[Attributor] Deal with shrinking dereferenceability in a loop
Summary:
If we have a loop in which the dereferenceability of a pointer decreases
we did slowly decrease it iteration by iteration, leading to a timeout.
With this patch we detect such circular reasoning and indicate a
fixpoint early.
Reviewers: uenoku, sstefan1
Subscribers: hiraditya, bollu, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66558
llvm-svn: 369784
diff --git a/llvm/test/Transforms/FunctionAttrs/dereferenceable.ll b/llvm/test/Transforms/FunctionAttrs/dereferenceable.ll
index f61b62e..3ed32d3 100644
--- a/llvm/test/Transforms/FunctionAttrs/dereferenceable.ll
+++ b/llvm/test/Transforms/FunctionAttrs/dereferenceable.ll
@@ -1,6 +1,8 @@
; RUN: opt -attributor --attributor-disable=false -attributor-max-iterations=4 -S < %s | FileCheck %s --check-prefixes=ATTRIBUTOR
+declare void @deref_phi_user(i32* %a);
+
; TEST 1
; take mininimum of return values
;
@@ -52,8 +54,7 @@
; TEST 5
; loop in which dereferenceabily "grows"
-declare void @deref_phi_user(i32* %a);
-define void @deref_phi(i32* dereferenceable(4000) %a) {
+define void @deref_phi_growing(i32* dereferenceable(4000) %a) {
entry:
br label %for.cond
@@ -80,3 +81,33 @@
for.end: ; preds = %for.cond.cleanup
ret void
}
+
+; TEST 6
+; loop in which dereferenceabily "shrinks"
+define void @deref_phi_shrinking(i32* dereferenceable(4000) %a) {
+entry:
+ br label %for.cond
+
+for.cond: ; preds = %for.inc, %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+ %a.addr.0 = phi i32* [ %a, %entry ], [ %incdec.ptr, %for.inc ]
+; CHECK: call void @deref_phi_user(i32* %a.addr.0)
+ call void @deref_phi_user(i32* %a.addr.0)
+ %tmp = load i32, i32* %a.addr.0, align 4
+ %cmp = icmp slt i32 %i.0, %tmp
+ br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup: ; preds = %for.cond
+ br label %for.end
+
+for.body: ; preds = %for.cond
+ br label %for.inc
+
+for.inc: ; preds = %for.body
+ %incdec.ptr = getelementptr inbounds i32, i32* %a.addr.0, i64 1
+ %inc = add nuw nsw i32 %i.0, 1
+ br label %for.cond
+
+for.end: ; preds = %for.cond.cleanup
+ ret void
+}