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: <[email protected]>
Reviewed-by: Jason Ekstrand <[email protected]>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index a01b01048c8..beeac84e43d 100644
--- 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));