[PATCH, GCC/LRA, gcc-5/6-branch] Fix PR78617: Fix conflict detection in rematerialization

[Thomas Preudhomme]

Hi,

Is it ok to backport the fix for PR78617 (incorrect conflict detection in 
rematerialization) to GCC 5 and GCC 6? The patch applies cleanly and the 
testsuite showed no regression when performed with the following configurations:

- an arm-none-eabi GCC cross-compiler targeting Cortex-M0 and Cortex-M3
- a bootstrapped arm-linux-gnueabihf GCC native compiler
- a bootstrapped x86_64-linux-gnu GCC native compiler

ChangeLog entry is as follows:

*** gcc/ChangeLog ***

2017-01-03 Thomas Preud'homme <thomas.preudhomme@arm.com>

         Backport from mainline
         2016-12-07 Thomas Preud'homme <thomas.preudhomme@arm.com>

         PR rtl-optimization/78617
         * lra-remat.c (do_remat): Initialize live_hard_regs from live in
         registers, also setting hard registers mapped to pseudo registers.


*** gcc/testsuite/ChangeLog ***


2017-01-03 Thomas Preud'homme <thomas.preudhomme@arm.com>

         Backport from mainline
         2016-12-07 Thomas Preud'homme <thomas.preudhomme@arm.com>

         PR rtl-optimization/78617
         * gcc.c-torture/execute/pr78617.c: New test.


Best regards,

Thomas
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