intel/fs: Fix D to W conversion in opt_combine_constants

Found by GCC warning:

src/intel/compiler/brw_fs_combine_constants.cpp: In function ‘bool needs_negate(const fs_reg*, const imm*)’:
src/intel/compiler/brw_fs_combine_constants.cpp:306:34: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
       return ((reg->d & 0xffffu) < 0) != (imm->w < 0);
               ~~~~~~~~~~~~~~~~~~~^~~

The result of the bit-and is a 32-bit value with the top bits all zero.
This will never be < 0.  Instead of masking off the bits, just cast to
int16_t and let the compiler handle the actual conversion.

Fixes: e64be391dd0 ("intel/compiler: generalize the combine constants pass")
Cc: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

diff --git a/src/intel/compiler/brw_fs_combine_constants.cpp b/src/intel/compiler/brw_fs_combine_constants.cpp
index db7b14a..8d16be4 100644 (file)
--- a/src/intel/compiler/brw_fs_combine_constants.cpp
+++ b/src/intel/compiler/brw_fs_combine_constants.cpp
@@ -303,7 +303,7 @@ needs_negate(const struct fs_reg *reg, const struct imm *imm)
    case BRW_REGISTER_TYPE_HF:
       return (reg->d & 0x8000u) != (imm->w & 0x8000u);
    case BRW_REGISTER_TYPE_W:
-      return ((reg->d & 0xffffu) < 0) != (imm->w < 0);
+      return ((int16_t)reg->d < 0) != (imm->w < 0);
    case BRW_REGISTER_TYPE_UQ:
    case BRW_REGISTER_TYPE_UD:
    case BRW_REGISTER_TYPE_UW: