[Attributor] Track a GEP Instruction in align deduction

Summary:
This patch enables us to track GEP instruction in align deduction.
If a pointer `B` is defined as `A+Offset` and known to have alignment `C`, there exists some integer Q such that
```
 A + Offset = C * Q = B
```
 So we can say that the maximum power of two which is a divisor of gcd(Offset, C) is an alignment.

Reviewers: jdoerfert, sstefan1

Reviewed By: jdoerfert

Subscribers: lebedev.ri, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70392

3 files changed, 63 insertions, 3 deletions

diff --git a/llvm/test/Transforms/FunctionAttrs/align.ll b/llvm/test/Transforms/FunctionAttrs/align.ll
index da7bd1b5cc9..b8817a44fce 100644
--- a/llvm/test/Transforms/FunctionAttrs/align.ll
+++ b/llvm/test/Transforms/FunctionAttrs/align.ll
@@ -337,5 +337,66 @@ define i64 @test11(i32* %p) {
   %ret = load i64, i64* %p-cast, align 8
   ret i64 %ret
 }
+
+; TEST 12
+; Test for deduction using must-be-executed-context and GEP instruction 
+
+; FXIME: %p should have nonnull
+; ATTRIBUTOR: define i64 @test12-1(i32* nocapture nofree readonly align 16 %p)
+define i64 @test12-1(i32* align 4 %p) {
+  %p-cast = bitcast i32* %p to i64*
+  %arrayidx0 = getelementptr i64, i64* %p-cast, i64 1
+  %arrayidx1 = getelementptr i64, i64* %arrayidx0, i64 3
+  %ret = load i64, i64* %arrayidx1, align 16
+  ret i64 %ret
+}
+
+; FXIME: %p should have nonnull
+; ATTRIBUTOR: define i64 @test12-2(i32* nocapture nofree readonly align 16 %p)
+define i64 @test12-2(i32* align 4 %p) {
+  %p-cast = bitcast i32* %p to i64*
+  %arrayidx0 = getelementptr i64, i64* %p-cast, i64 0
+  %ret = load i64, i64* %arrayidx0, align 16
+  ret i64 %ret
+}
+
+; FXIME: %p should have nonnull
+; ATTRIBUTOR: define void @test12-3(i32* nocapture nofree writeonly align 16 %p)
+define void @test12-3(i32* align 4 %p) {
+  %p-cast = bitcast i32* %p to i64*
+  %arrayidx0 = getelementptr i64, i64* %p-cast, i64 1
+  %arrayidx1 = getelementptr i64, i64* %arrayidx0, i64 3
+  store i64 0, i64* %arrayidx1, align 16
+  ret void 
+}
+
+; FXIME: %p should have nonnull
+; ATTRIBUTOR: define void @test12-4(i32* nocapture nofree writeonly align 16 %p)
+define void @test12-4(i32* align 4 %p) {
+  %p-cast = bitcast i32* %p to i64*
+  %arrayidx0 = getelementptr i64, i64* %p-cast, i64 0
+  store i64 0, i64* %arrayidx0, align 16
+  ret void 
+}
+
+declare void @use(i64*) willreturn nounwind
+
+; ATTRIBUTOR: define void @test12-5(i32* align 16 %p)
+define void @test12-5(i32* align 4 %p) {
+  %p-cast = bitcast i32* %p to i64*
+  %arrayidx0 = getelementptr i64, i64* %p-cast, i64 1
+  %arrayidx1 = getelementptr i64, i64* %arrayidx0, i64 3
+  tail call void @use(i64* align 16 %arrayidx1)
+  ret void 
+}
+
+; ATTRIBUTOR: define void @test12-6(i32* align 16 %p)
+define void @test12-6(i32* align 4 %p) {
+  %p-cast = bitcast i32* %p to i64*
+  %arrayidx0 = getelementptr i64, i64* %p-cast, i64 0
+  tail call void @use(i64* align 16 %arrayidx0)
+  ret void 
+}
+
 attributes #0 = { nounwind uwtable noinline }
 attributes #1 = { uwtable noinline }
diff --git a/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll b/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
index fa4d984e931..79075268ed4 100644
--- a/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
+++ b/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
@@ -260,8 +260,7 @@ entry:
 ; }
 ;
 ; There should *not* be a no-capture attribute on %a
-; FIXME: %a should have align 8
-; CHECK: define nonnull align 8 dereferenceable(8) i64* @not_captured_but_returned_1(i64* nofree nonnull writeonly dereferenceable(16) "no-capture-maybe-returned" %a)
+; CHECK: define nonnull align 8 dereferenceable(8) i64* @not_captured_but_returned_1(i64* nofree nonnull writeonly align 8 dereferenceable(16) "no-capture-maybe-returned" %a)
 define i64* @not_captured_but_returned_1(i64* %a) #0 {
 entry:
   %add.ptr = getelementptr inbounds i64, i64* %a, i64 1
diff --git a/llvm/test/Transforms/FunctionAttrs/nocapture.ll b/llvm/test/Transforms/FunctionAttrs/nocapture.ll
index c54559883ae..a78af104167 100644
--- a/llvm/test/Transforms/FunctionAttrs/nocapture.ll
+++ b/llvm/test/Transforms/FunctionAttrs/nocapture.ll
@@ -259,7 +259,7 @@ define void @test_atomicrmw(i32* %p) {
 }
 
 ; FNATTR: define void @test_volatile(i32* %x)
-; ATTRIBUTOR: define void @test_volatile(i32* nofree %x)
+; ATTRIBUTOR: define void @test_volatile(i32* nofree align 4 %x)
 define void @test_volatile(i32* %x) {
 entry:
   %gep = getelementptr i32, i32* %x, i64 1