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Re: Fix PR rtl-optimization/84071
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Wed, 31 Jan 2018 16:02:07 +0100
- Subject: Re: Fix PR rtl-optimization/84071
- Authentication-results: sourceware.org; auth=none
- References: <17052335.8sCGlW3d3s@polaris>
> Tested on SPARC64/Linux and ARM/EABI, applied on mainline and 7 branch.
As discussed in the audit trail, this beefs up the internal documentation
about WORD_REGISTER_OPERATIONS.
Tested with 'make doc', applied on mainline and 7 branch.
2018-01-31 Eric Botcazou <ebotcazou@adacore.com>
PR rtl-optimization/84071
* doc/tm.texi.in (WORD_REGISTER_OPERATIONS): Add explicit case.
* doc/tm.texi: Regenerate.
--
Eric Botcazou
Index: doc/tm.texi.in
===================================================================
--- doc/tm.texi.in (revision 257227)
+++ doc/tm.texi.in (working copy)
@@ -7376,8 +7376,12 @@ is in effect.
@defmac WORD_REGISTER_OPERATIONS
Define this macro to 1 if operations between registers with integral mode
-smaller than a word are always performed on the entire register.
-Most RISC machines have this property and most CISC machines do not.
+smaller than a word are always performed on the entire register. To be
+more explicit, if you start with a pair of @code{word_mode} registers with
+known values and you do a subword, for example @code{QImode}, addition on
+the low part of the registers, then the compiler may consider that the
+result has a known value in @code{word_mode} too if the macro is defined
+to 1. Most RISC machines have this property and most CISC machines do not.
@end defmac
@hook TARGET_MIN_ARITHMETIC_PRECISION