Introduce ORIGINAL_REGNO macro

From-SVN: r38546

1 files changed, 4 insertions, 6 deletions

diff --git a/gcc/rtl.def b/gcc/rtl.def
index fcad7ec..6f0aec8 100644
--- a/gcc/rtl.def
+++ b/gcc/rtl.def
@@ -583,12 +583,10 @@ DEF_RTL_EXPR(VALUE, "value", "0", 'o')
 /* A register.  The "operand" is the register number, accessed with
    the REGNO macro.  If this number is less than FIRST_PSEUDO_REGISTER
    than a hardware register is being referred to.  The second operand
-   doesn't really exist.  Unfortunately, however, the compiler
-   implicitly assumes that a REG can be transformed in place into a
-   MEM, and therefore that a REG is at least as big as a MEM.  To
-   avoid this memory overhead, which is likely to be substantial,
-   search for uses of PUT_CODE that turn REGs into MEMs, and fix them
-   somehow.  Then, the trailing `0' can be removed here.  */
+   holds the original register number - this will be different for a
+   pseudo register that got turned into a hard register.
+   This rtx needs to have as many (or more) fields as a MEM, since we
+   can change REG rtx's into MEMs during reload.  */
 DEF_RTL_EXPR(REG, "reg", "i0", 'o')
 
 /* A scratch register.  This represents a register used only within a