[Attributor][MustExec] Deduce dereferenceable and nonnull attribute using MustBeExecutedContextExplorer

Summary:
In D65186 and related patches, MustBeExecutedContextExplorer is introduced. This enables us to traverse instructions guaranteed to execute from function entry. If we can know the argument is used as `dereferenceable` or `nonnull` in these instructions, we can mark `dereferenceable` or `nonnull` in the argument definition:

1. Memory instruction (similar to D64258)
Trace memory instruction pointer operand. Currently, only inbounds GEPs are traced.
```
define i64* @f(i64* %a) {
entry:
  %add.ptr = getelementptr inbounds i64, i64* %a, i64 1
; (because of inbounds GEP we can know that %a is at least dereferenceable(16))
  store i64 1, i64* %add.ptr, align 8
  ret i64* %add.ptr ; dereferenceable 8 (because above instruction stores into it)
}
```

2. Propagation from callsite (similar to D27855)
If `deref` or `nonnull` are known in call site parameter attributes we can also say that argument also that attribute.

```
declare void @use3(i8* %x, i8* %y, i8* %z);
declare void @use3nonnull(i8* nonnull %x, i8* nonnull %y, i8* nonnull %z);

define void @parent1(i8* %a, i8* %b, i8* %c) {
  call void @use3nonnull(i8* %b, i8* %c, i8* %a)
; Above instruction is always executed so we can say that@parent1(i8* nonnnull %a, i8* nonnull %b, i8* nonnull %c)
  call void @use3(i8* %c, i8* %a, i8* %b)
  ret void
}
```

Reviewers: jdoerfert, sstefan1, spatel, reames

Reviewed By: jdoerfert

Subscribers: xbolva00, hiraditya, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65402

llvm-svn: 374063

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/test/Transforms/FunctionAttrs/callbacks.ll b/llvm/test/Transforms/FunctionAttrs/callbacks.ll
index 3628bfa9daf..88fe0d037ca 100644
--- a/llvm/test/Transforms/FunctionAttrs/callbacks.ll
+++ b/llvm/test/Transforms/FunctionAttrs/callbacks.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -passes=attributor -aa-pipeline='basic-aa' -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=1 < %s | FileCheck %s
+; RUN: opt -S -passes=attributor -aa-pipeline='basic-aa' -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=2 < %s | FileCheck %s
 ; ModuleID = 'callback_simple.c'
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 
@@ -14,7 +14,7 @@ target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16
 ; FIXME: The callee -> call site direction is not working yet.
 
 define void @t0_caller(i32* %a) {
-; CHECK:       @t0_caller(i32* [[A:%.*]])
+; CHECK-LABEL: @t0_caller(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[B:%.*]] = alloca i32, align 32
 ; CHECK-NEXT:    [[C:%.*]] = alloca i32*, align 64
@@ -39,7 +39,7 @@ entry:
 ; Note that the first two arguments are provided by the callback_broker according to the callback in !1 below!
 ; The others are annotated with alignment information, amongst others, or even replaced by the constants passed to the call.
 define internal void @t0_callback_callee(i32* %is_not_null, i32* %ptr, i32* %a, i64 %b, i32** %c) {
-; CHECK:       @t0_callback_callee(i32* nocapture writeonly [[IS_NOT_NULL:%.*]], i32* nocapture readonly [[PTR:%.*]], i32* [[A:%.*]], i64 [[B:%.*]], i32** nocapture nonnull readonly align 64 dereferenceable(8) [[C:%.*]])
+; CHECK-LABEL: @t0_callback_callee(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[PTR_VAL:%.*]] = load i32, i32* [[PTR:%.*]], align 8
 ; CHECK-NEXT:    store i32 [[PTR_VAL]], i32* [[IS_NOT_NULL:%.*]]