patrick-rivos
commented
4 months ago Partially cleaned up testcase:
target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
target triple = "riscv64-unknown-linux-gnu"
define i32 @main() #0 {
entry:
%sext.0 = sext i16 0 to i32
br label %loop.preheader
loop.preheader: ; preds = %loop.preheader, %entry
%iv.i = phi i64 [ %iv.next.i, %loop.preheader ], [ 0, %entry ]
%phi.0 = phi i8 [ %or.0, %loop.preheader ], [ 0, %entry ]
%max.0 = tail call i32 @llvm.smax.i32(i32 0, i32 %sext.0)
%cmp = icmp eq i32 %max.0, 0
%zext.true = zext i1 %cmp to i32
%0 = lshr i32 %zext.true, 1
%1 = trunc i32 %0 to i8
%or.0 = or i8 %phi.0, %1
%iv.next.i = add i64 %iv.i, 1
%cmp.us.i = icmp slt i64 %iv.i, 1
br i1 %cmp.us.i, label %loop.preheader, label %loop.exit
loop.exit: ; preds = %loop.preheader
store i8 %or.0, ptr null, align 1
ret i32 0
}
; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare i32 @llvm.smax.i32(i32, i32) #1
attributes #0 = { "target-features"="+64bit,+v" }Basic analysis:
The issue is caused by:
https://github.com/llvm/llvm-project/blob/39bfdb7f33f7f53ab662c5cea25129c45a9b4c11/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp#L1074-L1076
when %sext.0 = sext i16 0 to i32 is the only unaccounted for MinBWs entry.
Op->getLiveInIRValue() returns a Constant i32 0, so the dynamic cast to Instruction returns a null pointer which does not exist in MinBWs.
I think the Constant is an optimized sext i16 0 to i32 so I'll try to find where the constant comes from next.
Reduced LLVM IR:
Backtrace:
Godbolt: https://godbolt.org/z/6TxWGMz6e
Assert: https://github.com/llvm/llvm-project/blob/c403a478076a16172d9b50e16c288b0d360f42ce/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp#L1061-L1063
Found via fuzzer.