[Mesa-dev] [PATCH] gallivm: Fix lp_build_float_to_half.
Jose Fonseca
jfonseca at vmware.com
Thu Nov 29 07:50:48 PST 2012
----- Original Message -----
> On 11/29/2012 08:32 AM, jfonseca at vmware.com wrote:
> > From: José Fonseca<jfonseca at vmware.com>
> >
> > The current implementation was close by not fully correct: several
> > operations that should be done in floating point were being done in
> > integer.
> >
> > Fixes piglit fbo-clear-formats GL_ARB_texture_float
> > ---
> > src/gallium/auxiliary/gallivm/lp_bld_conv.c | 103
> > +++++++++++++++++++--------
> > 1 file changed, 73 insertions(+), 30 deletions(-)
> >
> > diff --git a/src/gallium/auxiliary/gallivm/lp_bld_conv.c
> > b/src/gallium/auxiliary/gallivm/lp_bld_conv.c
> > index cd18b0c..a48b053 100644
> > --- a/src/gallium/auxiliary/gallivm/lp_bld_conv.c
> > +++ b/src/gallium/auxiliary/gallivm/lp_bld_conv.c
> > @@ -63,15 +63,18 @@
> >
> > #include "util/u_debug.h"
> > #include "util/u_math.h"
> > +#include "util/u_half.h"
> > #include "util/u_cpu_detect.h"
> >
> > #include "lp_bld_type.h"
> > #include "lp_bld_const.h"
> > #include "lp_bld_arit.h"
> > +#include "lp_bld_bitarit.h"
> > #include "lp_bld_pack.h"
> > #include "lp_bld_conv.h"
> > #include "lp_bld_logic.h"
> > #include "lp_bld_intr.h"
> > +#include "lp_bld_printf.h"
> >
> >
> >
> > @@ -220,64 +223,104 @@ lp_build_half_to_float(struct gallivm_state
> > *gallivm,
> > *
> > * ref
> > http://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
> > * ref https://gist.github.com/2156668
> > + *
> > + * XXX: This is approximation. It is is faster certain NaNs are
> > converted to
> > + * infinity, and rounding is not correct.
>
> I can't quite parse that comment.
Oops. Will correct.
> > */
> > LLVMValueRef
> > lp_build_float_to_half(struct gallivm_state *gallivm,
> > LLVMValueRef src)
> > {
> > - struct lp_type i32_type = lp_type_int_vec(32, 32 *
> > LLVMGetVectorSize(LLVMTypeOf(src)));
> > -
> > LLVMBuilderRef builder = gallivm->builder;
> > - LLVMTypeRef int_vec_type = lp_build_vec_type(gallivm,
> > i32_type);
> > -
> > - struct lp_build_context bld;
> > -
> > + LLVMTypeRef f32_vec_type = LLVMTypeOf(src);
> > + unsigned length = LLVMGetTypeKind(f32_vec_type) ==
> > LLVMVectorTypeKind
> > + ? LLVMGetVectorSize(f32_vec_type) : 1;
> > + struct lp_type f32_type = lp_type_float_vec(32, 32 * length);
> > + struct lp_type u32_type = lp_type_uint_vec(32, 32 * length);
> > + struct lp_type i16_type = lp_type_int_vec(16, 16 * length);
> > + LLVMTypeRef u32_vec_type = lp_build_vec_type(gallivm,
> > u32_type);
> > + LLVMTypeRef i16_vec_type = lp_build_vec_type(gallivm,
> > i16_type);
> > + struct lp_build_context f32_bld;
> > + struct lp_build_context u32_bld;
> > LLVMValueRef result;
> >
> > - lp_build_context_init(&bld, gallivm, i32_type);
> > + lp_build_context_init(&f32_bld, gallivm, f32_type);
> > + lp_build_context_init(&u32_bld, gallivm, u32_type);
> >
> > - /* Extra scope because lp_build_min needs a build context, le
> > sigh */
> > {
> > /* Constants */
> > - LLVMValueRef i32_13 = lp_build_const_int_vec(gallivm,
> > i32_type, 13);
> > - LLVMValueRef i32_16 = lp_build_const_int_vec(gallivm,
> > i32_type, 16);
> > - LLVMValueRef i32_mask_fabs = lp_build_const_int_vec(gallivm,
> > i32_type, 0x7fffffff);
> > - LLVMValueRef i32_f32infty = lp_build_const_int_vec(gallivm,
> > i32_type, 0xff<< 23);
> > - LLVMValueRef i32_expinf = lp_build_const_int_vec(gallivm,
> > i32_type, 0xe0<< 23);
> > - LLVMValueRef i32_f16max = lp_build_const_int_vec(gallivm,
> > i32_type, 0x8f<< 23);
> > - LLVMValueRef i32_magic = lp_build_const_int_vec(gallivm,
> > i32_type, 0x0f<< 23);
> > + LLVMValueRef u32_f32inf = lp_build_const_int_vec(gallivm,
> > u32_type, 0xff<< 23);
> > + LLVMValueRef u32_expinf = lp_build_const_int_vec(gallivm,
> > u32_type, 0xe0<< 23);
> > + LLVMValueRef f32_f16max = lp_build_const_vec(gallivm,
> > f32_type, 65536.0); // 0x8f<< 23
> > + LLVMValueRef f32_magic = lp_build_const_vec(gallivm,
> > f32_type, 1.92592994e-34); // 0x0f<< 23
> >
> > /* Cast from float32 to int32 */
> > - LLVMValueRef f = LLVMBuildBitCast(builder, src,
> > int_vec_type, "");
> > + LLVMValueRef f = LLVMBuildBitCast(builder, src,
> > u32_vec_type, "");
> >
> > /* Remove sign */
