pan/bi: Use FCLAMP pseudo op for clamp prop

Map nir_op_fsat/etc to FCLAMP pseudo ops, instead of FADD. There are
significantly fewer knobs on FCLAMP, meaning significantly fewer things
to get wrong.

This fixes two(!) classes of bugs:

* Swizzles (failing to lower/compose swizzles on clamps)
* Numerical bugs (incorrectly treating +0.0 as an additive identity)

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12205>

src/panfrost/bifrost/ISA.xml

@@ -8313,4 +8313,24 @@
     </mod>
   </ins>
 
+  <ins name="*FCLAMP.f32" pseudo="true">
+    <src start="0" mask="0xfb"/>
+    <mod name="clamp" start="15" size="2">
+      <opt>none</opt>
+      <opt>clamp_0_inf</opt>
+      <opt>clamp_m1_1</opt>
+      <opt>clamp_0_1</opt>
+    </mod>
+  </ins>
+
+  <ins name="*FCLAMP.v2f16" pseudo="true">
+    <src start="0" mask="0xfb"/>
+    <mod name="clamp" start="15" size="2">
+      <opt>none</opt>
+      <opt>clamp_0_inf</opt>
+      <opt>clamp_m1_1</opt>
+      <opt>clamp_0_1</opt>
+    </mod>
+  </ins>
+
 </bifrost>

src/panfrost/bifrost/bi_lower_swizzle.c

@@ -33,6 +33,10 @@
 static void
 bi_lower_swizzle_16(bi_context *ctx, bi_instr *ins, unsigned src)
 {
+        /* Identity is ok */
+        if (ins->src[src].swizzle == BI_SWIZZLE_H01)
+                return;
+
         /* TODO: Use the opcode table and be a lot more methodical about this... */
         switch (ins->op) {
         /* Some instructions used with 16-bit data never have swizzles */
@@ -66,14 +70,24 @@ bi_lower_swizzle_16(bi_context *ctx, bi_instr *ins, unsigned src)
                     return;
             else
                     break;
+
+        /* We don't want to deal with reswizzling logic in modifier prop. Move
+         * the swizzle outside, it's easier for clamp propagation. */
+        case BI_OPCODE_FCLAMP_V2F16:
+        {
+                bi_builder b = bi_init_builder(ctx, bi_after_instr(ins));
+                bi_index dest = ins->dest[0];
+                bi_index tmp = bi_temp(ctx);
+
+                ins->dest[0] = tmp;
+                bi_swz_v2i16_to(&b, dest, bi_replace_index(ins->src[0], tmp));
+                return;
+        }
+
         default:
             return;
         }
 
-        /* Identity is ok (TODO: what about replicate only?) */
-        if (ins->src[src].swizzle == BI_SWIZZLE_H01)
-                return;
-
         /* If the instruction is scalar we can ignore the other component */
         if (ins->dest[0].swizzle == BI_SWIZZLE_H00 &&
                         ins->src[src].swizzle == BI_SWIZZLE_H00)

src/panfrost/bifrost/bi_opt_mod_props.c

@@ -157,19 +157,16 @@ bi_takes_clamp(bi_instr *I)
 }
 
 static bool
-bi_is_fclamp(bi_instr *I)
+bi_is_fclamp(enum bi_opcode op, enum bi_size size)
 {
-        return (I->op == BI_OPCODE_FADD_F32 || I->op == BI_OPCODE_FADD_V2F16) &&
+        return (size == BI_SIZE_32 && op == BI_OPCODE_FCLAMP_F32) ||
-                (!I->src[0].abs && !I->src[0].neg) &&
+               (size == BI_SIZE_16 && op == BI_OPCODE_FCLAMP_V2F16);
-                (I->src[1].type == BI_INDEX_CONSTANT && I->src[1].value == 0) &&
-                (I->clamp != BI_CLAMP_NONE);
 }
 
 static bool
 bi_optimizer_clamp(bi_instr *I, bi_instr *use)
 {
-        if (bi_opcode_props[use->op].size != bi_opcode_props[I->op].size) return false;
+        if (!bi_is_fclamp(use->op, bi_opcode_props[I->op].size)) return false;
-        if (!bi_is_fclamp(use)) return false;
         if (!bi_takes_clamp(I)) return false;
 
         /* Clamps are bitfields (clamp_m1_1/clamp_0_inf) so composition is OR */
@@ -260,6 +257,8 @@ bi_lower_opt_instruction(bi_instr *I)
         switch (I->op) {
         case BI_OPCODE_FABSNEG_F32:
         case BI_OPCODE_FABSNEG_V2F16:
+        case BI_OPCODE_FCLAMP_F32:
+        case BI_OPCODE_FCLAMP_V2F16:
                 I->op = (bi_opcode_props[I->op].size == BI_SIZE_32) ?
                         BI_OPCODE_FADD_F32 : BI_OPCODE_FADD_V2F16;
 

src/panfrost/bifrost/bifrost_compile.c

@@ -1862,19 +1862,19 @@ bi_emit_alu(bi_builder *b, nir_alu_instr *instr)
                 break;
 
         case nir_op_fsat: {
-                bi_instr *I = bi_fadd_to(b, sz, dst, s0, bi_negzero(), BI_ROUND_NONE);
+                bi_instr *I = bi_fclamp_to(b, sz, dst, s0);
                 I->clamp = BI_CLAMP_CLAMP_0_1;
                 break;
         }
 
         case nir_op_fsat_signed_mali: {
-                bi_instr *I = bi_fadd_to(b, sz, dst, s0, bi_negzero(), BI_ROUND_NONE);
+                bi_instr *I = bi_fclamp_to(b, sz, dst, s0);
                 I->clamp = BI_CLAMP_CLAMP_M1_1;
                 break;
         }
 
         case nir_op_fclamp_pos_mali: {
-                bi_instr *I = bi_fadd_to(b, sz, dst, s0, bi_negzero(), BI_ROUND_NONE);
+                bi_instr *I = bi_fclamp_to(b, sz, dst, s0);
                 I->clamp = BI_CLAMP_CLAMP_0_INF;
                 break;
         }