[patch] Do not use doloop pattern with pragma Unroll

[patch] Do not use doloop pattern with pragma Unroll

[Eric Botcazou]

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Hi,

this fixes the following Ada failure on 64-bit PowerPC:

-FAIL: gnat.dg/unroll4.adb scan-rtl-dump-times loop2_unroll "optimized: loop 
unrolled 7 times" 2

The IVOPTS pass detects a doloop pattern and consequently discombobulates the 
loop sufficiently as to make it hard for the RTL unrolling pass to compute the 
best number of iterations.

Tested on PowerPC64/Linux and x86-64/Linux, OK for the mainline?


2020-09-28  Eric Botcazou  <ebotcazou@adacore.com>

	* tree-ssa-loop-ivopts.c (analyze_and_mark_doloop_use): Bail out if
	the loop is subject to a pragma Unroll with no specific count.

-- 
Eric Botcazou

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diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 5acf044161c..da04dd5ba0a 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -7947,6 +7947,9 @@ analyze_and_mark_doloop_use (struct ivopts_data *data)
   if (!flag_branch_on_count_reg)
     return;
 
+  if (data->current_loop->unroll == USHRT_MAX)
+    return;
+
   if (!generic_predict_doloop_p (data))
     return;