[IRCE] Add tests for conservative bound check

Prevent cases in which the start value of IV is bigger than bound for
increasing.

Prevent cases in which the start value of IV is smaller than bound for
decreasing.

Differential Revision: https://reviews.llvm.org/D101174

Author: jaykang10

llvm/test/Transforms/IRCE/variable-loop-bounds.ll

@@ -9,6 +9,8 @@
 ; CHECK: irce: in function signed_var_imm_dec_sge: constrained Loop at depth 1 containing: %for.body<header>,%if.else,%for.inc<latch><exiting>
 ; CHECK: irce: in function signed_var_imm_dec_ne: constrained Loop at depth 1 containing: %for.body<header>,%if.else,%for.inc<latch><exiting>
 ; CHECK-NOT: irce: in function signed_var_imm_dec_eq: constrained Loop at depth 1 containing: %for.body<header>,%if.else,%for.inc<latch><exiting>
+; CHECK-NOT: irce: in function test_dec_bound_with_smaller_start_than_bound: constrained Loop at depth 1 containing: %for.body<header>,%if.else,%for.dec<latch><exiting>
+; CHECK-NOT: irce: in function test_inc_bound_with_bigger_start_than_bound: constrained Loop at depth 1 containing: %for.body<header>,%if.else,%for.dec<latch><exiting>
 
 ; CHECK-LABEL: test_inc_eq(
 ; CHECK: main.exit.selector:
@@ -352,3 +354,49 @@ for.inc:                                          ; preds = %for.body, %if.else
   %cmp = icmp eq i32 %dec, %M
   br i1 %cmp, label %for.cond.cleanup, label %for.body
 }
+
+; CHECK-LABEL: @test_dec_bound_with_smaller_start_than_bound(
+; CHECK-NOT:       preloop.exit.selector:
+define void @test_dec_bound_with_smaller_start_than_bound(i64 %0) {
+entry:
+  br label %for.body
+
+for.body:                                                ; preds = %for.dec, %entry
+  %iv = phi i64 [ %dec, %for.dec ], [ 0, %entry ]
+  %1 = icmp slt i64 %iv, %0
+  br i1 %1, label %if.else, label %for.dec
+
+if.else:                                                ; preds = %for.body
+  br label %for.dec
+
+for.dec:                                                ; preds = %if.else, %for.body
+  %dec = sub nuw nsw i64 %iv, 1
+  %2 = icmp slt i64 %dec, 1
+  br i1 %2, label %exit, label %for.body
+
+exit:                                               ; preds = %for.dec
+  ret void
+}
+
+; CHECK-LABEL: @test_inc_bound_with_bigger_start_than_bound(
+; CHECK-NOT:       main.exit.selector:
+define void @test_inc_bound_with_bigger_start_than_bound(i32 %0) {
+entry:
+  br label %for.body
+
+for.body:                                                ; preds = %for.inc, %entry
+  %iv = phi i32 [ %inc, %for.inc ], [ 200, %entry ]
+  %1 = icmp slt i32 %iv, %0
+  br i1 %1, label %if.else, label %for.inc
+
+if.else:                                                ; preds = %for.body
+  br label %for.inc
+
+for.inc:                                                ; preds = %if.else, %for.body
+  %inc = add nsw i32 %iv, 1
+  %2 = icmp sgt i32 %inc, 100
+  br i1 %2, label %exit, label %for.body
+
+exit:                                                ; preds = %for.inc
+  ret void
+}