8, ptr %obj, i32 10
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+define i32 @out_of_bounds_gep_i32_trunc(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @out_of_bounds_gep_i32_trunc(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i32 -65526
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %obj = alloca [5 x i8]
+  %ptr.slide = getelementptr i8, ptr %obj, i32 -65526
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+; In this test the index will be out-of-bounds, but the current analysis won't
+; detect that. The analysis will find out that %offset is in the range [-2,
+; 10] which includes valid offsets that aren't out-of-bounds. Therefore we can
+; expect to get -1 for %objsize_max even if an advanced analysis should be
+; able to derive that we are out-of-bounds (returning 0 also for
+; %objsize_max).
+define i32 @out_of_bounds_gep_i16_pos_neg(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @out_of_bounds_gep_i16_pos_neg(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i32 10, i32 -2
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i32 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 -1, i32 0
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i32 10, i32 -2
+  %ptr.slide = getelementptr i8, ptr %obj, i32 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+; With 16-bit index size %offset is either 32767 or -32768. Thus, when
+; aggregating the possible offsets it we know that it is in the range [-32768,
+; 32767], which includes valid offsets that aren't out-of-bounds. This is
+; similar to the out_of_bounds_gep_i16_pos_neg test above, and the current
+; implementation is expected to derive the result -1 for %objsize_max.
+define i32 @out_of_bounds_gep_i32_trunc_select(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @out_of_bounds_gep_i32_trunc_select(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i32 32767, i32 32768
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i32 [[OFFSET]]
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i32 32767, i32 32768
+  %ptr.slide = getelementptr i8, ptr %obj, i32 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+; FIXME: Is 3 really correct for %objsize_min here?
+define i32 @possible_out_of_bounds_gep_i8_neg(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i8_neg(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i8 2, i8 -10
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i8 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 -1, i32 3
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i8 2, i8 -10
+  %ptr.slide = getelementptr i8, ptr %obj, i8 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
+
+; FIXME: Is 3 really correct for %objsize_min here?
+define i32 @possible_out_of_bounds_gep_i16_neg(i1 %c0, i1 %c1) {
+; CHECK-LABEL: define i32 @possible_out_of_bounds_gep_i16_neg(
+; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OBJ:%.*]] = alloca [5 x i8], align 1
+; CHECK-NEXT:    [[OFFSET:%.*]] = select i1 [[C0]], i16 2, i16 -10
+; CHECK-NEXT:    [[PTR_SLIDE:%.*]] = getelementptr i8, ptr [[OBJ]], i16 [[OFFSET]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C1]], i32 -1, i32 3
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %obj = alloca [5 x i8]
+  %offset = select i1 %c0, i16 2, i16 -10
+  %ptr.slide = getelementptr i8, ptr %obj, i16 %offset
+  %objsize_max = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 false, i1 true, i1 false)
+  %objsize_min = call i32 @llvm.objectsize.i32.p0(ptr %ptr.slide, i1 true, i1 true, i1 false)
+  %res = select i1 %c1, i32 %objsize_max, i32 %objsize_min
+  ret i32 %res
+}
diff --git a/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-phi.ll b/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-phi.ll
index 564311da64a81..d294650d7f3e2 100644
--- a/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-phi.ll
+++ b/llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-phi.ll
@@ -200,8 +200,12 @@ if.end:
   ret i64 %size
 }
 
-define i64 @pick_negative_offset_different_width(i32 %n) {
-; CHECK-LABEL: @pick_negative_offset_different_width(
+; FIXME: The result here looks weird. Either we reference into buffer0 with an
+;        oob offset. Or we reference buffer1 (8 bytes) with a 4 byte
+;        offset. The result 5 is wrong in both cases. Probably better to
+;        return -1 here since we do not know if we have an oob pointer.
