Subreg promotion not happening for the test case

[Vineet Gupta]

Hi Jeff, Robin,

This morning I was talking about the following test where subreg 
promoted is not being generated during expand, whereas for RISC-V 
ABI/ISA it should.

gcc.c-torture/compile/20070121.c -Os -march=rv64gc -mabi=lp64d

expand_gimple_basic_block
     expand_gimple_stmt
...
         expand_expr_real
...
              case SSA_NAME:
                   if (REG_P (decl_rtl)
                       && dmode != BLKmode
                       && GET_MODE (decl_rtl) != dmode)

Here it seems to be taking promote_ssa_mode () codepath and not 
promote_function_mode

Do note this only happens for -Os. Tree dump is same for both -Os and 
-O2, Expand for -Os misses setting the subreg promoted.

Thx,
-Vineet