lebedev.ri added a comment.
Release notes missing.
I think the canonical way to silence it (via masking?) should be at least
mentioned.
================
Comment at: clang/lib/CodeGen/CGExprScalar.cpp:3872-3884
llvm::Value *BitsShiftedOff = Builder.CreateLShr(
Ops.LHS, Builder.CreateSub(PromotedWidthMinusOne, RHS, "shl.zeros",
/*NUW*/ true, /*NSW*/ true),
"shl.check");
- if (CGF.getLangOpts().CPlusPlus) {
+ if (SanitizeUnsignedBase || CGF.getLangOpts().CPlusPlus) {
// In C99, we are not permitted to shift a 1 bit into the sign bit.
// Under C++11's rules, shifting a 1 bit into the sign bit is
----------------
Why is this so complicated? Shouldn't this just be:
https://alive2.llvm.org/ce/z/scTqfX
```
$ /repositories/alive2/build-Clang-release/alive-tv /tmp/test.ll
--smt-to=100000 --disable-undef-input
----------------------------------------
@2 = global 32 bytes, align 16
define i32 @src(i32 %arg, i32 %arg1) {
%bb:
%i = icmp ugt i32 %arg1, 31
%i2 = sub nsw nuw i32 31, %arg1 ; NOPE
%i3 = lshr i32 %arg, %i2 ; NOPE
%i4 = icmp ult i32 %i3, 2 ; NOPE
%i5 = or i1 %i, %i4
br i1 %i5, label %bb9, label %bb6
%bb6:
%i7 = zext i32 %arg to i64
%i8 = zext i32 %arg1 to i64
%__constexpr_0 = bitcast * @2 to *
call void @__ubsan_handle_shift_out_of_bounds(* %__constexpr_0, i64 %i7, i64
%i8)
br label %bb9
%bb9:
%i10 = shl i32 %arg, %arg1
ret i32 %i10
}
=>
@2 = global 32 bytes, align 16
define i32 @tgt(i32 %arg, i32 %arg1) {
%bb:
%i = icmp ugt i32 %arg1, 31
%iZZ0 = shl i32 %arg, %arg1 ; HI!
%iZZ1 = lshr i32 %iZZ0, %arg1 ; OVER HERE
%i4 = icmp eq i32 %arg, %iZZ1 ; LOOK!
%i5 = or i1 %i, %i4
br i1 %i5, label %bb9, label %bb6
%bb6:
%i7 = zext i32 %arg to i64
%i8 = zext i32 %arg1 to i64
%__constexpr_0 = bitcast * @2 to *
call void @__ubsan_handle_shift_out_of_bounds(* %__constexpr_0, i64 %i7, i64
%i8)
br label %bb9
%bb9:
ret i32 %iZZ0
}
Transformation seems to be correct!
```
which will then be migrated to use `@llvm.ushl.with.overflow` once it's there.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D86000/new/
https://reviews.llvm.org/D86000
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