constantInstruction() & DynamicConstantDesc

[Michael van Acken]

I just started to move my most recent Clojure compiler iteration to
the Classfile API.  It is a pleasure to use.  I appreciate the huge
amount of work that is going into this.

While going through my constant handling tests I found three issues.

First, I expected ConstantDescs.NULL to be mapped to ACONST_NULL.  I
can just as well special case this in the compiler, of course.

Second, to get a test case for the literal constant -0.0 to round-trip
I had to patch CodeBuilder.java to go via LDC:

   cause: expected not equivalent to actual value
expected: [(LDC2_W   -0.0) (DRETURN)]
  actual: [(DCONST_0     ) (DRETURN)]

Third, a round-trip involving the describeConstable() of a Character
instance (via ConstantDescs.BSM_EXPLICIT_CAST) was read back as a DCD
with a nameAndType of "_":"LC;" instead of the expected "_":"C".
Changing the ofCanonical invocation in ConcreteEntry.java fixed this
particular case for me, but I am only fishing around here.

The patch below has more details.

-- mva


diff --git a/src/java.base/share/classes/jdk/classfile/CodeBuilder.java
b/src/java.base/share/classes/jdk/classfile/CodeBuilder.java
index 154050ae8b4..330980af725 100755
--- a/src/java.base/share/classes/jdk/classfile/CodeBuilder.java
+++ b/src/java.base/share/classes/jdk/classfile/CodeBuilder.java
@@ -27,6 +27,7 @@ package jdk.classfile;

 import java.lang.constant.ClassDesc;
 import java.lang.constant.ConstantDesc;
+import java.lang.constant.ConstantDescs;
 import java.lang.constant.DirectMethodHandleDesc;
 import java.lang.constant.DynamicCallSiteDesc;
 import java.lang.constant.MethodTypeDesc;
@@ -424,7 +425,7 @@ public sealed interface CodeBuilder

     default CodeBuilder constantInstruction(ConstantDesc value) {
         // This method must ensure any call to constant(Opcode,
ConstantDesc) has a non-null Opcode.
-        if (value == null) {
+        if (value == null || ConstantDescs.NULL.equals(value)) {
             return constantInstruction(Opcode.ACONST_NULL, null);
         }
         else if (value instanceof Integer iVal) {
@@ -437,16 +438,16 @@ public sealed interface CodeBuilder
             else
                 return constantInstruction(Opcode.LDC2_W, lVal);
         } else if (value instanceof Float fVal) {
-            if (fVal == 0.0)
+            if (fVal.compareTo(0.0f) == 0) // 0.0f but not -0.0f
                 return
with(ConstantInstruction.ofIntrinsic(Opcode.FCONST_0));
-            else if (fVal == 1.0)
+            else if (fVal == 1.0f)
                 return
with(ConstantInstruction.ofIntrinsic(Opcode.FCONST_1));
-            else if (fVal == 2.0)
+            else if (fVal == 2.0f)
                 return
with(ConstantInstruction.ofIntrinsic(Opcode.FCONST_2));
             else
                 return constantInstruction(Opcode.LDC, fVal);
         } else if (value instanceof Double dVal) {
-            if (dVal == 0.0d)
+            if (dVal.compareTo(0.0d) == 0) // 0.0d but not -0.0d
                 return
with(ConstantInstruction.ofIntrinsic(Opcode.DCONST_0));
             else if (dVal == 1.0d)
                 return
with(ConstantInstruction.ofIntrinsic(Opcode.DCONST_1));
diff --git
a/src/java.base/share/classes/jdk/classfile/impl/ConcreteEntry.java
b/src/java.base/share/classes/jdk/classfile/impl/ConcreteEntry.java
index bead58d7618..9dcc8eeb7e1 100755
--- a/src/java.base/share/classes/jdk/classfile/impl/ConcreteEntry.java
+++ b/src/java.base/share/classes/jdk/classfile/impl/ConcreteEntry.java
@@ -797,7 +797,7 @@ public abstract sealed class ConcreteEntry {
                 staticArgs[i] = args.get(i).constantValue();

             return
DynamicConstantDesc.ofCanonical(bootstrap().bootstrapMethod().asSymbol(),
-
nameAndType().name().stringValue(),
ClassDesc.of(Util.toClassString(Util.descriptorToClass(nameAndType().type().stringValue()))),
staticArgs);
+
nameAndType().name().stringValue(),
ClassDesc.ofDescriptor(nameAndType().type().stringValue()), staticArgs);
         }
     }
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