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POINTER_PLUS_EXPR Vs. PLUS_EXPR
- From: a b <blue_3too at hotmail dot com>
- To: gcc gcc <gcc at gcc dot gnu dot org>, <pinskia at gmail dot com>
- Date: Wed, 8 Aug 2012 01:00:34 +0000
- Subject: POINTER_PLUS_EXPR Vs. PLUS_EXPR
I hit a problem about the 2 operands of a addr-plus instruction. My instruction is special because it is not commutative and requries address be the 2nd operand and the offset in the 3rd one. But my port generates PLUS_EXPR instead of POINTER_PLUS_EXPR and finally mistakenly switches the order of the address and offset.
The relevant code is in fold-const.c:
10281 switch (code)
10283 case POINTER_PLUS_EXPR:
10292 /* INT +p INT -> (PTR)(INT + INT). Stripping types allows for this. */
10293 if (INTEGRAL_TYPE_P (TREE_TYPE (arg1))
10294 && INTEGRAL_TYPE_P (TREE_TYPE (arg0)))
10295 return fold_convert_loc (loc, type,
10296 fold_build2_loc (loc, PLUS_EXPR, uintptrtype,
10297 fold_convert_loc (loc, uintptrtype,
10299 fold_convert_loc (loc, uintptrtype,
the code seems to force gcc to generate a PLUS_EXPR instead of POINTER_PLUS_EXPR and I am not clear what is the context for the piece of code.
The code was checked in by Andrew in 2007 (http://gcc.gnu.org/ml/fortran/2007-06/msg00163.html)
Could anybody kindly explain me what was going on with that piece of code?
or more specifically:
1. what does INT +p INT mean? shouldn't POINTER_PLUS_EXPR always better than PLUS_EXPR? why change to PLUS_EXPR?
2. In general, when we should use POINTER_PLUS_EXPR and PLUS_EXPR. I understand the good of POINTER_PLUS_EXPR in my case. but it seems that it is not strictly enforced that address+offset should always represented by POINTER_PLUS_EXPR . Then can anybody tell me what the rule that a POINTER_PLUS_EXPR should be or happens to be used?
Another irlevant question is where I can find the regression test result of the gcc releases such as 4.5/4.7? I try to find out which dejagnu tests have known-failures.