Change the meaning of 'x' in a transformation

The purpose of this series of commits is to improve code generation
for the Clang compiler.

As a first step we want to change the meaning of 'x' in a
transformation such as:

  operation Literal=q => move Literal x | operation x

Currently, a plain 'x' means reg[0] or x(0), which is the first
element in the X register array. That element is distinct from
r(0) which is a variable in process_main(). Therefore, since r(0)
and x(0) are currently distinct it is fine to use x(0) as a
scratch register.

However, in the next commit we will eliminate the separate variable
for storing the contents of X register zero (thus, x(0) and r(0)
will point to the same location in the X register array). Therefore,
we must use another scratch register in transformation. Redefine
a plain 'x' in a transformation to mean x(1023). Also define
SCRATCH_X_REG so that we can refer to the register by name from
C code.

1 files changed, 1 insertions, 1 deletions

diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 10baab506a..f5f1147261 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -4322,7 +4322,7 @@ gen_has_map_fields(LoaderState* stp, GenOpArg Fail, GenOpArg Src,
     for (i = 0; i < n; i++) {
 	op->a[3+2*i] = Rest[i];
 	op->a[3+2*i+1].type = TAG_x;
-	op->a[3+2*i+1].val = 0;	/* x(0); normally not used */
+	op->a[3+2*i+1].val = SCRATCH_X_REG; /* Ignore result */
     }
     return op;
 }