Re: [Mesa-dev] [PATCH] gallivm: fix [IU]MUL_HI regression harder

[Nicolai Hähnle]

On 09.11.2016 16:10, Roland Scheidegger wrote:
Am 09.11.2016 um 14:55 schrieb Nicolai Hähnle:
On 09.11.2016 14:46, Roland Scheidegger wrote:
Reviewed-by: Roland Scheidegger <srol...@vmware.com>
I'm curious though, is for radeonsi zext not equivalent to interleaving
the low 32bits of each number with zeros (and hence doing the a
uninterleave doesn't give you back the low respectively high bits)?

radeonsi ends up calling lp_build_mul_32_lohi once for each component of
the vector, with no vector types involved at all, it's all plain i32 and
i64. This is better for the CodeGen backend in LLVM.

The code was previously returning a <1 x i32> for each component, and
that caused the later stages of opcode handling to get confused about
what to do with the result.
So casting the result to a scalar would have fixed this too? This is
actually sort of a deficiency of lp_build_uninterleave1 - the
lp_build_xx code usually is built to avoid 1xn vector types and use
scalars in that case, but not quite everywhere.

I think casting to scalars could work as well. If that would be 
preferable for llvmpipe, I can give it shot.

Nicolai


Roland



Cheers,
Nicolai


Roland

Am 09.11.2016 um 12:46 schrieb Nicolai Hähnle:
From: Nicolai Hähnle <nicolai.haeh...@amd.com>

The fix in commit 88f791db75e9f065bac8134e0937e1b76600aa36 was
insufficient
for radeonsi because the vector case was not handled properly. It seems
piglit only covers the scalar case, unfortunately.

Fixes GL45-CTS.shader_bitfield_operation.[iu]mulExtended.*
---
 src/gallium/auxiliary/gallivm/lp_bld_arit.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
index 43ad238..5553cb1 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
@@ -1230,42 +1230,46 @@ lp_build_mul_32_lohi_cpu(struct
lp_build_context *bld,
  * Emits generic code.
  */
 LLVMValueRef
 lp_build_mul_32_lohi(struct lp_build_context *bld,
                      LLVMValueRef a,
                      LLVMValueRef b,
                      LLVMValueRef *res_hi)
 {
    struct gallivm_state *gallivm = bld->gallivm;
    LLVMBuilderRef builder = gallivm->builder;
-   LLVMValueRef tmp;
+   LLVMValueRef tmp, shift, res_lo;
    struct lp_type type_tmp;
-   LLVMTypeRef wide_type, cast_type;
+   LLVMTypeRef wide_type, narrow_type;

    type_tmp = bld->type;
+   narrow_type = lp_build_vec_type(gallivm, type_tmp);
    type_tmp.width *= 2;
    wide_type = lp_build_vec_type(gallivm, type_tmp);
-   type_tmp = bld->type;
-   type_tmp.length *= 2;
-   cast_type = lp_build_vec_type(gallivm, type_tmp);
+   shift = lp_build_const_vec(gallivm, type_tmp, 32);

    if (bld->type.sign) {
       a = LLVMBuildSExt(builder, a, wide_type, "");
       b = LLVMBuildSExt(builder, b, wide_type, "");
    } else {
       a = LLVMBuildZExt(builder, a, wide_type, "");
       b = LLVMBuildZExt(builder, b, wide_type, "");
    }
    tmp = LLVMBuildMul(builder, a, b, "");
-   tmp = LLVMBuildBitCast(builder, tmp, cast_type, "");
-   *res_hi = lp_build_uninterleave1(gallivm, bld->type.length * 2,
tmp, 1);
-   return lp_build_uninterleave1(gallivm, bld->type.length * 2, tmp,
0);
+
+   res_lo = LLVMBuildTrunc(builder, tmp, narrow_type, "");
+
+   /* Since we truncate anyway, LShr and AShr are equivalent. */
+   tmp = LLVMBuildLShr(builder, tmp, shift, "");
+   *res_hi = LLVMBuildTrunc(builder, tmp, narrow_type, "");
+
+   return res_lo;
 }


 /* a * b + c */
 LLVMValueRef
 lp_build_mad(struct lp_build_context *bld,
              LLVMValueRef a,
              LLVMValueRef b,
              LLVMValueRef c)
 {



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