A key design point of an SSA-based representation is how it represents memory. In LLVM, no memory locations are in SSA form, which makes things - very simple. This section describes how to read, write, allocate, and free + very simple. This section describes how to read, write, and allocate memory in LLVM.
- - - -
- <result> = malloc <type>[, i32 <NumElements>][, align <alignment>] ; yields {type*}:result
-
-
-The 'malloc' instruction allocates memory from the system heap and - returns a pointer to it. The object is always allocated in the generic - address space (address space zero).
- -The 'malloc' instruction allocates - sizeof(<type>)*NumElements bytes of memory from the operating - system and returns a pointer of the appropriate type to the program. If - "NumElements" is specified, it is the number of elements allocated, otherwise - "NumElements" is defaulted to be one. If a constant alignment is specified, - the value result of the allocation is guaranteed to be aligned to at least - that boundary. If not specified, or if zero, the target can choose to align - the allocation on any convenient boundary compatible with the type.
- -'type' must be a sized type.
- -Memory is allocated using the system "malloc" function, and a - pointer is returned. The result of a zero byte allocation is undefined. The - result is null if there is insufficient memory available.
- -
- %array = malloc [4 x i8] ; yields {[%4 x i8]*}:array
-
- %size = add i32 2, 2 ; yields {i32}:size = i32 4
- %array1 = malloc i8, i32 4 ; yields {i8*}:array1
- %array2 = malloc [12 x i8], i32 %size ; yields {[12 x i8]*}:array2
- %array3 = malloc i32, i32 4, align 1024 ; yields {i32*}:array3
- %array4 = malloc i32, align 1024 ; yields {i32*}:array4
-
-
-Note that the code generator does not yet respect the alignment value.
- -
- free <type> <value> ; yields {void}
-
-
-The 'free' instruction returns memory back to the unused memory heap - to be reallocated in the future.
- -'value' shall be a pointer value that points to a value that was - allocated with the 'malloc' instruction.
- -Access to the memory pointed to by the pointer is no longer defined after - this instruction executes. If the pointer is null, the operation is a - noop.
- -- %array = malloc [4 x i8] ; yields {[4 x i8]*}:array - free [4 x i8]* %array -- -
-%ptr = malloc i32
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
store i32 4, %ptr
%result1 = load i32* %ptr ; yields {i32}:result1 = 4
@@ -6675,7 +6592,8 @@ LLVM.
Examples:
-%ptr = malloc i32
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
store i32 4, %ptr
%val1 = add i32 4, 4
@@ -6730,7 +6648,8 @@ LLVM.
Examples:
-%ptr = malloc i32
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
store i32 4, %ptr
%val1 = add i32 4, 4
@@ -6785,8 +6704,9 @@ LLVM.
Examples:
-%ptr = malloc i32
- store i32 4, %ptr
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
+ store i32 4, %ptr
%result1 = call i32 @llvm.atomic.load.add.i32.p0i32( i32* %ptr, i32 4 )
; yields {i32}:result1 = 4
%result2 = call i32 @llvm.atomic.load.add.i32.p0i32( i32* %ptr, i32 2 )
@@ -6836,8 +6756,9 @@ LLVM.
Examples:
-%ptr = malloc i32
- store i32 8, %ptr
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
+ store i32 8, %ptr
%result1 = call i32 @llvm.atomic.load.sub.i32.p0i32( i32* %ptr, i32 4 )
; yields {i32}:result1 = 8
%result2 = call i32 @llvm.atomic.load.sub.i32.p0i32( i32* %ptr, i32 2 )
@@ -6913,8 +6834,9 @@ LLVM.
Examples:
-%ptr = malloc i32
- store i32 0x0F0F, %ptr
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
+ store i32 0x0F0F, %ptr
%result0 = call i32 @llvm.atomic.load.nand.i32.p0i32( i32* %ptr, i32 0xFF )
; yields {i32}:result0 = 0x0F0F
%result1 = call i32 @llvm.atomic.load.and.i32.p0i32( i32* %ptr, i32 0xFF )
@@ -6991,8 +6913,9 @@ LLVM.
Examples:
-%ptr = malloc i32
- store i32 7, %ptr
+%mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
+%ptr = bitcast i8* %mallocP to i32*
+ store i32 7, %ptr
%result0 = call i32 @llvm.atomic.load.min.i32.p0i32( i32* %ptr, i32 -2 )
; yields {i32}:result0 = 7
%result1 = call i32 @llvm.atomic.load.max.i32.p0i32( i32* %ptr, i32 8 )