[PATCH] sparse, llvm: Fix 'void' return type code generation

[Pekka Enberg <penberg@kernel.org>]

Jonathan Neuschäfer reports:

  A simple function like this will compile to the following llvm
  bitcode:

        /* C */
        void func(void) {
                return;
        }

        /* LLVM */
        define i8 @func() {
        L0:
          ret void
        }

  The return type of the function and the type in the return instruction
  don't match.

  I found this inconsistency by running LLVM's bitcode validation on the
  bitcode produced by sparse-llvm.

Move 'void *' special-casing from sym_basetype_type() to sym_ptr_type()
to fix the issue.

Reported by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Cc: Christopher Li <sparse@chrisli.org>
Cc: Jeff Garzik <jgarzik@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
 sparse-llvm.c                         |   12 ++++++++++--
 validation/backend/void-return-type.c |   13 +++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)
 create mode 100644 validation/backend/void-return-type.c

diff --git a/sparse-llvm.c b/sparse-llvm.c
index e02e212..213d42d 100644
--- a/sparse-llvm.c
+++ b/sparse-llvm.c
@@ -150,7 +150,13 @@ static LLVMTypeRef sym_union_type(LLVMModuleRef module, struct symbol *sym)
 
 static LLVMTypeRef sym_ptr_type(LLVMModuleRef module, struct symbol *sym)
 {
-	LLVMTypeRef type = symbol_type(module, sym->ctype.base_type);
+	LLVMTypeRef type;
+
+	/* 'void *' is treated like 'char *' */
+	if (is_void_type(sym->ctype.base_type))
+		type = LLVMInt8Type();
+	else
+		type = symbol_type(module, sym->ctype.base_type);
 
 	return LLVMPointerType(type, 0);
 }
@@ -176,10 +182,12 @@ static LLVMTypeRef sym_basetype_type(struct symbol *sym)
 		}
 	} else {
 		switch (sym->bit_size) {
+		case -1:
+			ret = LLVMVoidType();
+			break;
 		case 1:
 			ret = LLVMInt1Type();
 			break;
-		case -1:	/* 'void *' is treated like 'char *' */
 		case 8:
 			ret = LLVMInt8Type();
 			break;
diff --git a/validation/backend/void-return-type.c b/validation/backend/void-return-type.c
new file mode 100644
index 0000000..b282fde
--- /dev/null
+++ b/validation/backend/void-return-type.c
@@ -0,0 +1,13 @@
+static void foo(void)
+{
+}
+
+static void *bar(void *p)
+{
+	return p;
+}
+
+/*
+ * check-name: void return type code generation
+ * check-command: ./sparsec -c $file -o tmp.o
+ */
-- 
1.7.7.6

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