[llvm] [DirectX] Move triple/DL compat to bitcode writer (PR #163587)

[Justin Bogner via llvm-commits]

https://github.com/bogner created https://github.com/llvm/llvm-project/pull/163587

Move our handling of setting up a compatible triple for DXIL to the bitcode writer itself, and do the same for the datalayout. This avoids us needing to temporarily change the triple just to change it back, and it also allows us to make the datalayout truly compatible, including the `i8:32` alignment that isn't accepted by modern LLVM's DataLayout.

>From 90b2f8e9f6c961d4c95366f0163a9cab2e88920f Mon Sep 17 00:00:00 2001
From: Justin Bogner <mail at justinbogner.com>
Date: Wed, 15 Oct 2025 10:18:59 -0600
Subject: [PATCH] [DirectX] Move triple/DL compat to bitcode writer

Move our handling of setting up a compatible triple for DXIL to the
bitcode writer itself, and do the same for the datalayout. This avoids
us needing to temporarily change the triple just to change it back, and
it also allows us to make the datalayout truly compatible, including the
`i8:32` alignment that isn't accepted by modern LLVM's DataLayout.
---
 .../DirectX/DXILWriter/DXILBitcodeWriter.cpp      | 15 +++++++++------
 .../Target/DirectX/DXILWriter/DXILWriterPass.cpp  |  8 --------
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/Target/DirectX/DXILWriter/DXILBitcodeWriter.cpp b/llvm/lib/Target/DirectX/DXILWriter/DXILBitcodeWriter.cpp
index 82c43ff8dc352..26a8728e1f37c 100644
--- a/llvm/lib/Target/DirectX/DXILWriter/DXILBitcodeWriter.cpp
+++ b/llvm/lib/Target/DirectX/DXILWriter/DXILBitcodeWriter.cpp
@@ -1165,12 +1165,15 @@ void DXILBitcodeWriter::writeValueSymbolTableForwardDecl() {}
 /// Returns the bit offset to backpatch with the location of the real VST.
 void DXILBitcodeWriter::writeModuleInfo() {
   // Emit various pieces of data attached to a module.
-  if (!M.getTargetTriple().empty())
-    writeStringRecord(Stream, bitc::MODULE_CODE_TRIPLE,
-                      M.getTargetTriple().str(), 0 /*TODO*/);
-  const std::string &DL = M.getDataLayoutStr();
-  if (!DL.empty())
-    writeStringRecord(Stream, bitc::MODULE_CODE_DATALAYOUT, DL, 0 /*TODO*/);
+
+  // We need to hardcode a triple and datalayout that's compatible with the
+  // historical DXIL triple and datalayout from DXC.
+  StringRef Triple = "dxil-ms-dx";
+  StringRef DL = "e-m:e-p:32:32-i1:8-i8:8-i16:32-i32:32-i64:64-"
+                 "f16:32-f32:32-f64:64-n8:16:32:64";
+  writeStringRecord(Stream, bitc::MODULE_CODE_TRIPLE, Triple, 0 /*TODO*/);
+  writeStringRecord(Stream, bitc::MODULE_CODE_DATALAYOUT, DL, 0 /*TODO*/);
+
   if (!M.getModuleInlineAsm().empty())
     writeStringRecord(Stream, bitc::MODULE_CODE_ASM, M.getModuleInlineAsm(),
                       0 /*TODO*/);
diff --git a/llvm/lib/Target/DirectX/DXILWriter/DXILWriterPass.cpp b/llvm/lib/Target/DirectX/DXILWriter/DXILWriterPass.cpp
index 1eb03bfc087e3..725f2b1e7c76c 100644
--- a/llvm/lib/Target/DirectX/DXILWriter/DXILWriterPass.cpp
+++ b/llvm/lib/Target/DirectX/DXILWriter/DXILWriterPass.cpp
@@ -149,11 +149,6 @@ class EmbedDXILPass : public llvm::ModulePass {
     std::string Data;
     llvm::raw_string_ostream OS(Data);
 
-    Triple OriginalTriple = M.getTargetTriple();
-    // Set to DXIL triple when write to bitcode.
-    // Only the output bitcode need to be DXIL triple.
-    M.setTargetTriple(Triple("dxil-ms-dx"));
-
     // Perform late legalization of lifetime intrinsics that would otherwise
     // fail the Module Verifier if performed in an earlier pass
     legalizeLifetimeIntrinsics(M);
@@ -165,9 +160,6 @@ class EmbedDXILPass : public llvm::ModulePass {
     // not-so-legal legalizations
     removeLifetimeIntrinsics(M);
 
-    // Recover triple.
-    M.setTargetTriple(OriginalTriple);
-
     Constant *ModuleConstant =
         ConstantDataArray::get(M.getContext(), arrayRefFromStringRef(Data));
     auto *GV = new llvm::GlobalVariable(M, ModuleConstant->getType(), true,