aco: fix emitting discard when the program just ends

For fragment shaders that only contain a discard, the exec mask has
to be zero'd and everything discarded.

It seems unnecessary to emit an export here because if the FS has no
exports, the compiler already emits a null export at the end.

Fixes incorrect hair rendering in Detroit: Become Human.

fossil-db (Sienna Cichlid):
Totals from 3 (0.00% of 149839) affected shaders:
CodeSize: 2896 -> 2872 (-0.83%)
Instrs: 556 -> 553 (-0.54%)
Latency: 29266 -> 29214 (-0.18%)
InvThroughput: 3374 -> 3372 (-0.06%)

Cc: 21.1 mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10955>

diff --git a/src/amd/compiler/aco_instruction_selection.cpp b/src/amd/compiler/aco_instruction_selection.cpp
index 8ae43af..9efd01d 100644 (file)
--- a/src/amd/compiler/aco_instruction_selection.cpp
+++ b/src/amd/compiler/aco_instruction_selection.cpp
@@ -5287,11 +5287,8 @@ void visit_discard(isel_context* ctx, nir_intrinsic_instr *instr)
     */
    if (!ctx->cf_info.parent_if.is_divergent) {
       /* program just ends here */
-      ctx->block->kind |= block_kind_uniform;
-      bld.exp(aco_opcode::exp, Operand(v1), Operand(v1), Operand(v1), Operand(v1),
-              0 /* enabled mask */, 9 /* dest */,
-              false /* compressed */, true/* done */, true /* valid mask */);
-      bld.sopp(aco_opcode::s_endpgm);
+      ctx->block->kind |= block_kind_uses_discard_if;
+      bld.pseudo(aco_opcode::p_discard_if, Operand(0xFFFFFFFFu));
       // TODO: it will potentially be followed by a branch which is dead code to sanitize NIR phis
    } else {
       ctx->block->kind |= block_kind_discard;