> > - LLVMValueRef fabs = LLVMBuildAnd(builder,
> > i32_mask_fabs, f, "");
> > + LLVMValueRef srcabs = lp_build_abs(&f32_bld, src);
> > + LLVMValueRef fabs = LLVMBuildBitCast(builder,
> > srcabs, u32_vec_type, "");
> >
> > /* Magic conversion */
> > - LLVMValueRef clamped = lp_build_min(&bld, i32_f16max,
> > fabs);
> > - LLVMValueRef scaled = LLVMBuildMul(builder, clamped,
> > i32_magic, "");
> > -
> > + LLVMValueRef clamped = lp_build_min(&f32_bld,
> > f32_f16max, srcabs);
> > + LLVMValueRef scaled = LLVMBuildBitCast(builder,
> > +
> > LLVMBuildFMul(builder,
> > +
> > clamped,
> > +
> > f32_magic,
> > +
> > ""),
> > + u32_vec_type,
> > + "");
> > /* Make sure Inf/NaN and unormalised survive */
> > - LLVMValueRef infnancase = LLVMBuildXor(builder,
> > i32_expinf, fabs, "");
> > - LLVMValueRef b_notnormal = lp_build_compare(gallivm,
> > i32_type, PIPE_FUNC_GREATER, fabs, i32_f32infty);
> > + LLVMValueRef infnancase = LLVMBuildXor(builder,
> > u32_expinf, fabs, "");
> > + LLVMValueRef b_notnormal = lp_build_compare(gallivm,
> > f32_type, PIPE_FUNC_GEQUAL,
> > + srcabs,
> > +
> > LLVMBuildBitCast(builder,
> > u32_f32inf, f32_vec_type, ""));
> >
> > /* Merge normal / unnormal case */
> > - LLVMValueRef merge1 = LLVMBuildAnd(builder,
> > infnancase, b_notnormal, "");
> > - LLVMValueRef merge2 = LLVMBuildNot(builder,
> > LLVMBuildAnd(builder, b_notnormal, scaled, ""), "");
> > - LLVMValueRef merged = LLVMBuildOr(builder, merge1,
> > merge2, "");
> > - LLVMValueRef shifted = LLVMBuildLShr(builder, merged,
> > i32_13, "");
> > + LLVMValueRef merged = lp_build_select(&u32_bld,
> > b_notnormal, infnancase, scaled);
> > + LLVMValueRef shifted = lp_build_shr_imm(&u32_bld,
> > merged, 13);
> >
> > /* Sign bit */
> > LLVMValueRef justsign = LLVMBuildXor(builder, f, fabs,
> > "");
> > - LLVMValueRef signshifted = LLVMBuildLShr(builder,
> > justsign, i32_16, "");
> > + LLVMValueRef signshifted = lp_build_shr_imm(&u32_bld,
> > justsign, 16);
> >
> > /* Combine result */
> > result = LLVMBuildOr(builder, shifted,
> > signshifted, "");
> > }
> >
> > - /* Truncate from 32 bit to 16 bit */
> > - i32_type.width = 16;
> > - return LLVMBuildTrunc(builder, result,
> > lp_build_vec_type(gallivm, i32_type), "");
> > + result = LLVMBuildTrunc(builder, result, i16_vec_type, "");
> > +
>
> The following if (0) block is just debug code, right?
Yes.
> It's a little
> suspect because it manipulates the 'result' return value. Maybe add
> a
> comment about what's going on.
I'm sure we'll need to revisit this code, due to the liberties it takes converting, which is why I left the debug code here. I'll add a comment to this effect.
>
> > + if (0) {
> > + LLVMTypeRef i32t = LLVMInt32TypeInContext(gallivm->context);
> > + LLVMTypeRef i16t = LLVMInt16TypeInContext(gallivm->context);
> > + LLVMTypeRef f32t = LLVMFloatTypeInContext(gallivm->context);
> > + unsigned i;
> > +
> > + LLVMTypeRef func_type = LLVMFunctionType(i16t,&f32t, 1, 0);
> > + LLVMValueRef func = lp_build_const_int_pointer(gallivm,
> > func_to_pointer((func_pointer)util_float_to_half));
> > + func = LLVMBuildBitCast(builder, func,
> > LLVMPointerType(func_type, 0), "util_float_to_half");
> > +
> > + lp_build_print_value(gallivm, "src = ", src);
> > + lp_build_print_value(gallivm, "util = ", result);
> > + lp_build_print_value(gallivm, "llvm = ", result);
> > +
> > + result = LLVMGetUndef(LLVMVectorType(i16t, length));
> > + for (i = 0; i< length; ++i) {
> > + LLVMValueRef index = LLVMConstInt(i32t, i, 0);
> > + LLVMValueRef f32 = LLVMBuildExtractElement(builder, src,
> > index, "");
> > +#if 0
> > + /* XXX: not really supported by backends */
> > + LLVMValueRef f16 = lp_build_intrinsic_unary(builder,
> > "llvm.convert.to.fp16", i16t, f32);
> > +#else
> > + LLVMValueRef f16 = LLVMBuildCall(builder, func,&f32, 1,
> > "");
> > +#endif
> > + result = LLVMBuildInsertElement(builder, result, f16,
> > index, "");
> > + }
> > +
> > + lp_build_printf(gallivm, "\n");
> > + }
> > +
> > + return result;
> > }
> >
> >
>
> I didn't study the code in detail (it's pretty dense), but it looks
> OK
> on the surface. Roland?
>
> Reviewed-by: Brian Paul <brianp at vmware.com>
Thanks.
Jose
More information about the mesa-dev
mailing list