Fix PR3754: don't mark functions that wrap MallocInst with

the readnone.  Since MallocInst is scheduled for deletion
it doesn't seem worth doing anything more subtle, such as
having mayWriteToMemory return true for MallocInst.

llvm-svn: 71077

lib/Transforms/IPO/FunctionAttrs.cpp

@@ -152,6 +152,11 @@ bool FunctionAttrs::AddReadAttrs(const std::vector<CallGraphNode *> &SCC) {
       if (I->mayWriteToMemory())
         // Writes memory.  Just give up.
         return false;
+
+      if (isa<MallocInst>(I))
+        // MallocInst claims not to write memory!  PR3754.
+        return false;
+
       // If this instruction may read memory, remember that.
       ReadsMemory |= I->mayReadFromMemory();
     }

test/Transforms/FunctionAttrs/2009-05-06-Malloc.ll

@@ -0,0 +1,7 @@
+; RUN: llvm-as < %s | opt -functionattrs | llvm-dis | not grep read
+; PR3754
+
+define i8* @m(i32 %size) {
+	%tmp = malloc i8, i32 %size		; <i8*> [#uses=1]
+	ret i8* %tmp
+}