[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, 44 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InferFunctionAttrs/dereferenceable.ll b/llvm/test/Transforms/InferFunctionAttrs/dereferenceable.ll
index f6580826bd1..17c76f11d6c 100644
--- a/llvm/test/Transforms/InferFunctionAttrs/dereferenceable.ll
+++ b/llvm/test/Transforms/InferFunctionAttrs/dereferenceable.ll
@@ -1,10 +1,17 @@
 ; RUN: opt < %s -inferattrs -S | FileCheck %s
+; RUN: opt < %s -attributor --attributor-disable=false -S | FileCheck %s --check-prefix=ATTRIBUTOR
+
+
 
 ; Determine dereference-ability before unused loads get deleted:
 ; https://bugs.llvm.org/show_bug.cgi?id=21780
 
 define <4 x double> @PR21780(double* %ptr) {
 ; CHECK-LABEL: @PR21780(double* %ptr)
+; FIXME: this should be @PR21780(double* nonnull dereferenceable(32) %ptr) 
+;        trakcing use of GEP in Attributor would fix this problem.
+; ATTRIBUTOR-LABEL: @PR21780(double* nocapture nonnull readonly dereferenceable(8) %ptr)
+
   ; GEP of index 0 is simplified away.
   %arrayidx1 = getelementptr inbounds double, double* %ptr, i64 1
   %arrayidx2 = getelementptr inbounds double, double* %ptr, i64 2
@@ -23,6 +30,43 @@ define <4 x double> @PR21780(double* %ptr) {
   ret <4 x double> %shuffle
 }
 
+
+define double @PR21780_only_access3_with_inbounds(double* %ptr) {
+; CHECK-LABEL: @PR21780_only_access3_with_inbounds(double* %ptr)
+; FIXME: this should be @PR21780_only_access3_with_inbounds(double* nonnull dereferenceable(32) %ptr)
+;        trakcing use of GEP in Attributor would fix this problem.
+; ATTRIBUTOR-LABEL: @PR21780_only_access3_with_inbounds(double* nocapture readonly %ptr) 
+
+  %arrayidx3 = getelementptr inbounds double, double* %ptr, i64 3
+  %t3 = load double, double* %arrayidx3, align 8
+  ret double %t3
+}
+
+define double @PR21780_only_access3_without_inbounds(double* %ptr) {
+; CHECK-LABEL: @PR21780_only_access3_without_inbounds(double* %ptr)
+; ATTRIBUTOR-LABEL: @PR21780_only_access3_without_inbounds(double* nocapture readonly %ptr)
+  %arrayidx3 = getelementptr double, double* %ptr, i64 3
+  %t3 = load double, double* %arrayidx3, align 8
+  ret double %t3
+}
+
+define double @PR21780_without_inbounds(double* %ptr) {
+; CHECK-LABEL: @PR21780_without_inbounds(double* %ptr)
+; FIXME: this should be @PR21780_without_inbounds(double* nonnull dereferenceable(32) %ptr)
+; ATTRIBUTOR-LABEL: @PR21780_without_inbounds(double* nocapture nonnull readonly dereferenceable(8) %ptr)
+
+  %arrayidx1 = getelementptr double, double* %ptr, i64 1
+  %arrayidx2 = getelementptr double, double* %ptr, i64 2
+  %arrayidx3 = getelementptr double, double* %ptr, i64 3
+
+  %t0 = load double, double* %ptr, align 8
+  %t1 = load double, double* %arrayidx1, align 8
+  %t2 = load double, double* %arrayidx2, align 8
+  %t3 = load double, double* %arrayidx3, align 8
+
+  ret double %t3
+}
+
 ; Unsimplified, but still valid. Also, throw in some bogus arguments.
 
 define void @gep0(i8* %unused, i8* %other, i8* %ptr) {