From 49d7da52b6141b4788dba810f03af76a9b1551d5 Mon Sep 17 00:00:00 2001
From: Jed Brown <jed@jedbrown.org>
Date: Wed, 29 Jan 2014 22:31:22 -0700
Subject: [PATCH] PetscMalloc: allow ptr=malloc(0) and free(ptr)
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  ISO C90 §7.10.3: "If the size of the space requested is zero, the
  behavior is implementation-defined; the value returned shall be either
  a null pointer or a unique pointer."

We believe that ptr=malloc(0) and free(ptr) is now handled properly, so
it's no longer necessary to short-circuit our PetscMalloc.  This allows
memory checking tools to match size-0 allocations and frees if they so
choose.
---
 include/petscsys.h   | 14 ++++++++------
 src/sys/memory/mtr.c |  7 +------
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/include/petscsys.h b/include/petscsys.h
index d537197bf4a..674ce1e4bff 100644
--- a/include/petscsys.h
+++ b/include/petscsys.h
@@ -516,17 +516,17 @@ PETSC_EXTERN PetscErrorCode PetscCommDestroy(MPI_Comm*);
 
    Level: beginner
 
-   Notes: Memory is always allocated at least double aligned
+   Notes:
+   Memory is always allocated at least double aligned
 
-          If you request memory of zero size it will allocate no space and assign the pointer to 0; PetscFree() will
-          properly handle not freeing the null pointer.
+   It is safe to allocate size 0 and pass the resulting pointer (which may or may not be NULL) to PetscFree().
 
 .seealso: PetscFree(), PetscNew()
 
   Concepts: memory allocation
 
 M*/
-#define PetscMalloc(a,b)  ((a != 0) ? (*PetscTrMalloc)((a),__LINE__,PETSC_FUNCTION_NAME,__FILE__,(void**)(b)) : (*(b) = 0,0) )
+#define PetscMalloc(a,b)  ((*PetscTrMalloc)((a),__LINE__,PETSC_FUNCTION_NAME,__FILE__,(void**)(b)))
 
 /*MC
    PetscAddrAlign - Rounds up an address to PETSC_MEMALIGN alignment
@@ -1072,14 +1072,16 @@ M*/
 
    Level: beginner
 
-   Notes: Memory must have been obtained with PetscNew() or PetscMalloc()
+   Notes:
+   Memory must have been obtained with PetscNew() or PetscMalloc().
+   It is safe to call PetscFree() on a NULL pointer.
 
 .seealso: PetscNew(), PetscMalloc(), PetscFreeVoid()
 
   Concepts: memory allocation
 
 M*/
-#define PetscFree(a)   ((a) && ((*PetscTrFree)((void*)(a),__LINE__,PETSC_FUNCTION_NAME,__FILE__) || ((a) = 0,0)))
+#define PetscFree(a)   ((*PetscTrFree)((void*)(a),__LINE__,PETSC_FUNCTION_NAME,__FILE__) || ((a) = 0,0))
 
 /*MC
    PetscFreeVoid - Frees memory
diff --git a/src/sys/memory/mtr.c b/src/sys/memory/mtr.c
index fac91b2df60..05cd3bfb852 100644
--- a/src/sys/memory/mtr.c
+++ b/src/sys/memory/mtr.c
@@ -176,8 +176,6 @@ PetscErrorCode  PetscTrMallocDefault(size_t a,int lineno,const char function[],c
   PetscErrorCode ierr;
 
   PetscFunctionBegin;
-  if (!a) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Trying to malloc zero size array");
-
   if (TRdebugLevel) {
     ierr = PetscMallocValidate(lineno,function,filename); if (ierr) PetscFunctionReturn(ierr);
   }
@@ -257,10 +255,7 @@ PetscErrorCode  PetscTrFreeDefault(void *aa,int line,const char function[],const
 
   PetscFunctionBegin;
   /* Do not try to handle empty blocks */
-  if (!a) {
-    (*PetscErrorPrintf)("PetscTrFreeDefault called from %s() line %d in %s\n",function,line,file);
-    SETERRQ3(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Trying to free null block: Free called from %s() line %d in %s\n",function,line,file);
-  }
+  if (!a) PetscFunctionReturn(0);
 
   if (TRdebugLevel) {
     ierr = PetscMallocValidate(line,function,file);CHKERRQ(ierr);