EarlyCSE: fix CmpPredicate duplicate-hashing (#119902)

Strip hash_value() for CmpPredicate, as different callers have different
hashing use-cases. In this case, there is just one caller, namely
EarlyCSE, which calls hash_combine() on a CmpPredicate, which used to
call hash_combine() on a CmpInst::Predicate prior to 4a0d53a
(PatternMatch: migrate to CmpPredicate). This has uncovered a bug where
two icmp instructions differing in just the fact that one of them has
the samesign flag on it are hashed differently, leading to divergent
hashing, and a crash. Fix this crash by dropping samesign information on
icmp instructions before hashing them, preserving the former behavior.

Fixes #119893.

Author: artagnon

llvm/include/llvm/IR/CmpPredicate.h

@@ -71,13 +71,7 @@ class CmpPredicate {
 
   /// Get the swapped predicate of a CmpInst.
   static CmpPredicate getSwapped(const CmpInst *Cmp);
-
-  /// Provided to facilitate storing a CmpPredicate in data structures that
-  /// require hashing.
-  friend hash_code hash_value(const CmpPredicate &Arg); // NOLINT
 };
-
-[[nodiscard]] hash_code hash_value(const CmpPredicate &Arg);
 } // namespace llvm
 
 #endif

llvm/lib/IR/Instructions.cpp

@@ -3946,10 +3946,6 @@ CmpPredicate CmpPredicate::getSwapped(const CmpInst *Cmp) {
   return getSwapped(get(Cmp));
 }
 
-hash_code llvm::hash_value(const CmpPredicate &Arg) { // NOLINT
-  return hash_combine(Arg.Pred, Arg.HasSameSign);
-}
-
 //===----------------------------------------------------------------------===//
 //                        SwitchInst Implementation
 //===----------------------------------------------------------------------===//

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

@@ -290,7 +290,8 @@ static unsigned getHashValueImpl(SimpleValue Val) {
       Pred = CmpInst::getInversePredicate(Pred);
       std::swap(A, B);
     }
-    return hash_combine(Inst->getOpcode(), Pred, X, Y, A, B);
+    return hash_combine(Inst->getOpcode(),
+                        static_cast<CmpInst::Predicate>(Pred), X, Y, A, B);
   }
 
   if (CastInst *CI = dyn_cast<CastInst>(Inst))

llvm/test/Transforms/EarlyCSE/pr119893.ll

@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=early-cse -S %s | FileCheck %s
+
+define i32 @samesign_hash_bug(i16 %v) {
+; CHECK-LABEL: define i32 @samesign_hash_bug(
+; CHECK-SAME: i16 [[V:%.*]]) {
+; CHECK-NEXT:    [[ZEXT:%.*]] = zext i16 [[V]] to i32
+; CHECK-NEXT:    [[ICMP_SAMESIGN:%.*]] = icmp ugt i32 [[ZEXT]], 31
+; CHECK-NEXT:    [[SELECT_ICMP_SAMESIGN:%.*]] = select i1 [[ICMP_SAMESIGN]], i32 0, i32 1
+; CHECK-NEXT:    [[SELECT_ICMP:%.*]] = select i1 [[ICMP_SAMESIGN]], i32 1, i32 0
+; CHECK-NEXT:    ret i32 [[SELECT_ICMP]]
+;
+  %zext = zext i16 %v to i32
+  %icmp.samesign = icmp samesign ugt i32 %zext, 31
+  %select.icmp.samesign = select i1 %icmp.samesign, i32 0, i32 1
+  %ashr = ashr i32 0, %select.icmp.samesign
+  %icmp = icmp ugt i32 %zext, 31
+  %select.icmp = select i1 %icmp, i32 1, i32 0
+  %ret = add i32 %ashr, %select.icmp
+  ret i32 %ret
+}