[IR] Fix crashes caused by #85592 (#87169)

This patch fixes the crash caused by the pull request:
#85592

Author: elhewaty

llvm/lib/IR/Operator.cpp

@@ -28,8 +28,9 @@ bool Operator::hasPoisonGeneratingFlags() const {
     return OBO->hasNoUnsignedWrap() || OBO->hasNoSignedWrap();
   }
   case Instruction::Trunc: {
-    auto *TI = dyn_cast<TruncInst>(this);
-    return TI->hasNoUnsignedWrap() || TI->hasNoSignedWrap();
+    if (auto *TI = dyn_cast<TruncInst>(this))
+      return TI->hasNoUnsignedWrap() || TI->hasNoSignedWrap();
+    return false;
   }
   case Instruction::UDiv:
   case Instruction::SDiv:

llvm/test/Transforms/FunctionAttrs/noundef.ll

@@ -1,6 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
 ; RUN: opt < %s -passes='function-attrs' -S | FileCheck %s
 
+@g_var = external global [0 x i8]
+
 define i32 @test_ret_constant() {
 ; CHECK-LABEL: define noundef i32 @test_ret_constant(
 ; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
@@ -152,3 +154,15 @@ define i32 @test_ret_constant_msan() sanitize_memory {
 ;
   ret i32 0
 }
+
+define i64 @test_trunc_with_constexpr() {
+; CHECK-LABEL: define noundef i64 @test_trunc_with_constexpr(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 trunc (i64 sub (i64 0, i64 ptrtoint (ptr @g_var to i64)) to i32), 1
+; CHECK-NEXT:    [[CONV:%.*]] = sext i32 [[ADD]] to i64
+; CHECK-NEXT:    ret i64 [[CONV]]
+;
+  %add = add i32 trunc (i64 sub (i64 0, i64 ptrtoint (ptr @g_var to i64)) to i32), 1
+  %conv = sext i32 %add to i64
+  ret i64 %conv
+}