Description
Reproducer: https://godbolt.org/z/evTP9P17j
; bin/opt -passes=licm reduced.ll -S
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define void @_ZN25test7425_51072c957f3e023d3fn317hab8ab70cb1ea6b04E(ptr noalias writable align 2 dereferenceable(12) initializes((0, 12)) %0) {
%2 = alloca [56 x i8], align 8
%3 = getelementptr i8, ptr %0, i64 8
%4 = getelementptr i8, ptr %0, i64 10
br label %5
5: ; preds = %10, %1
%6 = getelementptr i8, ptr %2, i64 16
%7 = getelementptr i8, ptr %2, i64 16
store i16 0, ptr %3, align 2
store i16 0, ptr %4, align 2
%8 = load <4 x i32>, ptr %6, align 8
store <4 x i32> %8, ptr %7, align 8
br label %9
9: ; preds = %5
switch i8 1, label %11 [
i8 1, label %11
i8 0, label %10
]
10: ; preds = %9
store <4 x i16> zeroinitializer, ptr %0, align 2
br label %5
11: ; preds = %9, %9
ret void
}
define void @_ZN25test7425_51072c957f3e023d4main17hb2c14928af806df2E() {
%1 = alloca [64 x i8], align 8
call void @_ZN25test7425_51072c957f3e023d3fn317hab8ab70cb1ea6b04E(ptr %1)
ret void
}
After LICM, the first memory access to %0 is load <4 x i16>, ptr %0, align 1, which breaks the initializes attribute:
Initialization of memory means the first memory access is a non-volatile, non-atomic write.
The initializes attribute does not imply writeonly since initializes allows reading from the pointer after writing.
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define void @_ZN25test7425_51072c957f3e023d3fn317hab8ab70cb1ea6b04E(ptr noalias writable align 2 dereferenceable(12) initializes((0, 12)) %0) {
%2 = alloca [56 x i8], align 8
%3 = getelementptr i8, ptr %0, i64 8
%4 = getelementptr i8, ptr %0, i64 10
%5 = getelementptr i8, ptr %2, i64 16
%6 = getelementptr i8, ptr %2, i64 16
%.promoted = load <4 x i32>, ptr %5, align 8
%.promoted1 = load <4 x i16>, ptr %0, align 1
br label %7
7: ; preds = %11, %1
%8 = phi <4 x i16> [ zeroinitializer, %11 ], [ %.promoted1, %1 ]
%9 = phi <4 x i32> [ %9, %11 ], [ %.promoted, %1 ]
br label %10
10: ; preds = %7
switch i8 1, label %12 [
i8 1, label %12
i8 0, label %11
]
11: ; preds = %10
br label %7
12: ; preds = %10, %10
%.lcssa2 = phi <4 x i16> [ %8, %10 ], [ %8, %10 ]
%.lcssa = phi <4 x i32> [ %9, %10 ], [ %9, %10 ]
store i16 0, ptr %3, align 2
store i16 0, ptr %4, align 2
store <4 x i32> %.lcssa, ptr %5, align 8
store <4 x i16> %.lcssa2, ptr %0, align 1
ret void
}
Should we clarify the LangRef wording on initializes to allow loads before the initialization is complete, if they are not externally observable?
This case is generated by rustlantis + llubi.
Original rust mir program: https://gist.github.com/dtcxzyw/fcf0905a562f8734428e0b216198e0c0