[DAG] SelectionDAG::canCreateUndefOrPoison - add ISD::SCMP/UCMP handling + tests

[Temperz87]

This pr aims to resolve #152144
In SelectionDAG::canCreateUndefOrPoison the ISD::SCMP/UCMP cases are added to always return false as they cannot generate poison or undef
The freeze-binary.ll file is now testing the SCMP/UCMP cases

[github-actions]

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

[llvmbot]

@llvm/pr-subscribers-llvm-selectiondag

@llvm/pr-subscribers-backend-x86

Author: None (Temperz87)

Changes

This pr aims to resolve #152144
In SelectionDAG::canCreateUndefOrPoison the ISD::SCMP/UCMP cases are added to always return false as they cannot generate poison or undef
The freeze-binary.ll file is now testing the SCMP/UCMP cases

---

Full diff: https://github.com/llvm/llvm-project/pull/154127.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (+2)
• (modified) llvm/test/CodeGen/X86/freeze-binary.ll (+72-1)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 84282d8a1c37b..cbbf885115a59 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5748,6 +5748,8 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::FMA:
   case ISD::FMAD:
   case ISD::FP_EXTEND:
+  case ISD::SCMP:
+  case ISD::UCMP:
     // No poison except from flags (which is handled above)
     return false;
 
diff --git a/llvm/test/CodeGen/X86/freeze-binary.ll b/llvm/test/CodeGen/X86/freeze-binary.ll
index 962ffe47d0d51..af5b26f6e2dd9 100644
--- a/llvm/test/CodeGen/X86/freeze-binary.ll
+++ b/llvm/test/CodeGen/X86/freeze-binary.ll
@@ -924,6 +924,77 @@ define i32 @freeze_usubo(i32 %a0, i32 %a1, i8 %a2, i8 %a3) nounwind {
   ret i32 %r
 }
 
+
+define i32 @freeze_scmp(i32 %a0) nounwind {
+; X86-LABEL: freeze_scmp:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    cmpl $2, %eax
+; X86-NEXT:    setl %al
+; X86-NEXT:    setg %cl
+; X86-NEXT:    subb %al, %cl
+; X86-NEXT:    movsbl %cl, %eax
+; X86-NEXT:    cmpl $2, %eax
+; X86-NEXT:    setl %al
+; X86-NEXT:    setg %cl
+; X86-NEXT:    subb %al, %cl
+; X86-NEXT:    movsbl %cl, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: freeze_scmp:
+; X64:       # %bb.0:
+; X64-NEXT:    cmpl $2, %edi
+; X64-NEXT:    setl %al
+; X64-NEXT:    setg %cl
+; X64-NEXT:    subb %al, %cl
+; X64-NEXT:    movsbl %cl, %eax
+; X64-NEXT:    cmpl $2, %eax
+; X64-NEXT:    setl %al
+; X64-NEXT:    setg %cl
+; X64-NEXT:    subb %al, %cl
+; X64-NEXT:    movsbl %cl, %eax
+; X64-NEXT:    retq
+  %x = call i32 @llvm.scmp.i32(i32 %a0, i32 2)
+  %y = freeze i32 %x
+  %z = call i32 @llvm.scmp.i32(i32 %y, i32 2)
+  ret i32 %z
+}
+
+define i32 @freeze_ucmp(i32 %a0) nounwind {
+; X86-LABEL: freeze_ucmp:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    cmpl $3, %eax
+; X86-NEXT:    setae %cl
+; X86-NEXT:    cmpl $2, %eax
+; X86-NEXT:    sbbb $0, %cl
+; X86-NEXT:    movsbl %cl, %eax
+; X86-NEXT:    cmpl $3, %eax
+; X86-NEXT:    setae %cl
+; X86-NEXT:    cmpl $2, %eax
+; X86-NEXT:    sbbb $0, %cl
+; X86-NEXT:    movsbl %cl, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: freeze_ucmp:
+; X64:       # %bb.0:
+; X64-NEXT:    cmpl $3, %edi
+; X64-NEXT:    setae %al
+; X64-NEXT:    cmpl $2, %edi
+; X64-NEXT:    sbbb $0, %al
+; X64-NEXT:    movsbl %al, %eax
+; X64-NEXT:    cmpl $3, %eax
+; X64-NEXT:    setae %cl
+; X64-NEXT:    cmpl $2, %eax
+; X64-NEXT:    sbbb $0, %cl
+; X64-NEXT:    movsbl %cl, %eax
+; X64-NEXT:    retq
+  %x = call i32 @llvm.ucmp.i32(i32 %a0, i32 2)
+  %y = freeze i32 %x
+  %z = call i32 @llvm.ucmp.i32(i32 %y, i32 2)
+  ret i32 %z
+}
+
 define void @pr59676_frozen(ptr %dst, i32 %x.orig) {
 ; X86-LABEL: pr59676_frozen:
 ; X86:       # %bb.0:
@@ -1036,4 +1107,4 @@ define void @pr59676_nsw(ptr %dst, i32 %x) {
   %div = sdiv i32 %area, 42
   store i32 %div, ptr %dst, align 4
   ret void
-}
+}
\ No newline at end of file

[Temperz87]

Paging @RKSimon for review, thank you in advance!

[RKSimon]

does this actually work?

[Temperz87]

I think so? The local tests are passing and I don't see why it shouldn't be working

[Temperz87]

i realized that the test was always returning -1 so I've made it not do that in the event that it can get folded

[RKSimon]

does this actually work?

[Temperz87]

I've changed this test case so that 0 is in the range of possible outputs

[Temperz87]

Can you add it in the same category as umax amd umin in ir and globalisel too since we are here already?

Is the same change that RKSimon suggested?

[github-actions]

@Temperz87 Congratulations on having your first Pull Request (PR) merged into the LLVM Project!

Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR.

Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues.

How to do this, and the rest of the post-merge process, is covered in detail here.

If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again.

If you don't get any reports, no action is required from you. Your changes are working as expected, well done!