From: Martin Jambor <mjambor@suse.cz>
Date: Tue, 12 Sep 2023 17:22:37 +0000 (+0200)
Subject: math-opts: Add dbgcounter for FMA formation
X-Git-Tag: basepoints/gcc-15~6233
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=27e2e7c93e48bcbb63877cc5964fae8dba47d706;p=thirdparty%2Fgcc.git

math-opts: Add dbgcounter for FMA formation

This patch is a simple addition of a debug counter to FMA formation in
tree-ssa-math-opts.cc.  Given that issues with FMAs do occasionally
pop up, it seems genuinely useful.

I simply added an if right after the initial checks in
convert_mult_to_fma even though when FMA formation deferring is
active (i.e. when targeting Zen CPUs) this would interact with it (and
at this moment lead to producing all deferred candidates), so when
using the dbg counter to find a harmful set of FMAs, it is probably
best to also set param_avoid_fma_max_bits to zero.  I could not find a
better place which would not also make the code unnecessarily more
complicated.

gcc/ChangeLog:

2023-09-06  Martin Jambor  <mjambor@suse.cz>

	* dbgcnt.def (form_fma): New.
	* tree-ssa-math-opts.cc: Include dbgcnt.h.
	(convert_mult_to_fma): Bail out if the debug counter say so.
---

diff --git a/gcc/dbgcnt.def b/gcc/dbgcnt.def
index 9e2f1d857b49..871cbf75d931 100644
--- a/gcc/dbgcnt.def
+++ b/gcc/dbgcnt.def
@@ -162,6 +162,7 @@ DEBUG_COUNTER (dom_unreachable_edges)
 DEBUG_COUNTER (dse)
 DEBUG_COUNTER (dse1)
 DEBUG_COUNTER (dse2)
+DEBUG_COUNTER (form_fma)
 DEBUG_COUNTER (gcse2_delete)
 DEBUG_COUNTER (gimple_unroll)
 DEBUG_COUNTER (global_alloc_at_func)
diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index 95c22694368c..3db69ad5733c 100644
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -116,6 +116,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "targhooks.h"
 #include "domwalk.h"
 #include "tree-ssa-math-opts.h"
+#include "dbgcnt.h"
 
 /* This structure represents one basic block that either computes a
    division, or is a common dominator for basic block that compute a
@@ -3366,6 +3367,9 @@ convert_mult_to_fma (gimple *mul_stmt, tree op1, tree op2,
       && !has_single_use (mul_result))
     return false;
 
+  if (!dbg_cnt (form_fma))
+    return false;
+
   /* Make sure that the multiplication statement becomes dead after
      the transformation, thus that all uses are transformed to FMAs.
      This means we assume that an FMA operation has the same cost