Increased regBx size from 16 to 24 bits to increase jump range in the VM

from 32K to 8M instructions. Fixes #12727
nim-lang · Dec 8, 2019 · 76228e6 · 76228e6
1 parent 23fc93f
commit 76228e6
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Showing 2 changed files with 16 additions and 2 deletions.
diff --git a/compiler/vmdef.nim b/compiler/vmdef.nim
@@ -12,14 +12,14 @@
 
 import ast, idents, options, modulegraphs, lineinfos
 
-type TInstrType* = uint32
+type TInstrType* = uint64
 
 const
   regOBits = 8 # Opcode
   regABits = 8
   regBBits = 8
   regCBits = 8
-  regBxBits = 16
+  regBxBits = 24
 
   byteExcess* = 128 # we use excess-K for immediates
 

diff --git a/tests/vm/tfarjump.nim b/tests/vm/tfarjump.nim
@@ -0,0 +1,14 @@
+# Test a VM relative jump with an offset larger then 32767 instructions.
+
+import macros
+
+static:
+  var a = 0
+  macro foo(): untyped =
+    let s = newStmtList()
+    for i in 1..6554:
+      s.add nnkCommand.newTree(ident("inc"), ident("a"))
+    quote do:
+      if true:
+        `s`
+  foo()