[IPSCCP] Don't require noundef for !range annotation

[nikic]

Summary

Since https://reviews.llvm.org/D141386 !range violations return poison instead of causing immediate undefined behavior. As such, it is fine for IPSCCP to infer !range even if the value might be poison. (The value cannot be undef as this would promote undef to poison, but this is already checked separately.)

This basically undoes the late change done to D83952, restoring it to its original version (which is now valid).

[nikic]

ping

[fhahn]

LGTM, thanks! The range is guaranteed to not include undef as per an earlier check.

[tingwang]

I saw following case failed due to this commit with IPSCCPPass opt -passes="ipsccp"

; ModuleID = 'ld-temp.o'
source_filename = "ld-temp.o"
target datalayout = "e-m:e-i64:64-n32:64-S128-v256:256:256-v512:512:512"
target triple = "powerpc64le-unknown-linux-gnu"

; Function Attrs: noinline nounwind optnone uwtable
define internal <2 x i64> @cntlzVector(<2 x i64> noundef %0) #0 {
  %2 = alloca <2 x i64>, align 16
  %3 = alloca <2 x i64>, align 16
  store <2 x i64> %0, ptr %3, align 16
  %4 = load <2 x i64>, ptr %3, align 16
  store <2 x i64> %4, ptr %2, align 16
  %5 = load <2 x i64>, ptr %2, align 16
  %6 = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> %5, i1 false)
  ret <2 x i64> %6
}

; Function Attrs: mustprogress nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare <2 x i64> @llvm.ctlz.v2i64(<2 x i64>, i1 immarg) #1

; Function Attrs: noinline nounwind optnone uwtable
define dso_local signext i32 @main() #0 {
  %1 = alloca i32, align 4
  %2 = alloca <2 x i64>, align 16
  store i32 0, ptr %1, align 4
  %3 = load <2 x i64>, ptr %2, align 16
  %4 = call <2 x i64> @cntlzVector(<2 x i64> noundef %3)
  store <2 x i64> %4, ptr %2, align 16
  ret i32 0
}

attributes #0 = { noinline nounwind optnone uwtable "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crbits,+crypto,+direct-move,+extdiv,+htm,+isa-v206-instructions,+isa-v207-instructions,+power8-vector,+vsx,-isa-v30-instructions,-power9-vector,-privileged,-quadword-atomics,-rop-protect,-spe" }
attributes #1 = { mustprogress nocallback nofree nosync nounwind speculatable willreturn }

!llvm.ident = !{!0}
!llvm.module.flags = !{!1, !2, !3, !4, !5, !6, !7, !8}

!0 = !{!""}
!1 = !{i32 1, !"wchar_size", i32 4}
!2 = !{i32 8, !"PIC Level", i32 2}
!3 = !{i32 7, !"PIE Level", i32 2}
!4 = !{i32 7, !"uwtable", i32 2}
!5 = !{i32 7, !"frame-pointer", i32 2}
!6 = !{i32 1, !"ThinLTO", i32 0}
!7 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
!8 = !{i32 1, !"LTOPostLink", i32 1}

[nikic]

@tingwang Thanks for the report. Here's a reduced test case:

define internal <2 x i64> @ctlz(<2 x i64> %arg) {
  %res = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> %arg, i1 false)
  ret <2 x i64> %res
}

define <2 x i64> @caller(<2 x i64> %arg) {
  %res = call <2 x i64> @ctlz(<2 x i64> %arg)
  ret <2 x i64> %res
}

declare <2 x i64> @llvm.ctlz.v2i64(<2 x i64>, i1)

The problem is that !range is currently not supported for vector types.

[nikic]

Fixed by https://github.com/llvm/llvm-project/commit/e0282cb4da9402de5712ac7855af6c71a03d0c19.

[DavidSpickett]

After this change one of our bots started failing a gcc test suite test on our SVE bot. However on closer inspection, it was that clang is now able to tail call some things it previously couldn't. Which is actually a good thing!

I've posted a fix for the test file https://reviews.llvm.org/D146143.