Hi,

this patch rotates the loop generated in the prologue to do stack checking 
when -fstack-check is specified, thereby saving one branch instruction.  It 
was initially implemented as a WHILE loop to match the generic implementation 
but can be turned into a DO-WHILE loop because the amount of stack to be 
checked is known at compile time (since it's the static part of the frame).

The patch also changes a mov+sub pair into an lea in the common case on Linux, 
saving one more instruction in the process.

Tested on x86/Linux & x86-64/Linux (ix86_adjust_stack_and_probe path) and 
x86/Solaris (ix86_emit_probe_stack_range path).  OK for the mainline?


2015-11-12  Eric Botcazou  <ebotcazou@adacore.com>

	* config/i386/i386.c (ix86_adjust_stack_and_probe): Adjust and use
	an lea instruction when possible.
	(output_adjust_stack_and_probe): Rotate the loop and simplify.
	(ix86_emit_probe_stack_range): Adjust.
	(output_probe_stack_range): Rotate the loop and simplify.

-- 
Eric Botcazou