From a43e6addca7934f1f3aa60c029f80d20dabb1a3a Mon Sep 17 00:00:00 2001
From: Faith Ekstrand <faith.ekstrand@collabora.com>
Date: Tue, 10 Oct 2023 13:20:44 -0500
Subject: [PATCH] nak: Fix fneg to do fadd(-0, x)

Thanks to floating point sillyness, fadd(0, x) isn't a no-op but
fadd(-0, x) is.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24998>
---
 src/nouveau/compiler/nak_from_nir.rs      |  2 +-
 src/nouveau/compiler/nak_ir.rs            | 18 +++++++++++++++++-
 src/nouveau/compiler/nak_opt_copy_prop.rs |  4 ++--
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/nouveau/compiler/nak_from_nir.rs b/src/nouveau/compiler/nak_from_nir.rs
index 8648ee7e79e..084905bf058 100644
--- a/src/nouveau/compiler/nak_from_nir.rs
+++ b/src/nouveau/compiler/nak_from_nir.rs
@@ -360,7 +360,7 @@ impl<'a> ShaderFromNir<'a> {
                 let (x, y) = match alu.op {
                     nir_op_fabs => (srcs[0].fabs(), Src::new_zero()),
                     nir_op_fadd => (srcs[0], srcs[1]),
-                    nir_op_fneg => (srcs[0].fneg(), Src::new_zero()),
+                    nir_op_fneg => (Src::new_zero().fneg(), srcs[0].fneg()),
                     _ => panic!("Unhandled case"),
                 };
                 assert!(alu.def.bit_size() == 32);
diff --git a/src/nouveau/compiler/nak_ir.rs b/src/nouveau/compiler/nak_ir.rs
index 76f081d48a6..c7932bc4c5a 100644
--- a/src/nouveau/compiler/nak_ir.rs
+++ b/src/nouveau/compiler/nak_ir.rs
@@ -1088,7 +1088,23 @@ impl Src {
 
     pub fn is_zero(&self) -> bool {
         match self.src_ref {
-            SrcRef::Zero => true,
+            SrcRef::Zero | SrcRef::Imm32(0) => match self.src_mod {
+                SrcMod::None | SrcMod::FAbs | SrcMod::INeg => true,
+                SrcMod::FNeg | SrcMod::FNegAbs | SrcMod::BNot => false,
+            },
+            _ => false,
+        }
+    }
+
+    pub fn is_fneg_zero(&self, src_type: SrcType) -> bool {
+        match self.src_ref {
+            SrcRef::Zero | SrcRef::Imm32(0) => match self.src_mod {
+                SrcMod::FNeg | SrcMod::FNegAbs => true,
+                _ => false,
+            }
+            SrcRef::Imm32(0x80000000) => {
+                src_type == SrcType::F32 && self.src_mod.is_none()
+            }
             _ => false,
         }
     }
diff --git a/src/nouveau/compiler/nak_opt_copy_prop.rs b/src/nouveau/compiler/nak_opt_copy_prop.rs
index f0e7f17e54f..5b68914f879 100644
--- a/src/nouveau/compiler/nak_opt_copy_prop.rs
+++ b/src/nouveau/compiler/nak_opt_copy_prop.rs
@@ -313,9 +313,9 @@ impl CopyPropPass {
                         let dst = dst[0];
 
                         if !add.saturate {
-                            if add.srcs[0].is_zero() {
+                            if add.srcs[0].is_fneg_zero(SrcType::F32) {
                                 self.add_copy(dst, SrcType::F32, add.srcs[1]);
-                            } else if add.srcs[1].is_zero() {
+                            } else if add.srcs[1].is_fneg_zero(SrcType::F32) {
                                 self.add_copy(dst, SrcType::F32, add.srcs[0]);
                             }
                         }