Re: [Mesa-dev] [Mesa-stable] [PATCH] radeonsi: add a workaround for bitfield_extract when count is 0

[Samuel Pitoiset]

On 9/25/18 6:46 AM, Timothy Arceri wrote:
On 25/9/18 10:35 am, Marek Olšák wrote:
Do you know what's broken in LLVM? Or is it a problem with the ISA?

I haven't actually dug any further. Adding Samuel to see if he remembers 
more.

However according to the original bug report this is a regression when 
going from LLVM 6 to LLVM 7. I see the issue on both polaris and vega.

I didn't investigate either, it was just simpler to add a workaround in 
mesa than fixing LLVM.



Marek

On Fri, Sep 21, 2018 at 10:38 PM, Timothy Arceri 
<tarc...@itsqueeze.com> wrote:
This ports the fix from 3d41757788ac. Both LLVM 7 & 8 continue
to have this problem.

It fixes rendering issues in some menu and loading screens of
Civ VI which can be seen in the trace from bug 104602.

Note: This does not fix the black triangles on Vega for bug
104602.

Cc: mesa-sta...@lists.freedesktop.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104602
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107276
---
  .../drivers/radeonsi/si_shader_tgsi_alu.c     | 41 ++++++++++++++-----
  1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c 
b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
index f54d025aec0..814362bc963 100644
--- a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
+++ b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
@@ -494,18 +494,37 @@ static void emit_bfe(const struct 
lp_build_tgsi_action *action,
                      struct lp_build_emit_data *emit_data)
  {
         struct si_shader_context *ctx = si_shader_context(bld_base);
-       LLVMValueRef bfe_sm5;
-       LLVMValueRef cond;
-
-       bfe_sm5 = ac_build_bfe(&ctx->ac, emit_data->args[0],
-                              emit_data->args[1], emit_data->args[2],
-                              emit_data->info->opcode == 
TGSI_OPCODE_IBFE);

-       /* Correct for GLSL semantics. */
-       cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, 
emit_data->args[2],
-                            LLVMConstInt(ctx->i32, 32, 0), "");
-       emit_data->output[emit_data->chan] =
-               LLVMBuildSelect(ctx->ac.builder, cond, 
emit_data->args[0], bfe_sm5, "");
+       if (HAVE_LLVM < 0x0700) {
+               LLVMValueRef bfe_sm5 =
+                       ac_build_bfe(&ctx->ac, emit_data->args[0],
+                                    emit_data->args[1], 
emit_data->args[2],
+                                    emit_data->info->opcode == 
TGSI_OPCODE_IBFE);
+
+               /* Correct for GLSL semantics. */
+               LLVMValueRef cond = LLVMBuildICmp(ctx->ac.builder, 
LLVMIntUGE, emit_data->args[2],
+                                                 
LLVMConstInt(ctx->i32, 32, 0), "");
+               emit_data->output[emit_data->chan] =
+                       LLVMBuildSelect(ctx->ac.builder, cond, 
emit_data->args[0], bfe_sm5, "");
+       } else {
+               /* FIXME: LLVM 7 returns incorrect result when count 
is 0.
+                * https://bugs.freedesktop.org/show_bug.cgi?id=107276
+                */
+               LLVMValueRef zero = ctx->i32_0;
+               LLVMValueRef bfe_sm5 =
+                       ac_build_bfe(&ctx->ac, emit_data->args[0],
+                                    emit_data->args[1], 
emit_data->args[2],
+                                    emit_data->info->opcode == 
TGSI_OPCODE_IBFE);
+
+               /* Correct for GLSL semantics. */
+               LLVMValueRef cond = LLVMBuildICmp(ctx->ac.builder, 
LLVMIntUGE, emit_data->args[2],
+                                                 
LLVMConstInt(ctx->i32, 32, 0), "");
+               LLVMValueRef cond2 = LLVMBuildICmp(ctx->ac.builder, 
LLVMIntEQ, emit_data->args[2],
+                                                  zero, "");
+               bfe_sm5 = LLVMBuildSelect(ctx->ac.builder, cond, 
emit_data->args[0], bfe_sm5, "");
+               emit_data->output[emit_data->chan] =
+                       LLVMBuildSelect(ctx->ac.builder, cond2, zero, 
bfe_sm5, "");
+       }
  }

  /* this is ffs in C */
--
2.17.1

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