FFI calls may create out-of-bounds loads #29988
Description
Given this Rust code:
#[repr(C)] struct S { f1: i32, f2: i32, f3: i32, } extern { fn foo(s: S); }A call to foo() generates IR like this on x86_64 Linux:
%S = type { i32, i32, i32 } ; ... %arg = alloca %S ; ... %2 = bitcast %S* %s to i8* %3 = bitcast %S* %arg to i8* call void @llvm.memcpy.p0i8.p0i8.i64(i8* %3, i8* %2, i64 12, i32 4, i1 false) %4 = bitcast %S* %arg to { i64, i64 }* %5 = load { i64, i64 }, { i64, i64 }* %4 call void @x({ i64, i64 } %5)So we have a 12 byte alloca from which we then read 16 bytes.