nir: Don't reassociate add/mul chains containing only constants

The idea here is to reassociate a * (b * c) into (a * c) * b, when
b is a non-constant value, but a and c are constants, allowing them
to be combined.

But nothing was enforcing that 'b' must be non-constant, which meant
that running opt_algebraic in a loop would never terminate if the IR
contained non-folded constant expressions like 256 * 0.5 * 2.  Normally,
we call constant folding in such a loop too, but IMO it's better for
nir_opt_algebraic to be robust and not rely on that.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109581
Fixes: 32e266a9a58 i965: Compile fp64 funcs only if we do not have 64-bit hardware support
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 073e79900cb7db16880983186af1d34c8d6839e9..ba27d702b5db63abcc274632f4992ac5850e2f25 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -636,11 +636,11 @@ optimizations = [
    # Reassociate constants in add/mul chains so they can be folded together.
    # For now, we mostly only handle cases where the constants are separated by
    # a single non-constant.  We could do better eventually.
-   (('~fmul', '#a', ('fmul', b, '#c')), ('fmul', ('fmul', a, c), b)),
-   (('imul', '#a', ('imul', b, '#c')), ('imul', ('imul', a, c), b)),
-   (('~fadd', '#a',          ('fadd', b, '#c')),  ('fadd', ('fadd', a,          c),           b)),
-   (('~fadd', '#a', ('fneg', ('fadd', b, '#c'))), ('fadd', ('fadd', a, ('fneg', c)), ('fneg', b))),
-   (('iadd', '#a', ('iadd', b, '#c')), ('iadd', ('iadd', a, c), b)),
+   (('~fmul', '#a', ('fmul', 'b(is_not_const)', '#c')), ('fmul', ('fmul', a, c), b)),
+   (('imul', '#a', ('imul', 'b(is_not_const)', '#c')), ('imul', ('imul', a, c), b)),
+   (('~fadd', '#a',          ('fadd', 'b(is_not_const)', '#c')),  ('fadd', ('fadd', a,          c),           b)),
+   (('~fadd', '#a', ('fneg', ('fadd', 'b(is_not_const)', '#c'))), ('fadd', ('fadd', a, ('fneg', c)), ('fneg', b))),
+   (('iadd', '#a', ('iadd', 'b(is_not_const)', '#c')), ('iadd', ('iadd', a, c), b)),
 
    # By definition...
    (('bcsel', ('ige', ('find_lsb', a), 0), ('find_lsb', a), -1), ('find_lsb', a)),