[GuardWidening][Test] Illustrate incorrect insertion point case

[aleksandr.popov]

Summary

Add test case when we widen condition to the branch which was previously
widened itself. We turn this branch from loop-invariant into loop-variant
one and cause issue similar to
https://github.com/llvm/llvm-project/issues/60234

llvm/test/Transforms/GuardWidening/eliminated-branch-not-insert-point.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -S -passes=guard-widening < %s | FileCheck %s
+
+; TODO: Fix incorrect insertion point
+; - firstly we widen 'br i1 %exiplicit_guard_cond1' into 'br i1 %wc0'
+; and turn it into 'br i1 true';
+; - then we widen 'br i1 %exiplicit_guard_cond2' into 'br i1 true',
+; which is still considered as a guard;
+; - thus 'br i1 true' becomes an insertion point for the condition
+; and it's incorrect because we turn loop invariant branch into loop
+; variant one.
+define i64 @test(ptr addrspace(1) %0, i64 %1, i32 %2) {
+; CHECK-LABEL: define i64 @test
+; CHECK-SAME: (ptr addrspace(1) [[TMP0:%.*]], i64 [[TMP1:%.*]], i32 [[TMP2:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[DOTGW_FR:%.*]] = freeze i32 [[TMP2]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[DOTGW_FR]], 0
+; CHECK-NEXT:    [[WIDE_CHK:%.*]] = and i1 true, [[CMP]]
+; CHECK-NEXT:    [[WC0:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[TMP3:%.*]] = and i1 [[WIDE_CHK]], [[WC0]]
+; CHECK-NEXT:    br i1 [[TMP3]], label [[PREHEADER:%.*]], label [[DEOPT:%.*]]
+; CHECK:       preheader:
+; CHECK-NEXT:    [[WC1:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND1:%.*]] = and i1 [[CMP]], [[WC1]]
+; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
+; CHECK:       loop.header:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[IV_NEXT:%.*]], [[LOOP_BODY:%.*]] ]
+; CHECK-NEXT:    [[CMP_IV:%.*]] = icmp ult i32 [[IV]], 100
+; CHECK-NEXT:    [[WIDE_CHK1:%.*]] = and i1 true, [[CMP_IV]]
+; CHECK-NEXT:    br i1 [[WIDE_CHK1]], label [[LOOP_BODY]], label [[DEOPT]]
+; CHECK:       loop.body:
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[WC2:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND2:%.*]] = and i1 [[CMP_IV]], [[WC2]]
+; CHECK-NEXT:    br i1 true, label [[LOOP_HEADER]], label [[DEOPT]]
+; CHECK:       deopt:
+; CHECK-NEXT:    [[DEOPTCALL:%.*]] = call i64 (...) @llvm.experimental.deoptimize.i64() [ "deopt"() ]
+; CHECK-NEXT:    ret i64 [[DEOPTCALL]]
+;
+entry:
+  %wc0 = call i1 @llvm.experimental.widenable.condition()
+  br i1 %wc0, label %preheader, label %deopt
+
+preheader:
+  %cmp = icmp eq i32 %2, 0
+  %wc1 = call i1 @llvm.experimental.widenable.condition()
+  %exiplicit_guard_cond1 = and i1 %cmp, %wc1
+  br label %loop.header
+
+loop.header:
+  %iv = phi i32 [ 0, %preheader ], [ %iv.next, %loop.body ]
+  br i1 %exiplicit_guard_cond1, label %loop.body, label %deopt
+
+loop.body:
+  %iv.next = add nuw nsw i32 %iv, 1
+  %cmp.iv = icmp ult i32 %iv, 100
+  %wc2 = call i1 @llvm.experimental.widenable.condition()
+  %exiplicit_guard_cond2 = and i1 %cmp.iv, %wc2
+  br i1 %exiplicit_guard_cond2, label %loop.header, label %deopt
+
+deopt:
+  %deoptcall = call i64 (...) @llvm.experimental.deoptimize.i64() [ "deopt"() ]
+  ret i64 %deoptcall
+}
+
+declare i1 @llvm.experimental.widenable.condition()
+declare i64 @llvm.experimental.deoptimize.i64(...)