[PATCH 0/2] llvm: improve default/zero initialization

[PATCH 0/2] llvm: improve default/zero initialization

[Luc Van Oostenryck]

This series contains:
- a fix for the default initialization of arrays and structures
- a small simplification for the initialization of null-pointers

This series is available in the Git repository at:
  git://github.com/lucvoo/sparse-dev.git llvm-zero-init

Luc Van Oostenryck (2):
  llvm: simplify emit of null pointers
  llvm: default init of arrays & structs

 sparse-llvm.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

-- 
2.15.0

[PATCH 1/2] llvm: simplify emit of null pointers

[Luc Van Oostenryck]

Most pointers with a constant value are simply null-pointers.
The only exception is when a known address is casted to pointer.

The current code only handle code for the general case:
emit code for a constant integer and then cast this to a pointer.
This obfuscate a bit the ouput, making it hard to read.

Change this by special handling the normal case of null-pointers
by directly using LLVM's LLVMConstPointerNull().

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 sparse-llvm.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/sparse-llvm.c b/sparse-llvm.c
index a8186df5b..4c64f1aaa 100644
--- a/sparse-llvm.c
+++ b/sparse-llvm.c
@@ -340,14 +340,16 @@ static LLVMValueRef get_sym_value(struct function *fn, struct symbol *sym)
 
 static LLVMValueRef constant_value(unsigned long long val, LLVMTypeRef dtype)
 {
-	LLVMTypeRef itype;
 	LLVMValueRef result;
 
 	switch (LLVMGetTypeKind(dtype)) {
 	case LLVMPointerTypeKind:
-		itype = LLVMIntType(bits_in_pointer);
-		result = LLVMConstInt(itype, val, 1);
-		result = LLVMConstIntToPtr(result, dtype);
+		if (val != 0) {	 // for example: ... = (void*) 0x123;
+			LLVMTypeRef itype = LLVMIntType(bits_in_pointer);
+			result = LLVMConstInt(itype, val, 1);
+			result = LLVMConstIntToPtr(result, dtype);
+		}
+		result = LLVMConstPointerNull(dtype);
 		break;
 	case LLVMIntegerTypeKind:
 		result = LLVMConstInt(dtype, val, 1);
-- 
2.15.0

[PATCH 2/2] llvm: default init of arrays & structs

[Luc Van Oostenryck]

Linearization of arrays & structs default initialization is done
as if these objects would be an integer as large as the object.
This integer is then simply zero-initialized.
(This may be objectionable and will be done differently).

However, sparse-llvm is not ready to handle this situation where
a non-scalar is initialized with a scalar value.

Workaround this by using LLVMConstNull() when possible.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 sparse-llvm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sparse-llvm.c b/sparse-llvm.c
index 4c64f1aaa..a1a48fd0f 100644
--- a/sparse-llvm.c
+++ b/sparse-llvm.c
@@ -354,6 +354,12 @@ static LLVMValueRef constant_value(unsigned long long val, LLVMTypeRef dtype)
 	case LLVMIntegerTypeKind:
 		result = LLVMConstInt(dtype, val, 1);
 		break;
+	case LLVMArrayTypeKind:
+	case LLVMStructTypeKind:
+		if (val != 0)
+			return NULL;
+		result = LLVMConstNull(dtype);
+		break;
 	default:
 		return NULL;
 	}
-- 
2.15.0