From da9838e6c3500901120b1a6899839a4275eb589d Mon Sep 17 00:00:00 2001
From: Jim Blandy <jimb@red-bean.com>
Date: Fri, 2 Sep 2022 11:29:25 -0700
Subject: [PATCH] [spv-out] Don't emit no-op `OpBitCast` instructions.

As reported in #2015, some drivers trip over these.
---
 src/back/spv/block.rs          | 40 ++++++++++++++++++++++++++--------
 tests/out/spv/image.spvasm     |  3 +--
 tests/out/spv/operators.spvasm |  6 -----
 3 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/src/back/spv/block.rs b/src/back/spv/block.rs
index 8a388be22e..10fd5d72aa 100644
--- a/src/back/spv/block.rs
+++ b/src/back/spv/block.rs
@@ -1029,6 +1029,7 @@ impl<'w> BlockContext<'w> {
                     };
 
                 enum Cast {
+                    Identity,
                     Unary(spirv::Op),
                     Binary(spirv::Op, Word),
                     Ternary(spirv::Op, Word, Word),
@@ -1039,6 +1040,13 @@ impl<'w> BlockContext<'w> {
                     Cast::Unary(spirv::Op::CopyObject)
                 } else {
                     match (src_kind, kind, convert) {
+                        // Filter out identity casts. Some Adreno drivers are
+                        // confused by no-op OpBitCast instructions.
+                        (src_kind, kind, convert)
+                            if src_kind == kind && convert.unwrap_or(src_width) == src_width =>
+                        {
+                            Cast::Identity
+                        }
                         (Sk::Bool, Sk::Bool, _) => Cast::Unary(spirv::Op::CopyObject),
                         (_, _, None) => Cast::Unary(spirv::Op::Bitcast),
                         // casting to a bool - generate `OpXxxNotEqual`
@@ -1144,16 +1152,30 @@ impl<'w> BlockContext<'w> {
 
                 let id = self.gen_id();
                 let instruction = match cast {
-                    Cast::Unary(op) => Instruction::unary(op, result_type_id, id, expr_id),
-                    Cast::Binary(op, operand) => {
-                        Instruction::binary(op, result_type_id, id, expr_id, operand)
-                    }
-                    Cast::Ternary(op, op1, op2) => {
-                        Instruction::ternary(op, result_type_id, id, expr_id, op1, op2)
-                    }
+                    Cast::Identity => None,
+                    Cast::Unary(op) => Some(Instruction::unary(op, result_type_id, id, expr_id)),
+                    Cast::Binary(op, operand) => Some(Instruction::binary(
+                        op,
+                        result_type_id,
+                        id,
+                        expr_id,
+                        operand,
+                    )),
+                    Cast::Ternary(op, op1, op2) => Some(Instruction::ternary(
+                        op,
+                        result_type_id,
+                        id,
+                        expr_id,
+                        op1,
+                        op2,
+                    )),
                 };
-                block.body.push(instruction);
-                id
+                if let Some(instruction) = instruction {
+                    block.body.push(instruction);
+                    id
+                } else {
+                    expr_id
+                }
             }
             crate::Expression::ImageLoad {
                 image,
diff --git a/tests/out/spv/image.spvasm b/tests/out/spv/image.spvasm
index 7ad2b35603..f0556d35d4 100644
--- a/tests/out/spv/image.spvasm
+++ b/tests/out/spv/image.spvasm
@@ -277,8 +277,7 @@ OpFunctionEnd
 OpBranch %150
 %150 = OpLabel
 %152 = OpImageQuerySizeLod  %4  %143 %151
-%153 = OpBitcast  %4  %152
-%154 = OpImageQuerySizeLod  %4  %143 %153
+%154 = OpImageQuerySizeLod  %4  %143 %152
 %155 = OpImageQuerySizeLod  %21  %144 %151
 %156 = OpImageQuerySizeLod  %21  %144 %6
 %157 = OpImageQuerySizeLod  %105  %145 %151
diff --git a/tests/out/spv/operators.spvasm b/tests/out/spv/operators.spvasm
index 2e7cc31391..bdd3551109 100644
--- a/tests/out/spv/operators.spvasm
+++ b/tests/out/spv/operators.spvasm
@@ -161,13 +161,7 @@ OpStore %110 %118
 %129 = OpCompositeConstruct  %31  %5 %5
 %130 = OpCompositeConstruct  %32  %128 %129
 %131 = OpCompositeConstruct  %36  %11 %7 %18 %21
-%132 = OpCopyObject  %10  %12
-%133 = OpBitcast  %8  %11
-%134 = OpBitcast  %20  %19
-%135 = OpBitcast  %4  %5
-%136 = OpBitcast  %34  %46
 %137 = OpCopyObject  %37  %53
-%138 = OpBitcast  %34  %46
 %139 = OpCopyObject  %37  %53
 %142 = OpAccessChain  %141  %110 %19 %19
 %143 = OpLoad  %4  %142