[Mesa-stable] [PATCH] ac/nir: mark some texture intrinsics as convergent

[Rhys Perry]

Otherwise LLVM can sink them and their texture coordinate calculations
into divergent branches.

Cc: <mesa-stable at lists.freedesktop.org>
Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
---
 src/amd/common/ac_nir_to_llvm.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
index 265e3b636c4..d2dc617de36 100644
--- a/src/amd/common/ac_nir_to_llvm.c
+++ b/src/amd/common/ac_nir_to_llvm.c
@@ -1316,6 +1316,30 @@ static nir_deref_instr *get_tex_texture_deref(const nir_tex_instr *instr)
 	return texture_deref_instr;
 }
 
+static bool has_implicit_derivatives(const nir_tex_instr *instr)
+{
+	switch (instr->op) {
+	case nir_texop_txs:
+	case nir_texop_query_levels:
+	case nir_texop_texture_samples:
+	case nir_texop_samples_identical:
+		return false;
+	default:
+		break;
+	}
+	for (unsigned i = 0; i < instr->num_srcs; i++) {
+		switch (instr->src[i].src_type) {
+		case nir_tex_src_lod:
+		case nir_tex_src_ddx:
+		case nir_tex_src_ddy:
+			return false;
+		default:
+			break;
+		}
+	}
+	return true;
+}
+
 static LLVMValueRef build_tex_intrinsic(struct ac_nir_context *ctx,
 					const nir_tex_instr *instr,
 					struct ac_image_args *args)
@@ -1394,6 +1418,11 @@ static LLVMValueRef build_tex_intrinsic(struct ac_nir_context *ctx,
 	}
 
 	args->attributes = AC_FUNC_ATTR_READNONE;
+	/* Prevent texture instructions with implicit derivatives from being
+	 * sinked into branches. */
+	if (has_implicit_derivatives(instr))
+		args->attributes |= AC_FUNC_ATTR_CONVERGENT;
+
 	return ac_build_image_opcode(&ctx->ac, args);
 }
 
-- 
2.21.0