[clang] [llvm] [Clang] Add __builtin_assume_dereferenceable to encode deref assumption. (PR #121789)

[Johannes Doerfert via llvm-commits]

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@@ -0,0 +1,36 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+// CHECK-LABEL: @test1(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[A_ADDR:%.*]] = alloca ptr, align 8
+// CHECK-NEXT:    store ptr [[A:%.*]], ptr [[A_ADDR]], align 8
+// CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[A_ADDR]], align 8
+// CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0]], i64 10) ]
+// CHECK-NEXT:    call void @llvm.assume(i1 true) [ "nonnull"(ptr [[TMP0]]) ]
+// CHECK-NEXT:    [[TMP1:%.*]] = load ptr, ptr [[A_ADDR]], align 8
+// CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[TMP1]], i64 0
+// CHECK-NEXT:    [[TMP2:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+// CHECK-NEXT:    ret i32 [[TMP2]]
+//
+int test1(int *a) {
+  __builtin_assume_dereferenceable(a, 10);
+  return a[0];
+}
+
+// CHECK-LABEL: @test2(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[A_ADDR:%.*]] = alloca ptr, align 8
+// CHECK-NEXT:    store ptr [[A:%.*]], ptr [[A_ADDR]], align 8
+// CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[A_ADDR]], align 8
+// CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0]], i64 32) ]
+// CHECK-NEXT:    call void @llvm.assume(i1 true) [ "nonnull"(ptr [[TMP0]]) ]
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jdoerfert wrote:

Why two assumes and not one? I think later we'd merge them, maybe avoid the hassle.
Also, as mentioned in the other comment, we can't just do nonnull, we probably want a test for the non-nonnull case:
https://godbolt.org/z/1f3r8K9Pn
Note also the nonnull deduction.

https://github.com/llvm/llvm-project/pull/121789