nir+r600: add option to avoid contracting fabs into ffma

On r600 ternary operations can't use the fabs source modifier, so
converting "fadd(fabs(fmul(a, b), c)" to  "ffma(fabs(a), fabs(b), c)"
adds one more instruction in the backend, hence avoid this.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37440>

src/compiler/nir/nir_opt_algebraic.py

@@ -3650,6 +3650,7 @@ for sz, mulz in itertools.product([16, 32, 64], [False, True]):
 
     fadd = 'fadd@{}(contract)'.format(sz)
     option = 'options->fuse_ffma{}'.format(sz)
+    option_with_abs = 'options->fuse_ffma{}  && !options->avoid_ternary_with_fabs'.format(sz)
 
     late_optimizations.extend([
         ((fadd, (fmul, a, b), c), (ffma, a, b, c), option),
@@ -3658,10 +3659,10 @@ for sz, mulz in itertools.product([16, 32, 64], [False, True]):
          (ffma, ('fneg', a), b, c), option),
 
         ((fadd, ('fabs(is_only_used_by_fadd)', (fmul, a, b)), c),
-         (ffma, ('fabs', a), ('fabs', b), c), option),
+         (ffma, ('fabs', a), ('fabs', b), c), option_with_abs),
 
         ((fadd, ('fneg(is_only_used_by_fadd)', ('fabs', (fmul, a, b))), c),
-         (ffma, ('fneg', ('fabs', a)), ('fabs', b), c), option),
+         (ffma, ('fneg', ('fabs', a)), ('fabs', b), c), option_with_abs),
     ])
 
 late_optimizations.extend([

src/compiler/nir/nir_shader_compiler_options.h

@@ -665,6 +665,11 @@ typedef struct nir_shader_compiler_options {
     */
    bool avoid_ternary_with_two_constants;
 
+   /* Avoid using fabs on sources to ternary operations
+    * r600 can't use source modifiers for these
+    */
+   bool avoid_ternary_with_fabs;
+
    /** Whether 8-bit ALU is supported. */
    bool support_8bit_alu;
 

src/gallium/drivers/r600/r600_pipe_common.c

@@ -1166,6 +1166,7 @@ bool r600_common_screen_init(struct r600_common_screen *rscreen,
 		.vectorize_tess_levels = 1,
 		.io_options = nir_io_mediump_is_32bit,
 		.vertex_id_zero_based = rscreen->info.gfx_level >= EVERGREEN,
+		.avoid_ternary_with_fabs = 1,
 	};
 
 	rscreen->nir_options = nir_options;