Mesa (main): pan/bi: Avoid *FADD.v2f16 hazard in scheduler

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Module: Mesa
Branch: main
Commit: 24d2bdb1e050134a25924487792ee0018f8478ae
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=24d2bdb1e050134a25924487792ee0018f8478ae

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Thu Feb 17 19:34:04 2022 -0500

pan/bi: Avoid *FADD.v2f16 hazard in scheduler

Obscure encoding restriction. Fixes crash (assertion fail when instruction
packing) in asphalt9/2659.shader_test on Bifrost.

Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15072>

---

 src/panfrost/bifrost/bi_schedule.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/panfrost/bifrost/bi_schedule.c b/src/panfrost/bifrost/bi_schedule.c
index 88162ecc86e..4c6770e7719 100644
--- a/src/panfrost/bifrost/bi_schedule.c
+++ b/src/panfrost/bifrost/bi_schedule.c
@@ -490,6 +490,18 @@ bi_can_iaddc(bi_instr *ins)
                 ins->src[1].swizzle == BI_SWIZZLE_H01);
 }
 
+/*
+ * The encoding of *FADD.v2f16 only specifies a single abs flag. All abs
+ * encodings are permitted by swapping operands; however, this scheme fails if
+ * both operands are equal. Test for this case.
+ */
+static bool
+bi_impacted_abs(bi_instr *I)
+{
+        return I->src[0].abs && I->src[1].abs &&
+               bi_is_word_equiv(I->src[0], I->src[1]);
+}
+
 bool
 bi_can_fma(bi_instr *ins)
 {
@@ -497,6 +509,10 @@ bi_can_fma(bi_instr *ins)
         if (bi_can_iaddc(ins))
                 return true;
 
+        /* *FADD.v2f16 has restricted abs modifiers, use +FADD.v2f16 instead */
+        if (ins->op == BI_OPCODE_FADD_V2F16 && bi_impacted_abs(ins))
+                return false;
+
         /* TODO: some additional fp16 constraints */
         return bi_opcode_props[ins->op].fma;
 }