[llvm] [ConstraintElim] Drop invalid rows instead of failing the elimination (PR #76299)

[Florian Hahn via llvm-commits]

================
@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -passes=constraint-elimination -S %s | FileCheck %s
+
+define void @f(i64 %a3, i64 %numElements) {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: i64 [[A3:%.*]], i64 [[NUMELEMENTS:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[COND:%.*]] = icmp ule i64 [[NUMELEMENTS]], 1152921504606846975
+; CHECK-NEXT:    call void @llvm.assume(i1 [[COND]])
+; CHECK-NEXT:    [[A1:%.*]] = shl nuw i64 [[NUMELEMENTS]], 4
+; CHECK-NEXT:    br label [[IF_END:%.*]]
+; CHECK:       if.end:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i64 [[A1]], [[A3]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_END_I:%.*]], label [[ABORT:%.*]]
+; CHECK:       if.end.i:
+; CHECK-NEXT:    [[CMP2_NOT_I:%.*]] = icmp ult i64 [[A1]], [[A3]]
+; CHECK-NEXT:    br i1 [[CMP2_NOT_I]], label [[ABORT]], label [[EXIT:%.*]]
+; CHECK:       abort:
+; CHECK-NEXT:    tail call void @llvm.trap()
+; CHECK-NEXT:    unreachable
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %cond = icmp ule i64 %numElements, 1152921504606846975
+  call void @llvm.assume(i1 %cond)
+  %a1 = shl nuw i64 %numElements, 4
+  br label %if.end
+if.end:
+  %cmp = icmp ugt i64 %a1, %a3
+  br i1 %cmp, label %if.end.i, label %abort
+if.end.i:
+  %cmp2.not.i = icmp ult i64 %a1, %a3
+  br i1 %cmp2.not.i, label %abort, label %exit
+abort:
+  tail call void @llvm.trap()
----------------
fhahn wrote:

might be better to change the function to return different values on the different exit paths to make verification simpler.

https://github.com/llvm/llvm-project/pull/76299