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| <h4 class="subsection">3.17.2 Adapteva Epiphany Options</h4> |
| |
| <p>These ‘<samp><span class="samp">-m</span></samp>’ options are defined for Adapteva Epiphany: |
| |
| <dl> |
| <dt><code>-mhalf-reg-file</code><dd><a name="index-mhalf_002dreg_002dfile-1096"></a>Don't allocate any register in the range <code>r32</code><small class="dots">...</small><code>r63</code>. |
| That allows code to run on hardware variants that lack these registers. |
| |
| <br><dt><code>-mprefer-short-insn-regs</code><dd><a name="index-mprefer_002dshort_002dinsn_002dregs-1097"></a>Preferrentially allocate registers that allow short instruction generation. |
| This can result in increased instruction count, so this may either reduce or |
| increase overall code size. |
| |
| <br><dt><code>-mbranch-cost=</code><var>num</var><dd><a name="index-mbranch_002dcost-1098"></a>Set the cost of branches to roughly <var>num</var> “simple” instructions. |
| This cost is only a heuristic and is not guaranteed to produce |
| consistent results across releases. |
| |
| <br><dt><code>-mcmove</code><dd><a name="index-mcmove-1099"></a>Enable the generation of conditional moves. |
| |
| <br><dt><code>-mnops=</code><var>num</var><dd><a name="index-mnops-1100"></a>Emit <var>num</var> NOPs before every other generated instruction. |
| |
| <br><dt><code>-mno-soft-cmpsf</code><dd><a name="index-mno_002dsoft_002dcmpsf-1101"></a>For single-precision floating-point comparisons, emit an <code>fsub</code> instruction |
| and test the flags. This is faster than a software comparison, but can |
| get incorrect results in the presence of NaNs, or when two different small |
| numbers are compared such that their difference is calculated as zero. |
| The default is <samp><span class="option">-msoft-cmpsf</span></samp>, which uses slower, but IEEE-compliant, |
| software comparisons. |
| |
| <br><dt><code>-mstack-offset=</code><var>num</var><dd><a name="index-mstack_002doffset-1102"></a>Set the offset between the top of the stack and the stack pointer. |
| E.g., a value of 8 means that the eight bytes in the range <code>sp+0...sp+7</code> |
| can be used by leaf functions without stack allocation. |
| Values other than ‘<samp><span class="samp">8</span></samp>’ or ‘<samp><span class="samp">16</span></samp>’ are untested and unlikely to work. |
| Note also that this option changes the ABI; compiling a program with a |
| different stack offset than the libraries have been compiled with |
| generally does not work. |
| This option can be useful if you want to evaluate if a different stack |
| offset would give you better code, but to actually use a different stack |
| offset to build working programs, it is recommended to configure the |
| toolchain with the appropriate <samp><span class="option">--with-stack-offset=</span><var>num</var></samp> option. |
| |
| <br><dt><code>-mno-round-nearest</code><dd><a name="index-mno_002dround_002dnearest-1103"></a>Make the scheduler assume that the rounding mode has been set to |
| truncating. The default is <samp><span class="option">-mround-nearest</span></samp>. |
| |
| <br><dt><code>-mlong-calls</code><dd><a name="index-mlong_002dcalls-1104"></a>If not otherwise specified by an attribute, assume all calls might be beyond |
| the offset range of the <code>b</code> / <code>bl</code> instructions, and therefore load the |
| function address into a register before performing a (otherwise direct) call. |
| This is the default. |
| |
| <br><dt><code>-mshort-calls</code><dd><a name="index-short_002dcalls-1105"></a>If not otherwise specified by an attribute, assume all direct calls are |
| in the range of the <code>b</code> / <code>bl</code> instructions, so use these instructions |
| for direct calls. The default is <samp><span class="option">-mlong-calls</span></samp>. |
| |
| <br><dt><code>-msmall16</code><dd><a name="index-msmall16-1106"></a>Assume addresses can be loaded as 16-bit unsigned values. This does not |
| apply to function addresses for which <samp><span class="option">-mlong-calls</span></samp> semantics |
