8336912: G1: Undefined behavior for G1ConfidencePercent=0

Reviewed-by: ayang, sangheki

Author: Thomas Schatzl

src/hotspot/share/gc/g1/g1_globals.hpp

@@ -112,7 +112,7 @@
                                                                             \
   product(uint, G1ConfidencePercent, 50,                                    \
           "Confidence level for MMU/pause predictions")                     \
-          range(0, 100)                                                     \
+          range(1, 100)                                                     \
                                                                             \
   product(uintx, G1SummarizeRSetStatsPeriod, 0, DIAGNOSTIC,                 \
           "The period (in number of GCs) at which we will generate "        \

test/hotspot/jtreg/gc/arguments/TestG1PercentageOptions.java

@@ -51,14 +51,14 @@ private static final class OptionDescription {
         }
     }
 
-    private static final String[] defaultValid = new String[] {
-        "0", "1", "50", "95", "100" };
-    private static final String[] defaultInvalid = new String[] {
-        "-10", "110", "bad" };
+    private static final String[] rangeOneToHundredValid = new String[] {
+        "1", "50", "95", "100" };
+    private static final String[] rangeOneToHundredInvalid = new String[] {
+        "0", "-10", "110", "bad" };
 
     // All of the G1 product arguments that are percentages.
     private static final OptionDescription[] percentOptions = new OptionDescription[] {
-        new OptionDescription("G1ConfidencePercent", defaultValid, defaultInvalid)
+        new OptionDescription("G1ConfidencePercent", rangeOneToHundredValid, rangeOneToHundredInvalid)
         // Other percentage options are not yet validated by argument processing.
     };