[clang] [llvm] [clang] Support the Swift calling convention on 32-bit PowerPC (PR #205457)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-powerpc

Author: Alsey Coleman Miller (colemancda)

<details>
<summary>Changes</summary>

Adds Swift calling-convention (swiftcc/swifttailcc) support to the 32-bit PowerPC SVR4/EABI target. Without it, clang aborts with "Swift ABI info has not been initialized" because the 32-bit PowerPC target registered no SwiftABIInfo, which prevents Swift (e.g. Embedded Swift) from targeting 32-bit PowerPC platforms such as the Nintendo Wii/GameCube (PPC750).

Mirrors the existing X86-32, ARM, AArch64 and 64-bit PowerPC handling.

---
Full diff: https://github.com/llvm/llvm-project/pull/205457.diff


3 Files Affected:

- (modified) clang/lib/Basic/Targets/PPC.h (+11) 
- (modified) clang/lib/CodeGen/Targets/PPC.cpp (+15-1) 
- (modified) llvm/lib/Target/PowerPC/PPCISelLowering.cpp (+4-3) 


``````````diff
diff --git a/clang/lib/Basic/Targets/PPC.h b/clang/lib/Basic/Targets/PPC.h
index e3bf5072d932d..165de12118eb8 100644
--- a/clang/lib/Basic/Targets/PPC.h
+++ b/clang/lib/Basic/Targets/PPC.h
@@ -433,6 +433,17 @@ class LLVM_LIBRARY_VISIBILITY PPC32TargetInfo : public PPCTargetInfo {
   std::pair<unsigned, unsigned> hardwareInterferenceSizes() const override {
     return std::make_pair(32, 32);
   }
+
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_Swift:
+      return CCCR_OK;
+    case CC_SwiftAsync:
+      return CCCR_Error;
+    default:
+      return CCCR_Warning;
+    }
+  }
 };
 
 // Note: ABI differences may eventually require us to have a separate
diff --git a/clang/lib/CodeGen/Targets/PPC.cpp b/clang/lib/CodeGen/Targets/PPC.cpp
index ab069bfbd1b51..9024f9934c37e 100644
--- a/clang/lib/CodeGen/Targets/PPC.cpp
+++ b/clang/lib/CodeGen/Targets/PPC.cpp
@@ -382,12 +382,26 @@ class PPC32_SVR4_ABIInfo : public DefaultABIInfo {
                    AggValueSlot Slot) const override;
 };
 
+/// Swift calling convention ABI for 32-bit PowerPC (SVR4/EABI).
+class PPC32SwiftABIInfo : public SwiftABIInfo {
+public:
+  explicit PPC32SwiftABIInfo(CodeGenTypes &CGT)
+      : SwiftABIInfo(CGT, /*SwiftErrorInRegister=*/false) {}
+
+  bool shouldPassIndirectly(ArrayRef<llvm::Type *> ComponentTys,
+                            bool AsReturnValue) const override {
+    return occupiesMoreThan(ComponentTys, /*total=*/4);
+  }
+};
+
 class PPC32TargetCodeGenInfo : public TargetCodeGenInfo {
 public:
   PPC32TargetCodeGenInfo(CodeGenTypes &CGT, bool SoftFloatABI,
                          bool RetSmallStructInRegABI)
       : TargetCodeGenInfo(std::make_unique<PPC32_SVR4_ABIInfo>(
-            CGT, SoftFloatABI, RetSmallStructInRegABI)) {}
+            CGT, SoftFloatABI, RetSmallStructInRegABI)) {
+    SwiftInfo = std::make_unique<PPC32SwiftABIInfo>(CGT);
+  }
 
   static bool isStructReturnInRegABI(const llvm::Triple &Triple,
                                      const CodeGenOptions &Opts);
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 76cc06f2b4ed9..1c30846a3182c 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -5978,9 +5978,10 @@ SDValue PPCTargetLowering::LowerCall_32SVR4(
   const bool IsVarArg = CFlags.IsVarArg;
   const bool IsTailCall = CFlags.IsTailCall;
 
-  assert((CallConv == CallingConv::C ||
-          CallConv == CallingConv::Cold ||
-          CallConv == CallingConv::Fast) && "Unknown calling convention!");
+  assert((CallConv == CallingConv::C || CallConv == CallingConv::Cold ||
+          CallConv == CallingConv::Fast || CallConv == CallingConv::Swift ||
+          CallConv == CallingConv::SwiftTail) &&
+         "Unknown calling convention!");
 
   const Align PtrAlign(4);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/205457