Make enum iteration with seq safe by default

By default `llvm::seq` would happily iterate over enums, which may be unsafe if the enum values are not continuous. This patch disable enum iteration with `llvm::seq` and `llvm::seq_inclusive` and adds two new functions: `enum_seq` and `enum_seq_inclusive`.

To make sure enum iteration is safe, we require users to declare their enum types as iterable by specializing `enum_iteration_traits<SomeEnum>`. Because it's not always possible to add these traits next to enum definition (e.g., for enums defined in external libraries), we provide an escape hatch to allow iteration on per-callsite basis by passing `force_iteration_on_noniterable_enum`.

The main benefit of this approach is that these global declarations via traits can appear just next to enum definitions, making easy to spot when enums are miss-labeled, e.g., after introducing new enum values, whereas `force_iteration_on_noniterable_enum` should stand out and be easy to grep for.

This emerged from a discussion with gchatelet@ about reusing llvm's `Sequence.h` in lieu of https://github.com/GPUOpen-Drivers/llpc/blob/dev/lgc/interface/lgc/EnumIterator.h.

Reviewed By: dblaikie, gchatelet, aaron.ballman

Differential Revision: https://reviews.llvm.org/D107378

1 files changed, 4 insertions, 8 deletions

diff --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index 7bf7e0b..f88e986 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -1572,8 +1572,7 @@ void ICmpTestImpl(CmpInst::Predicate Pred) {
 }
 
 TEST(ConstantRange, ICmp) {
-  for (auto Pred : seq_inclusive(CmpInst::Predicate::FIRST_ICMP_PREDICATE,
-                                 CmpInst::Predicate::LAST_ICMP_PREDICATE))
+  for (auto Pred : ICmpInst::predicates())
     ICmpTestImpl(Pred);
 }
 
@@ -2531,8 +2530,7 @@ void testConstantRangeICmpPredEquivalence(ICmpInst::Predicate SrcPred, T Func) {
 }
 
 TEST_F(ConstantRangeTest, areInsensitiveToSignednessOfICmpPredicate) {
-  for (auto Pred : seq_inclusive(ICmpInst::Predicate::FIRST_ICMP_PREDICATE,
-                                 ICmpInst::Predicate::LAST_ICMP_PREDICATE)) {
+  for (auto Pred : ICmpInst::predicates()) {
     if (ICmpInst::isEquality(Pred))
       continue;
     ICmpInst::Predicate FlippedSignednessPred =
@@ -2548,8 +2546,7 @@ TEST_F(ConstantRangeTest, areInsensitiveToSignednessOfICmpPredicate) {
 }
 
 TEST_F(ConstantRangeTest, areInsensitiveToSignednessOfInvertedICmpPredicate) {
-  for (auto Pred : seq_inclusive(ICmpInst::Predicate::FIRST_ICMP_PREDICATE,
-                                 ICmpInst::Predicate::LAST_ICMP_PREDICATE)) {
+  for (auto Pred : ICmpInst::predicates()) {
     if (ICmpInst::isEquality(Pred))
       continue;
     ICmpInst::Predicate InvertedFlippedSignednessPred =
@@ -2567,8 +2564,7 @@ TEST_F(ConstantRangeTest, areInsensitiveToSignednessOfInvertedICmpPredicate) {
 }
 
 TEST_F(ConstantRangeTest, getEquivalentPredWithFlippedSignedness) {
-  for (auto Pred : seq_inclusive(ICmpInst::Predicate::FIRST_ICMP_PREDICATE,
-                                 ICmpInst::Predicate::LAST_ICMP_PREDICATE)) {
+  for (auto Pred : ICmpInst::predicates()) {
     if (ICmpInst::isEquality(Pred))
       continue;
     testConstantRangeICmpPredEquivalence(