From d6ff9cd4390fa65994b9cd09efbccca7b6584f4c Mon Sep 17 00:00:00 2001
From: Ashley Hauck <github@khyperia.com>
Date: Tue, 30 Mar 2021 09:44:01 +0200
Subject: [PATCH] Run DCE twice (#556)

---
 crates/rustc_codegen_spirv/src/linker/mod.rs |  5 ++++-
 crates/spirv-builder/src/test/basic.rs       | 17 ++++++++---------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/crates/rustc_codegen_spirv/src/linker/mod.rs b/crates/rustc_codegen_spirv/src/linker/mod.rs
index f58cbe5e09..984bad65f0 100644
--- a/crates/rustc_codegen_spirv/src/linker/mod.rs
+++ b/crates/rustc_codegen_spirv/src/linker/mod.rs
@@ -277,7 +277,10 @@ pub fn link(sess: &Session, mut inputs: Vec<Module>, opts: &Options) -> Result<L
                 .write_all(spirv_tools::binary::from_binary(&output.assemble()))
                 .unwrap();
         }
-        if opts.dce && opts.emit_multiple_modules {
+        // Run DCE again, even if emit_multiple_modules==false - the first DCE ran before
+        // structurization and mem2reg (for perf reasons), and mem2reg may remove references to
+        // invalid types, so we need to DCE again.
+        if opts.dce {
             let _timer = sess.timer("link_dce_2");
             dce::dce(output);
         }
diff --git a/crates/spirv-builder/src/test/basic.rs b/crates/spirv-builder/src/test/basic.rs
index a3571bd984..c90e8dd693 100644
--- a/crates/spirv-builder/src/test/basic.rs
+++ b/crates/spirv-builder/src/test/basic.rs
@@ -189,15 +189,14 @@ OpDecorate %5 Binding 0
 %6 = OpTypeVoid
 %7 = OpTypeFunction %6
 %8 = OpTypeInt 32 0
-%9 = OpTypePointer Function %8
-%10 = OpConstant %8 1
-%11 = OpTypeFloat 32
-%12 = OpTypeImage %11 2D 0 0 0 1 Unknown
-%13 = OpTypeSampledImage %12
-%4 = OpTypeRuntimeArray %13
-%14 = OpTypePointer UniformConstant %4
-%5 = OpVariable %14 UniformConstant
-%15 = OpTypePointer UniformConstant %13"#,
+%9 = OpConstant %8 1
+%10 = OpTypeFloat 32
+%11 = OpTypeImage %10 2D 0 0 0 1 Unknown
+%12 = OpTypeSampledImage %11
+%4 = OpTypeRuntimeArray %12
+%13 = OpTypePointer UniformConstant %4
+%5 = OpVariable %13 UniformConstant
+%14 = OpTypePointer UniformConstant %12"#,
     );
 }