From cde457ceddb4a34b821df5e5c8b6c76835a638dc Mon Sep 17 00:00:00 2001
From: Teodor Tanasoaia <28601907+teoxoy@users.noreply.github.com>
Date: Mon, 20 Feb 2023 21:40:26 +0100
Subject: [PATCH] [spv-out] fix `countLeadingZeros` impl (#2258)

---
 src/back/spv/block.rs               | 25 +++++++------------------
 tests/out/spv/math-functions.spvasm | 26 ++++++++++++--------------
 2 files changed, 19 insertions(+), 32 deletions(-)

diff --git a/src/back/spv/block.rs b/src/back/spv/block.rs
index 11d5782633..bf45130adf 100644
--- a/src/back/spv/block.rs
+++ b/src/back/spv/block.rs
@@ -951,33 +951,22 @@ impl<'w> BlockContext<'w> {
                             _ => unreachable!(),
                         };
 
+                        let msb_id = self.gen_id();
                         block.body.push(Instruction::ext_inst(
                             self.writer.gl450_ext_inst_id,
                             spirv::GLOp::FindUMsb,
                             int_type_id,
-                            id,
+                            msb_id,
                             &[arg0_id],
                         ));
 
-                        let sub_id = self.gen_id();
-                        block.body.push(Instruction::binary(
+                        MathOp::Custom(Instruction::binary(
                             spirv::Op::ISub,
-                            int_type_id,
-                            sub_id,
-                            int_id,
+                            result_type_id,
                             id,
-                        ));
-
-                        if let Some(crate::ScalarKind::Uint) = arg_scalar_kind {
-                            block.body.push(Instruction::unary(
-                                spirv::Op::Bitcast,
-                                result_type_id,
-                                self.gen_id(),
-                                sub_id,
-                            ));
-                        }
-
-                        return Ok(());
+                            int_id,
+                            msb_id,
+                        ))
                     }
                     Mf::CountOneBits => MathOp::Custom(Instruction::unary(
                         spirv::Op::BitCount,
diff --git a/tests/out/spv/math-functions.spvasm b/tests/out/spv/math-functions.spvasm
index d1a98b4e43..9dbde7ddf0 100644
--- a/tests/out/spv/math-functions.spvasm
+++ b/tests/out/spv/math-functions.spvasm
@@ -1,7 +1,7 @@
 ; SPIR-V
 ; Version: 1.1
 ; Generator: rspirv
-; Bound: 78
+; Bound: 76
 OpCapability Shader
 %1 = OpExtInstImport "GLSL.std.450"
 OpMemoryModel Logical GLSL450
@@ -28,7 +28,7 @@ OpEntryPoint Vertex %18 "main"
 %50 = OpTypeVector %9 2
 %53 = OpConstantComposite  %50  %42 %42
 %65 = OpConstant  %7  31
-%72 = OpConstantComposite  %15  %65 %65
+%71 = OpConstantComposite  %15  %65 %65
 %31 = OpConstantNull  %7
 %18 = OpFunction  %2  None %19
 %17 = OpLabel
@@ -71,17 +71,15 @@ OpBranch %20
 %61 = OpCompositeConstruct  %15  %13 %13
 %63 = OpExtInst  %15  %1 FindILsb %61
 %62 = OpExtInst  %15  %1 UMin %53 %63
-%64 = OpExtInst  %7  %1 FindUMsb %11
-%66 = OpISub  %7  %65 %64
-%67 = OpExtInst  %7  %1 FindUMsb %12
-%68 = OpISub  %7  %65 %67
-%69 = OpBitcast  %9  %68
-%70 = OpCompositeConstruct  %15  %11 %11
-%71 = OpExtInst  %15  %1 FindUMsb %70
-%73 = OpISub  %15  %72 %71
-%74 = OpCompositeConstruct  %50  %12 %12
-%75 = OpExtInst  %15  %1 FindUMsb %74
-%76 = OpISub  %15  %72 %75
-%77 = OpBitcast  %50  %76
+%66 = OpExtInst  %7  %1 FindUMsb %11
+%64 = OpISub  %7  %65 %66
+%68 = OpExtInst  %7  %1 FindUMsb %12
+%67 = OpISub  %9  %65 %68
+%69 = OpCompositeConstruct  %15  %11 %11
+%72 = OpExtInst  %15  %1 FindUMsb %69
+%70 = OpISub  %15  %71 %72
+%73 = OpCompositeConstruct  %50  %12 %12
+%75 = OpExtInst  %15  %1 FindUMsb %73
+%74 = OpISub  %50  %71 %75
 OpReturn
 OpFunctionEnd
\ No newline at end of file