Accept null smallestCompareWidth in caonicalizations.

* `ConditiionalNode.canonical` should accept `null` and go through
  `CanonicalizerTool.smallestCompareWidth` instead of directly querying
  the `LoweringProvider`.
* The neutral `null` value is used in platform-independent contexts.

Author: gilles-duboscq

compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/nodes/calc/ConditionalNode.java

@@ -126,10 +126,13 @@ public ValueNode canonical(CanonicalizerTool tool) {
             return result;
         }
 
-        if (tool != null && stamp instanceof IntegerStamp integerStamp && integerStamp.getBits() >= tool.getLowerer().smallestCompareWidth()) {
-            ValueNode minMaxSynonym = MinMaxNode.fromConditional(condition, trueValue, falseValue, view);
-            if (minMaxSynonym != null) {
-                return minMaxSynonym;
+        if (tool != null && stamp instanceof IntegerStamp integerStamp) {
+            Integer smallestCompareWidth = tool.smallestCompareWidth();
+            if (smallestCompareWidth != null && integerStamp.getBits() >= smallestCompareWidth) {
+                ValueNode minMaxSynonym = MinMaxNode.fromConditional(condition, trueValue, falseValue, view);
+                if (minMaxSynonym != null) {
+                    return minMaxSynonym;
+                }
             }
         }
 

compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/nodes/calc/MinMaxNode.java

@@ -300,8 +300,9 @@ private static boolean equalOrOffBy1(Signedness signedness, ValueNode a, ValueNo
      */
     protected static ValueNode maybeExtendForCompare(ValueNode value, LoweringProvider lowerer, Signedness signedness) {
         Stamp fromStamp = value.stamp(NodeView.DEFAULT);
-        if (fromStamp instanceof PrimitiveStamp && PrimitiveStamp.getBits(fromStamp) < lowerer.smallestCompareWidth()) {
-            Stamp toStamp = IntegerStamp.create(lowerer.smallestCompareWidth());
+        Integer smallestCompareWidth = lowerer.smallestCompareWidth();
+        if (fromStamp instanceof PrimitiveStamp && smallestCompareWidth != null && PrimitiveStamp.getBits(fromStamp) < smallestCompareWidth) {
+            Stamp toStamp = IntegerStamp.create(smallestCompareWidth);
             boolean zeroExtend = (signedness == Signedness.UNSIGNED);
             return IntegerConvertNode.convert(value, toStamp, zeroExtend, NodeView.DEFAULT);
         }

compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/nodes/spi/LoweringProvider.java

@@ -53,7 +53,9 @@ public interface LoweringProvider {
     ValueNode reconstructArrayIndex(JavaKind elementKind, AddressNode address);
 
     /**
-     * Indicates the smallest width for comparing an integer value on the target platform.
+     * Indicates the smallest width for comparing an integer value on the target platform. Returns
+     * {@code null} when this information is not available. This can be the case when this lowering
+     * provider is being used in a platform independent context (e.g., canonicalization).
      */
     Integer smallestCompareWidth();