Skip the opt on Arm for now

src/coreclr/jit/assertionprop.cpp

@@ -4180,14 +4180,16 @@ GenTree* Compiler::optAssertionProp_ModDiv(ASSERT_VALARG_TP assertions, GenTreeO
         changed = true;
     }
 
+#ifdef TARGET_AMD64
     if (((tree->gtFlags & GTF_UMOD_UINT16_OPERANDS) == 0) && tree->OperIs(GT_UMOD) && op2->IsCnsIntOrI() &&
-        FitsIn<uint16_t>(op2->AsIntCon()->IconValue()) &&
+        FitsIn<uint16_t>(op2->AsIntCon()->IconValue()) && op2->AsIntCon()->IconValue() > 0 &&
         IntegralRange::ForType(TYP_USHORT).Contains(IntegralRange::ForNode(op1, this)))
     {
         JITDUMP("Both operands for UMOD are in uint16 range...\n")
         tree->gtFlags |= GTF_UMOD_UINT16_OPERANDS;
         changed = true;
     }
+#endif
 
     return changed ? optAssertionProp_Update(tree, tree, stmt) : nullptr;
 }

src/coreclr/jit/gentree.h

@@ -540,7 +540,7 @@ enum GenTreeFlags : unsigned int
 
     GTF_DIV_MOD_NO_OVERFLOW     = 0x40000000, // GT_DIV, GT_MOD -- Div or mod definitely does not overflow.
 
-    GTF_UMOD_UINT16_OPERANDS    = 0x80000000, // UMOD -- Both operands to a mod are in uint16 range.
+    GTF_UMOD_UINT16_OPERANDS    = 0x80000000, // UMOD -- Both operands to a mod are in uint16 range. The divisor is non-zero constant.
 
     GTF_CHK_INDEX_INBND         = 0x80000000, // GT_BOUNDS_CHECK -- have proven this check is always in-bounds
 

src/coreclr/jit/lower.cpp

@@ -7184,17 +7184,13 @@ bool Lowering::LowerUnsignedDivOrMod(GenTreeOp* divMod)
 
     assert(divisorValue >= 3);
 
-    if (comp->opts.MinOpts())
-    {
-        return false;
-    }
-
-#if defined(TARGET_64BIT)
+#ifdef TARGET_AMD64
     // Replace (uint16 % uint16) with a cheaper variant of FastMod, specialized for 16-bit operands.
     if ((divMod->gtFlags & GTF_UMOD_UINT16_OPERANDS) != 0)
     {
         assert(!isDiv);
         assert(divisorValue > 0 && divisorValue <= UINT16_MAX);
+        assert(!comp->opts.MinOpts());
 
         // uint multiplier = uint.MaxValue / divisor + 1;
         // ulong result = ((ulong)(dividend * multiplier) * divisor) >> 32;
@@ -7230,11 +7226,11 @@ bool Lowering::LowerUnsignedDivOrMod(GenTreeOp* divMod)
         ContainCheckRange(multiplier, divMod);
         return true;
     }
-#endif
+#endif // TARGET_AMD64
 
 // TODO-ARM-CQ: Currently there's no GT_MULHI for ARM32
 #if defined(TARGET_XARCH) || defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-    if (divisorValue >= 3)
+    if (!comp->opts.MinOpts() && (divisorValue >= 3))
     {
         size_t magic;
         bool   increment;