8253721: Flag -XX:AVX3Threshold does not accept Zero value

Reviewed-by: kvn, thartmann

Author: Jatin Bhateja

src/hotspot/cpu/x86/globals_x86.hpp

@@ -213,6 +213,7 @@ define_pd_global(intx, InitArrayShortSize, 8*BytesPerLong);
              "for copy, inflate and fill. When this value is set as zero"   \
              "compare operations can also use AVX512 intrinsics.")          \
              range(0, max_jint)                                             \
+             constraint(AVX3ThresholdConstraintFunc,AfterErgo)              \
                                                                             \
   product(bool, IntelJccErratumMitigation, true, DIAGNOSTIC,                \
              "Turn off JVM mitigations related to Intel micro code "        \

src/hotspot/cpu/x86/vm_version_x86.cpp

@@ -1162,13 +1162,6 @@ void VM_Version::get_processor_features() {
   }
 #endif // COMPILER2 && ASSERT
 
-  if (!FLAG_IS_DEFAULT(AVX3Threshold)) {
-    if (!is_power_of_2(AVX3Threshold)) {
-      warning("AVX3Threshold must be a power of 2");
-      FLAG_SET_DEFAULT(AVX3Threshold, 4096);
-    }
-  }
-
 #ifdef _LP64
   if (FLAG_IS_DEFAULT(UseMultiplyToLenIntrinsic)) {
     UseMultiplyToLenIntrinsic = true;

src/hotspot/share/runtime/flags/jvmFlagConstraintsCompiler.cpp

@@ -285,6 +285,17 @@ JVMFlag::Error ArraycopyDstPrefetchDistanceConstraintFunc(uintx value, bool verb
   return JVMFlag::SUCCESS;
 }
 
+JVMFlag::Error AVX3ThresholdConstraintFunc(int value, bool verbose) {
+  if (value != 0 && !is_power_of_2(value)) {
+    JVMFlag::printError(verbose,
+                        "AVX3Threshold ( %d ) must be 0 or "
+                        "a power of two value between 0 and MAX_INT\n", value);
+    return JVMFlag::VIOLATES_CONSTRAINT;
+  }
+
+  return JVMFlag::SUCCESS;
+}
+
 JVMFlag::Error ArraycopySrcPrefetchDistanceConstraintFunc(uintx value, bool verbose) {
   if (value >= 4032) {
     JVMFlag::printError(verbose,

src/hotspot/share/runtime/flags/jvmFlagConstraintsCompiler.hpp

@@ -47,6 +47,7 @@
   f(intx,  OptoLoopAlignmentConstraintFunc)             \
   f(uintx, ArraycopyDstPrefetchDistanceConstraintFunc)  \
   f(uintx, ArraycopySrcPrefetchDistanceConstraintFunc)  \
+  f(int,   AVX3ThresholdConstraintFunc)                 \
   f(uintx, TypeProfileLevelConstraintFunc)              \
   f(intx,  InitArrayShortSizeConstraintFunc)            \
   f(int ,  RTMTotalCountIncrRateConstraintFunc)         \

src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.lir.amd64/src/org/graalvm/compiler/lir/amd64/AMD64ArrayCompareToOp.java

@@ -84,7 +84,6 @@ public final class AMD64ArrayCompareToOp extends AMD64LIRInstruction {
     public AMD64ArrayCompareToOp(LIRGeneratorTool tool, int useAVX3Threshold, JavaKind kind1, JavaKind kind2, Value result, Value array1, Value array2, Value length1, Value length2) {
         super(TYPE);
 
-        assert CodeUtil.isPowerOf2(useAVX3Threshold) : "AVX3Threshold must be power of 2";
         this.useAVX3Threshold = useAVX3Threshold;
         this.kind1 = kind1;
         this.kind2 = kind2;

src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.lir.amd64/src/org/graalvm/compiler/lir/amd64/AMD64StringLatin1InflateOp.java

@@ -71,7 +71,6 @@ public final class AMD64StringLatin1InflateOp extends AMD64LIRInstruction {
     public AMD64StringLatin1InflateOp(LIRGeneratorTool tool, int useAVX3Threshold, Value src, Value dst, Value len) {
         super(TYPE);
 
-        assert CodeUtil.isPowerOf2(useAVX3Threshold) : "AVX3Threshold must be power of 2";
         this.useAVX3Threshold = useAVX3Threshold;
 
         assert asRegister(src).equals(rsi);

src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.lir.amd64/src/org/graalvm/compiler/lir/amd64/AMD64StringUTF16CompressOp.java

@@ -76,7 +76,6 @@ public final class AMD64StringUTF16CompressOp extends AMD64LIRInstruction {
     public AMD64StringUTF16CompressOp(LIRGeneratorTool tool, int useAVX3Threshold, Value res, Value src, Value dst, Value len) {
         super(TYPE);
 
-        assert CodeUtil.isPowerOf2(useAVX3Threshold) : "AVX3Threshold must be power of 2";
         this.useAVX3Threshold = useAVX3Threshold;
 
         assert asRegister(src).equals(rsi);