| are in effect. |
| |
| <br><dt><code>-mfp-mode=</code><var>mode</var><dd><a name="index-mfp_002dmode-1107"></a>Set the prevailing mode of the floating-point unit. |
| This determines the floating-point mode that is provided and expected |
| at function call and return time. Making this mode match the mode you |
| predominantly need at function start can make your programs smaller and |
| faster by avoiding unnecessary mode switches. |
| |
| <p><var>mode</var> can be set to one the following values: |
| |
| <dl> |
| <dt>‘<samp><span class="samp">caller</span></samp>’<dd>Any mode at function entry is valid, and retained or restored when |
| the function returns, and when it calls other functions. |
| This mode is useful for compiling libraries or other compilation units |
| you might want to incorporate into different programs with different |
| prevailing FPU modes, and the convenience of being able to use a single |
| object file outweighs the size and speed overhead for any extra |
| mode switching that might be needed, compared with what would be needed |
| with a more specific choice of prevailing FPU mode. |
| |
| <br><dt>‘<samp><span class="samp">truncate</span></samp>’<dd>This is the mode used for floating-point calculations with |
| truncating (i.e. round towards zero) rounding mode. That includes |
| conversion from floating point to integer. |
| |
| <br><dt>‘<samp><span class="samp">round-nearest</span></samp>’<dd>This is the mode used for floating-point calculations with |
| round-to-nearest-or-even rounding mode. |
| |
| <br><dt>‘<samp><span class="samp">int</span></samp>’<dd>This is the mode used to perform integer calculations in the FPU, e.g. |
| integer multiply, or integer multiply-and-accumulate. |
| </dl> |
| |
| <p>The default is <samp><span class="option">-mfp-mode=caller</span></samp> |
| |
| <br><dt><code>-mnosplit-lohi</code><dt><code>-mno-postinc</code><dt><code>-mno-postmodify</code><dd><a name="index-mnosplit_002dlohi-1108"></a><a name="index-mno_002dpostinc-1109"></a><a name="index-mno_002dpostmodify-1110"></a>Code generation tweaks that disable, respectively, splitting of 32-bit |
| loads, generation of post-increment addresses, and generation of |
| post-modify addresses. The defaults are <samp><span class="option">msplit-lohi</span></samp>, |
| <samp><span class="option">-mpost-inc</span></samp>, and <samp><span class="option">-mpost-modify</span></samp>. |
| |
| <br><dt><code>-mnovect-double</code><dd><a name="index-mno_002dvect_002ddouble-1111"></a>Change the preferred SIMD mode to SImode. The default is |
| <samp><span class="option">-mvect-double</span></samp>, which uses DImode as preferred SIMD mode. |
| |
| <br><dt><code>-max-vect-align=</code><var>num</var><dd><a name="index-max_002dvect_002dalign-1112"></a>The maximum alignment for SIMD vector mode types. |
| <var>num</var> may be 4 or 8. The default is 8. |
| Note that this is an ABI change, even though many library function |
| interfaces are unaffected if they don't use SIMD vector modes |
| in places that affect size and/or alignment of relevant types. |
| |
| <br><dt><code>-msplit-vecmove-early</code><dd><a name="index-msplit_002dvecmove_002dearly-1113"></a>Split vector moves into single word moves before reload. In theory this |
| can give better register allocation, but so far the reverse seems to be |
| generally the case. |
| |
| <br><dt><code>-m1reg-</code><var>reg</var><dd><a name="index-m1reg_002d-1114"></a>Specify a register to hold the constant −1, which makes loading small negative |
| constants and certain bitmasks faster. |
| Allowable values for <var>reg</var> are ‘<samp><span class="samp">r43</span></samp>’ and ‘<samp><span class="samp">r63</span></samp>’, |
| which specify use of that register as a fixed register, |
| and ‘<samp><span class="samp">none</span></samp>’, which means that no register is used for this |
| purpose. The default is <samp><span class="option">-m1reg-none</span></samp>. |
| |
| </dl> |
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