pan/bi: Register allocate BLEND dest on Valhall

On Bifrost, BLEND writes to the link register, acting like a function call. On
Valhall, BLEND does not write anything. But the BLEND instruction in our IR is a
pseudo-instruction with Bifrost semantics, expanding to a multi-instruction
sequence on Valhall. So it's not worth special casing Valhall in instruction
selection.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17794>

diff --git a/src/panfrost/bifrost/bifrost_compile.c b/src/panfrost/bifrost/bifrost_compile.c
index cb70f3a..cedd639 100644 (file)
--- a/src/panfrost/bifrost/bifrost_compile.c
+++ b/src/panfrost/bifrost/bifrost_compile.c
@@ -791,9 +791,6 @@ static void
 bi_emit_blend_op(bi_builder *b, bi_index rgba, nir_alu_type T,
                  bi_index rgba2, nir_alu_type T2, unsigned rt)
 {
-        /* On Valhall, BLEND does not encode the return address */
-        bool bifrost = b->shader->arch <= 8;
-
         /* Reads 2 or 4 staging registers to cover the input */
         unsigned size = nir_alu_type_get_type_size(T);
         unsigned size_2 = nir_alu_type_get_type_size(T2);
@@ -819,21 +816,19 @@ bi_emit_blend_op(bi_builder *b, bi_index rgba, nir_alu_type T,
                 /* Blend descriptor comes from the compile inputs */
                 /* Put the result in r0 */
 
-                bi_blend_to(b, bifrost ? bi_temp(b->shader) : bi_null(), rgba,
-                                bi_coverage(b),
-                                bi_imm_u32(blend_desc),
-                                bi_imm_u32(blend_desc >> 32),
-                                bi_null(), regfmt, sr_count, 0);
+                bi_blend_to(b, bi_temp(b->shader), rgba, bi_coverage(b),
+                               bi_imm_u32(blend_desc),
+                               bi_imm_u32(blend_desc >> 32),
+                               bi_null(), regfmt, sr_count, 0);
         } else {
                 /* Blend descriptor comes from the FAU RAM. By convention, the
                  * return address on Bifrost is stored in r48 and will be used
                  * by the blend shader to jump back to the fragment shader */
 
-                bi_blend_to(b, bifrost ? bi_temp(b->shader) : bi_null(), rgba,
-                                bi_coverage(b),
-                                bi_fau(BIR_FAU_BLEND_0 + rt, false),
-                                bi_fau(BIR_FAU_BLEND_0 + rt, true),
-                                rgba2, regfmt, sr_count, sr_count_2);
+                bi_blend_to(b, bi_temp(b->shader), rgba, bi_coverage(b),
+                               bi_fau(BIR_FAU_BLEND_0 + rt, false),
+                               bi_fau(BIR_FAU_BLEND_0 + rt, true),
+                               rgba2, regfmt, sr_count, sr_count_2);
         }
 
         assert(rt < 8);

diff --git a/src/panfrost/bifrost/valhall/test/test-mark-last.cpp b/src/panfrost/bifrost/valhall/test/test-mark-last.cpp
index ae45c5c..f79b9a7 100644 (file)
--- a/src/panfrost/bifrost/valhall/test/test-mark-last.cpp
+++ b/src/panfrost/bifrost/valhall/test/test-mark-last.cpp
@@ -121,18 +121,18 @@ TEST(MarkLast, Half64) {
 
 TEST(MarkLast, RegisterBlendDescriptor) {
    CASE({
-         bi_blend_to(b, bi_null(), R(0), DR(60), DR(4), DR(5), bi_null(),
+         bi_blend_to(b, R(48), R(0), DR(60), DR(4), DR(5), bi_null(),
                      BI_REGISTER_FORMAT_F32, 4, 0);
    });
 
    CASE({
-         bi_blend_to(b, bi_null(), R(0), DR(60), R(4), R(5), bi_null(),
+         bi_blend_to(b, R(48), R(0), DR(60), R(4), R(5), bi_null(),
                      BI_REGISTER_FORMAT_F32, 4, 0);
          bi_fadd_f32_to(b, R(4), DR(4), DR(7));
    });
 
    CASE({
-         bi_blend_to(b, bi_null(), R(0), DR(60), R(4), R(5), bi_null(),
+         bi_blend_to(b, R(48), R(0), DR(60), R(4), R(5), bi_null(),
                      BI_REGISTER_FORMAT_F32, 4, 0);
          bi_fadd_f32_to(b, R(4), DR(5), DR(7));
    });

diff --git a/src/panfrost/bifrost/valhall/va_pack.c b/src/panfrost/bifrost/valhall/va_pack.c
index 949fe38..2b419a7 100644 (file)
--- a/src/panfrost/bifrost/valhall/va_pack.c
+++ b/src/panfrost/bifrost/valhall/va_pack.c
@@ -902,9 +902,6 @@ va_lower_branch_target(bi_context *ctx, bi_block *start, bi_instr *I)
 static void
 va_lower_blend(bi_context *ctx)
 {
-   /* Link register (ABI between fragment and blend shaders) */
-   bi_index lr = bi_register(48);
-
    /* Program counter for *next* instruction */
    bi_index pc = bi_fau(BIR_FAU_PROGRAM_COUNTER, false);
 
@@ -916,10 +913,13 @@ va_lower_blend(bi_context *ctx)
 
       unsigned prolog_length = 2 * 8;
 
+      /* By ABI, r48 is the link register shared with blend shaders */
+      assert(bi_is_equiv(I->dest[0], bi_register(48)));
+
       if (I->flow == VA_FLOW_END)
-         bi_iadd_imm_i32_to(&b, lr, va_zero_lut(), 0);
+         bi_iadd_imm_i32_to(&b, I->dest[0], va_zero_lut(), 0);
       else
-         bi_iadd_imm_i32_to(&b, lr, pc, prolog_length - 8);
+         bi_iadd_imm_i32_to(&b, I->dest[0], pc, prolog_length - 8);
 
       bi_branchzi(&b, va_zero_lut(), I->src[3], BI_CMPF_EQ);