intel/fs: Fix lowering of dword multiplication by 16-bit constant

Existing code was ignoring whether the type of the immediate source
was signed or not.  If the source was signed, it would ignore small
negative values but it also would wrongly accept values between
INT16_MAX and UINT16_MAX, causing the atual value to later be
reinterpreted as a negative number (under 16-bits).

Fixes tests/shaders/glsl-mul-const.shader_test in Piglit for platforms
that don't support MUL with 32x32 types, including ICL and TGL.

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2186
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index a01b01048c8dcbb201d9206b5b24da1bba0e4a9a..beeac84e43d3ef4f29ea4478cbb883838177e562 100644 (file)
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -3908,7 +3908,10 @@ fs_visitor::lower_mul_dword_inst(fs_inst *inst, bblock_t *block)
 {
    const fs_builder ibld(this, block, inst);
 
-   if (inst->src[1].file == IMM && inst->src[1].ud < (1 << 16)) {
+   const bool ud = (inst->src[1].type == BRW_REGISTER_TYPE_UD);
+   if (inst->src[1].file == IMM &&
+       (( ud && inst->src[1].ud <= UINT16_MAX) ||
+        (!ud && inst->src[1].d <= INT16_MAX && inst->src[1].d >= INT16_MIN))) {
       /* The MUL instruction isn't commutative. On Gen <= 6, only the low
        * 16-bits of src0 are read, and on Gen >= 7 only the low 16-bits of
        * src1 are used.
@@ -3921,7 +3924,6 @@ fs_visitor::lower_mul_dword_inst(fs_inst *inst, bblock_t *block)
          ibld.MOV(imm, inst->src[1]);
          ibld.MUL(inst->dst, imm, inst->src[0]);
       } else {
-         const bool ud = (inst->src[1].type == BRW_REGISTER_TYPE_UD);
          ibld.MUL(inst->dst, inst->src[0],
                   ud ? brw_imm_uw(inst->src[1].ud)
                      : brw_imm_w(inst->src[1].d));