Subzero: Elide checks of known valid accesses of locals

tests_lit/asan_tests/instrumentload.ll

Index: tests_lit/asan_tests/instrumentload.ll
diff --git a/tests_lit/asan_tests/instrumentload.ll b/tests_lit/asan_tests/instrumentload.ll
index 811e6232751962cd993fb15d983b918207f9414f..753984dfb4dc1ec5a1d6c4f81d8d19d6a7adb39c 100644
--- a/tests_lit/asan_tests/instrumentload.ll
+++ b/tests_lit/asan_tests/instrumentload.ll
@@ -20,12 +20,9 @@
 @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*
@@ -39,12 +36,6 @@ define internal void @doLoads() {
   %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
@@ -57,19 +48,19 @@ define internal void @doLoads() {
   %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