+define i64 @pick_negative_offset_different_width_index_maybe_too_small(i32 %n, i1 %c) {
+; CHECK-LABEL: @pick_negative_offset_different_width_index_maybe_too_small(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[BUFFER0:%.*]] = alloca i8, i64 4, align 1
 ; CHECK-NEXT:    [[BUFFER1:%.*]] = alloca i8, i64 8, align 1
@@ -216,7 +220,8 @@ define i64 @pick_negative_offset_different_width(i32 %n) {
 ; CHECK:       if.end:
 ; CHECK-NEXT:    [[P:%.*]] = phi ptr [ [[OFFSETED0]], [[IF_ELSE]] ], [ [[OFFSETED1]], [[IF_END]] ]
 ; CHECK-NEXT:    [[POFFSETED:%.*]] = getelementptr i8, ptr [[P]], i64 -2
-; CHECK-NEXT:    ret i64 5
+; CHECK-NEXT:    [[SIZE:%.*]] = select i1 [[C:%.*]], i64 5, i64 0
+; CHECK-NEXT:    ret i64 [[SIZE]]
 ;
 entry:
   %buffer0 = alloca i8, i64 4
@@ -235,7 +240,51 @@ if.else:
 if.end:
   %p = phi ptr [ %offseted0, %if.then ], [ %offseted1, %if.else ]
   %poffseted = getelementptr i8, ptr %p, i64 -2
-  %size = call i64 @llvm.objectsize.i64.p0(ptr %poffseted, i1 false, i1 false, i1 false)
+  %sizemax = call i64 @llvm.objectsize.i64.p0(ptr %poffseted, i1 false, i1 false, i1 false)
+  %sizemin = call i64 @llvm.objectsize.i64.p0(ptr %poffseted, i1 true, i1 false, i1 false)
+  %size = select i1 %c, i64 %sizemax, i64 %sizemin
+  ret i64 %size
+}
+
+define i64 @pick_negative_offset_different_width_index_maybe_too_large(i32 %n, i1 %c) {
+; CHECK-LABEL: @pick_negative_offset_different_width_index_maybe_too_large(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[BUFFER0:%.*]] = alloca i8, i64 4, align 1
+; CHECK-NEXT:    [[BUFFER1:%.*]] = alloca i8, i64 8, align 1
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[N:%.*]], 0
+; CHECK-NEXT:    br i1 [[COND]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[OFFSETED0:%.*]] = getelementptr i8, ptr [[BUFFER0]], i64 1
+; CHECK-NEXT:    br label [[IF_END:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    [[OFFSETED1:%.*]] = getelementptr i8, ptr [[BUFFER1]], i64 6
+; CHECK-NEXT:    br label [[IF_END]]
+; CHECK:       if.end:
+; CHECK-NEXT:    [[P:%.*]] = phi ptr [ [[OFFSETED0]], [[IF_THEN]] ], [ [[OFFSETED1]], [[IF_ELSE]] ]
+; CHECK-NEXT:    [[POFFSETED:%.*]] = getelementptr i8, ptr [[P]], i64 2
+; CHECK-NEXT:    [[SIZE:%.*]] = select i1 [[C:%.*]], i64 1, i64 0
+; CHECK-NEXT:    ret i64 [[SIZE]]
+;
+entry:
+  %buffer0 = alloca i8, i64 4
+  %buffer1 = alloca i8, i64 8
+  %cond = icmp eq i32 %n, 0
+  br i1 %cond, label %if.then, label %if.else
+
+if.then:
+  %offseted0 = getelementptr i8, ptr %buffer0, i64 1
+  br label %if.end
+
+if.else:
+  %offseted1 = getelementptr i8, ptr %buffer1, i64 6
+  br label %if.end
+
+if.end:
+  %p = phi ptr [ %offseted0, %if.then ], [ %offseted1, %if.else ]
+  %poffseted = getelementptr i8, ptr %p, i64 2
+  %sizemax = call i64 @llvm.objectsize.i64.p0(ptr %poffseted, i1 false, i1 false, i1 false)
+  %sizemin = call i64 @llvm.objectsize.i64.p0(ptr %poffseted, i1 true, i1 false, i1 false)
+  %size = select i1 %c, i64 %sizemax, i64 %sizemin
   ret i64 %size
 }