Add support to ValueTracking for determining that a pointer is non-null
by virtue of inbounds GEPs that preclude a null pointer.
This is a very common pattern in the code generated by std::vector and
other standard library routines which use allocators that test for null
pervasively. This is one step closer to teaching Clang+LLVM to be able
to produce an empty function for:
void f() {
std::vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
}
Which is related to getting them to completely fold SmallVector
push_back sequences into constants when inlining and other optimizations
make that a possibility.
llvm-svn: 169573
diff --git a/llvm/test/Transforms/InstSimplify/compare.ll b/llvm/test/Transforms/InstSimplify/compare.ll
index ce2bb79..56627b9 100644
--- a/llvm/test/Transforms/InstSimplify/compare.ll
+++ b/llvm/test/Transforms/InstSimplify/compare.ll
@@ -165,6 +165,46 @@
ret i1 %cmp
}
+define i1 @gep13(i8* %ptr) {
+; CHECK: @gep13
+; We can prove this GEP is non-null because it is inbounds.
+ %x = getelementptr inbounds i8* %ptr, i32 1
+ %cmp = icmp eq i8* %x, null
+ ret i1 %cmp
+; CHECK-NEXT: ret i1 false
+}
+
+define i1 @gep14({ {}, i8 }* %ptr) {
+; CHECK: @gep14
+; We can't simplify this because the offset of one in the GEP actually doesn't
+; move the pointer.
+ %x = getelementptr inbounds { {}, i8 }* %ptr, i32 0, i32 1
+ %cmp = icmp eq i8* %x, null
+ ret i1 %cmp
+; CHECK-NOT: ret i1 false
+}
+
+define i1 @gep15({ {}, [4 x {i8, i8}]}* %ptr, i32 %y) {
+; CHECK: @gep15
+; We can prove this GEP is non-null even though there is a user value, as we
+; would necessarily violate inbounds on one side or the other.
+ %x = getelementptr inbounds { {}, [4 x {i8, i8}]}* %ptr, i32 0, i32 1, i32 %y, i32 1
+ %cmp = icmp eq i8* %x, null
+ ret i1 %cmp
+; CHECK-NEXT: ret i1 false
+}
+
+define i1 @gep16(i8* %ptr, i32 %a) {
+; CHECK: @gep16
+; We can prove this GEP is non-null because it is inbounds and because we know
+; %b is non-zero even though we don't know its value.
+ %b = or i32 %a, 1
+ %x = getelementptr inbounds i8* %ptr, i32 %b
+ %cmp = icmp eq i8* %x, null
+ ret i1 %cmp
+; CHECK-NEXT: ret i1 false
+}
+
define i1 @zext(i32 %x) {
; CHECK: @zext
%e1 = zext i32 %x to i64