ac/nir: Only clamp shadow reference on radeonsi.

Vulkan CTS does not expect the value to be clamped (at least for D32),
and it makes a differences even though depth is in [0,1], due
to strict inequalities.

I couldn't find anything in the Vulkan spec about this, but the test
seemed to be copied from GL tests and the GL spec only specifies
clamping for fixed point formats. Hence I expect radeonsi to run into
this at some point as well, but given that they still have a usecase
with the Z16->Z32 promotion, I'll leave that for someone else to clean
up.

This at least fixes radv dEQP-VK.texture.shadow.* on VI.

Fixes: 0f9e3251 'ac/nir: clamp shadow texture comparison value on VI'
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/amd/common/ac_nir_to_llvm.c

@@ -4652,14 +4652,14 @@ static void visit_tex(struct ac_nir_context *ctx, nir_tex_instr *instr)
 		LLVMValueRef z = ac_to_float(&ctx->ac,
 		                             llvm_extract_elem(&ctx->ac, comparator, 0));
 
-		/* TC-compatible HTILE promotes Z16 and Z24 to Z32_FLOAT,
+		/* TC-compatible HTILE on radeonsi promotes Z16 and Z24 to Z32_FLOAT,
 		 * so the depth comparison value isn't clamped for Z16 and
 		 * Z24 anymore. Do it manually here.
 		 *
 		 * It's unnecessary if the original texture format was
 		 * Z32_FLOAT, but we don't know that here.
 		 */
-		if (ctx->ac.chip_class == VI)
+		if (ctx->ac.chip_class == VI && ctx->abi->clamp_shadow_reference)
 			z = ac_build_clamp(&ctx->ac, z);
 
 		address[count++] = z;
@@ -6600,6 +6600,7 @@ LLVMModuleRef ac_translate_nir_to_llvm(LLVMTargetMachineRef tm,
 	ctx.abi.emit_outputs = handle_shader_outputs_post;
 	ctx.abi.load_ssbo = radv_load_ssbo;
 	ctx.abi.load_sampler_desc = radv_get_sampler_desc;
+	ctx.abi.clamp_shadow_reference = false;
 
 	if (shader_count >= 2)
 		ac_init_exec_full_mask(&ctx.ac);

src/amd/common/ac_nir_to_llvm.h

@@ -80,6 +80,7 @@ struct ac_nir_compiler_options {
 	struct ac_shader_variant_key key;
 	bool unsafe_math;
 	bool supports_spill;
+	bool clamp_shadow_reference;
 	enum radeon_family family;
 	enum chip_class chip_class;
 };

src/amd/common/ac_shader_abi.h

@@ -88,6 +88,10 @@ struct ac_shader_abi {
 					  LLVMValueRef index,
 					  enum ac_descriptor_type desc_type,
 					  bool image, bool write);
+
+	/* Whether to clamp the shadow reference value to [0,1]on VI. Radeonsi currently
+	 * uses it due to promoting D16 to D32, but radv needs it off. */
+	bool clamp_shadow_reference;
 };
 
 #endif /* AC_SHADER_ABI_H */

src/gallium/drivers/radeonsi/si_shader_nir.c

@@ -498,6 +498,7 @@ bool si_nir_build_llvm(struct si_shader_context *ctx, struct nir_shader *nir)
 
 	ctx->abi.inputs = &ctx->inputs[0];
 	ctx->abi.load_sampler_desc = si_nir_load_sampler_desc;
+	ctx->abi.clamp_shadow_reference = true;
 
 	ctx->num_samplers = util_last_bit(info->samplers_declared);
 	ctx->num_images = util_last_bit(info->images_declared);