Add a known bounds optimization to ASan.

test/Instrumentation/AddressSanitizer/OptKnownBounds/heap-free.ll

+; Invalid access of a freed heap object.
+
+; RUN: opt < %s -asan -S -asan-opt=1 -asan-opt-known-bounds=1 | FileCheck %s -check-prefix=OPT1
+; RUN: opt < %s -asan -S -asan-opt=0 | FileCheck %s -check-prefix=OPT0
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define noalias i32* @example(i64 %n) address_safety nounwind uwtable {
+entry:
+  %call = tail call noalias i8* @malloc(i64 200) nounwind
+  %0 = bitcast i8* %call to i32*
+  tail call void @free(i8* %call) nounwind
+  %conv = trunc i64 %n to i32
+  %arrayidx = getelementptr inbounds i8* %call, i64 12
+  %1 = bitcast i8* %arrayidx to i32*
+  store i32 %conv, i32* %1, align 4
+  ret i32* %0
+}
+
+declare noalias i8* @malloc(i64) nounwind
+
+declare void @free(i8* nocapture) nounwind
+
+; OPT1: @example
+; OPT1: call void @__asan_report_
+; OPT1-NOT: call void @__asan_report_
+; OPT1: @asan.module_ctor
+
+; OPT0: @example
+; OPT0: call void @__asan_report_
+; OPT0-NOT: call void @__asan_report_
+; OPT0: @asan.module_ctor
+
+; C-example: #include <stdlib.h>
+; C-example:
+; C-example: int* example(size_t n) {
+; C-example:   int *array = malloc(50 * sizeof(int));
+; C-example:   free(array);
+; C-example:   array[3] = n;  // BUG
+; C-example:   return array;
+; C-example: }