From 0b96fa88fd83d9f6ef91681695376f31ec64ad41 Mon Sep 17 00:00:00 2001
From: Jonah Williams <jonahwilliams@google.com>
Date: Wed, 26 Feb 2025 09:54:53 -0800
Subject: [PATCH] [Impeller] work around for crashy Nexus 5 Driver. (#164040)

Rewrites exp to work around crashes on Nexus 5.
---
 .../flutter/ci/licenses_golden/licenses_flutter  |  2 ++
 .../compiler/shader_lib/impeller/BUILD.gn        |  1 +
 .../compiler/shader_lib/impeller/math.glsl       | 16 ++++++++++++++++
 .../impeller/entity/shaders/rrect_blur.frag      |  7 ++++---
 engine/src/flutter/impeller/tools/malioc.json    |  2 +-
 5 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 engine/src/flutter/impeller/compiler/shader_lib/impeller/math.glsl

diff --git a/engine/src/flutter/ci/licenses_golden/licenses_flutter b/engine/src/flutter/ci/licenses_golden/licenses_flutter
index 7c45a24340..6848728c2e 100644
--- a/engine/src/flutter/ci/licenses_golden/licenses_flutter
+++ b/engine/src/flutter/ci/licenses_golden/licenses_flutter
@@ -41654,6 +41654,7 @@ ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/dithering.glsl +
 ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/external_texture_oes.glsl + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/gaussian.glsl + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/gradient.glsl + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/math.glsl + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/path.glsl + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/prefix_sum.glsl + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/compiler/shader_lib/impeller/texture.glsl + ../../../flutter/LICENSE
@@ -44568,6 +44569,7 @@ FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/dithering.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/external_texture_oes.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/gaussian.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/gradient.glsl
+FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/math.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/path.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/prefix_sum.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/texture.glsl
diff --git a/engine/src/flutter/impeller/compiler/shader_lib/impeller/BUILD.gn b/engine/src/flutter/impeller/compiler/shader_lib/impeller/BUILD.gn
index 08b2121ee5..1fc19bf293 100644
--- a/engine/src/flutter/impeller/compiler/shader_lib/impeller/BUILD.gn
+++ b/engine/src/flutter/impeller/compiler/shader_lib/impeller/BUILD.gn
@@ -13,6 +13,7 @@ copy("impeller") {
     "external_texture_oes.glsl",
     "gaussian.glsl",
     "gradient.glsl",
+    "math.glsl",
     "path.glsl",
     "texture.glsl",
     "tile_mode.glsl",
diff --git a/engine/src/flutter/impeller/compiler/shader_lib/impeller/math.glsl b/engine/src/flutter/impeller/compiler/shader_lib/impeller/math.glsl
new file mode 100644
index 0000000000..2c0651a1c2
--- /dev/null
+++ b/engine/src/flutter/impeller/compiler/shader_lib/impeller/math.glsl
@@ -0,0 +1,16 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MATH_GLSL_
+#define MATH_GLSL_
+
+// pow(x, y) crashes the shader compiler on the Nexus 5.
+// See also: https://skia-review.googlesource.com/c/skia/+/148480
+#ifdef IMPELLER_TARGET_OPENGLES
+#define POW(x, y) exp2(y* log2(x))
+#else
+#define POW(x, y) pow(x, y)
+#endif
+
+#endif  // MATH_GLSL_
diff --git a/engine/src/flutter/impeller/entity/shaders/rrect_blur.frag b/engine/src/flutter/impeller/entity/shaders/rrect_blur.frag
index d0bba43561..934262de90 100644
--- a/engine/src/flutter/impeller/entity/shaders/rrect_blur.frag
+++ b/engine/src/flutter/impeller/entity/shaders/rrect_blur.frag
@@ -9,6 +9,7 @@
 precision highp float;
 
 #include <impeller/gaussian.glsl>
+#include <impeller/math.glsl>
 #include <impeller/types.glsl>
 
 uniform FragInfo {
@@ -44,9 +45,9 @@ float computeErf7(float x) {
 
 // The length formula, but with an exponent other than 2
 float powerDistance(vec2 p) {
-  float xp = pow(p.x, frag_info.exponent);
-  float yp = pow(p.y, frag_info.exponent);
-  return pow(xp + yp, frag_info.exponentInv);
+  float xp = POW(p.x, frag_info.exponent);
+  float yp = POW(p.y, frag_info.exponent);
+  return POW(xp + yp, frag_info.exponentInv);
 }
 
 void main() {
diff --git a/engine/src/flutter/impeller/tools/malioc.json b/engine/src/flutter/impeller/tools/malioc.json
index ffdb6a6235..4502526e9a 100644
--- a/engine/src/flutter/impeller/tools/malioc.json
+++ b/engine/src/flutter/impeller/tools/malioc.json
@@ -4365,7 +4365,7 @@
           },
           "thread_occupancy": 100,
           "uniform_registers_used": 4,
-          "work_registers_used": 3
+          "work_registers_used": 2
         }
       }
     }