Subzero: Elide checks of known valid accesses of locals

tests_lit/asan_tests/instrumentload.ll

 ; Test for a call to __asan_check() preceding loads
 
 ; REQUIRES: allow_dump
 
 ; RUN: %p2i -i %s --args -verbose=inst -threads=0 -fsanitize-address \
 ; RUN:     | FileCheck --check-prefix=DUMP %s
 
 ; Constants to load data from
 @srcConst8 = internal constant [1 x i8] c"D"
 @srcConst16 = internal constant [2 x i8] c"DA"
 @srcConst32 = internal constant [4 x i8] c"DATA"
 @srcConst64 = internal constant [8 x i8] c"DATADATA"
 @srcConst128 = internal constant [16 x i8] c"DATADATADATADATA"
 
 ; A global to load data from
 @srcGlobal8 = internal global [1 x i8] c"D"
 @srcGlobal16 = internal global [2 x i8] c"DA"
 @srcGlobal32 = internal global [4 x i8] c"DATA"
 @srcGlobal64 = internal global [8 x i8] c"DATADATA"
 @srcGlobal128 = internal global [16 x i8] c"DATADATADATADATA"
 
 ; A function with a local variable that does the loads
-define internal void @doLoads() {
-  %srcLocal8 = alloca i8, i32 1, align 4
-  %srcLocal16 = alloca i8, i32 2, align 4
-  %srcLocal32 = alloca i8, i32 4, align 4
-  %srcLocal64 = alloca i8, i32 8, align 4
-  %srcLocal128 = alloca i8, i32 16, align 4
+define internal void @doLoads(i8* %srcLocal8, i16* %srcLocal16,

[Jim Stichnoth, 2016/07/26 12:49:26]

This actually isn't valid PNaCl bitcode.

Pointer args should actually be passed as i32 args, and then converted inside
the function via inttoptr instructions.

A word of caution though.  Once you add explicit pointer cast instructions to
the .ll file, you can get slightly different input/output depending on how
Subzero is run.  If you run "pnacl-sz foo.ll" directly on the .ll file, Subzero
will see inttoptr/ptrtoint instructions as integer assignment instructions.  If
you run the %p2i pipeline in a lit test, the inttoptr/ptrtoint instructions
disappear completely and Subzero never sees them.  Just mentioning this in case
you get into a situation where everything looks good run manually but
inexplicably fails as a lit test.

[tlively, 2016/07/26 17:58:53]

Done. This is good to know.

+                              i32* %srcLocal32, i64* %srcLocal64,
+                              <4 x i32>* %srcLocal128) {
 
   %ptrConst8 = bitcast [1 x i8]* @srcConst8 to i8*
   %ptrConst16 = bitcast [2 x i8]* @srcConst16 to i16*
   %ptrConst32 = bitcast [4 x i8]* @srcConst32 to i32*
   %ptrConst64 = bitcast [8 x i8]* @srcConst64 to i64*
   %ptrConst128 = bitcast [16 x i8]* @srcConst128 to <4 x i32>*
 
   %ptrGlobal8 = bitcast [1 x i8]* @srcGlobal8 to i8*
   %ptrGlobal16 = bitcast [2 x i8]* @srcGlobal16 to i16*
   %ptrGlobal32 = bitcast [4 x i8]* @srcGlobal32 to i32*
   %ptrGlobal64 = bitcast [8 x i8]* @srcGlobal64 to i64*
   %ptrGlobal128 = bitcast [16 x i8]* @srcGlobal128 to <4 x i32>*
 
-  %ptrLocal8 = bitcast i8* %srcLocal8 to i8*
-  %ptrLocal16 = bitcast i8* %srcLocal16 to i16*
-  %ptrLocal32 = bitcast i8* %srcLocal32 to i32*
-  %ptrLocal64 = bitcast i8* %srcLocal64 to i64*
-  %ptrLocal128 = bitcast i8* %srcLocal128 to <4 x i32>*
-
   %dest1 = load i8, i8* %ptrConst8, align 1
   %dest2 = load i16, i16* %ptrConst16, align 1
   %dest3 = load i32, i32* %ptrConst32, align 1
   %dest4 = load i64, i64* %ptrConst64, align 1
   %dest5 = load <4 x i32>, <4 x i32>* %ptrConst128, align 4
 
   %dest6 = load i8, i8* %ptrGlobal8, align 1
   %dest7 = load i16, i16* %ptrGlobal16, align 1
   %dest8 = load i32, i32* %ptrGlobal32, align 1
   %dest9 = load i64, i64* %ptrGlobal64, align 1
   %dest10 = load <4 x i32>, <4 x i32>* %ptrGlobal128, align 4
 
-  %dest11 = load i8, i8* %ptrLocal8, align 1
-  %dest12 = load i16, i16* %ptrLocal16, align 1
-  %dest13 = load i32, i32* %ptrLocal32, align 1
-  %dest14 = load i64, i64* %ptrLocal64, align 1
-  %dest15 = load <4 x i32>, <4 x i32>* %ptrLocal128, align 4
+  %dest11 = load i8, i8* %srcLocal8, align 1
+  %dest12 = load i16, i16* %srcLocal16, align 1
+  %dest13 = load i32, i32* %srcLocal32, align 1
+  %dest14 = load i64, i64* %srcLocal64, align 1
+  %dest15 = load <4 x i32>, <4 x i32>* %srcLocal128, align 4
 
   ret void
 }
 
 ; DUMP-LABEL: ================ Instrumented CFG ================
-; DUMP-NEXT: define internal void @doLoads() {
+; DUMP-NEXT: define internal void @doLoads(
 ; DUMP-NEXT: __0:
-; DUMP:      call void @__asan_check_load(i32 @srcConst8, i32 1)
+; DUMP-NEXT: call void @__asan_check_load(i32 @srcConst8, i32 1)
 ; DUMP-NEXT: %dest1 = load i8, i8* @srcConst8, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 @srcConst16, i32 2)
 ; DUMP-NEXT: %dest2 = load i16, i16* @srcConst16, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 @srcConst32, i32 4)
 ; DUMP-NEXT: %dest3 = load i32, i32* @srcConst32, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 @srcConst64, i32 8)
 ; DUMP-NEXT: %dest4 = load i64, i64* @srcConst64, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 @srcConst128, i32 16)
 ; DUMP-NEXT: %dest5 = load <4 x i32>, <4 x i32>* @srcConst128, align 4
 ; DUMP-NEXT: call void @__asan_check_load(i32 @srcGlobal8, i32 1)
@@ skipping 11 matching lines @@
 ; DUMP-NEXT: call void @__asan_check_load(i32 %srcLocal16, i32 2)
 ; DUMP-NEXT: %dest12 = load i16, i16* %srcLocal16, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 %srcLocal32, i32 4)
 ; DUMP-NEXT: %dest13 = load i32, i32* %srcLocal32, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 %srcLocal64, i32 8)
 ; DUMP-NEXT: %dest14 = load i64, i64* %srcLocal64, align 1
 ; DUMP-NEXT: call void @__asan_check_load(i32 %srcLocal128, i32 16)
 ; DUMP-NEXT: %dest15 = load <4 x i32>, <4 x i32>* %srcLocal128, align 4
 ; DUMP:      ret void
 ; DUMP-NEXT: }