Add a more meaningful check to make sure we are not merging blocks (#4186)

This is a follow-up to
#4176 (comment)

I am now counting the number of blocks with (17) and without (31) block
merging. I double checked to make sure this does not pass when we use an
aggressive region simplification strategy.

Author: giuseros

test/Conversion/amd/amd-convert-builtin-func.mlir

@@ -2,6 +2,7 @@
 
 // Trying to merge those blocks will cause a lot of duplication in the block arguments, which will cause
 // an exponential growth of the argument length. Make sure we don't try to merge those blocks.
+// CHECK-COUNT-7: ^bb{{[0-9]+}}:
 module {
   llvm.func @rand() -> i1
   llvm.func @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(!llvm.ptr<1>, i32, i1) attributes {libname = "", libpath = ""}
@@ -11,53 +12,16 @@ module {
     %10 = llvm.icmp "eq" %arg0, %0 : i64
     %true = llvm.mlir.constant(1 : i1) : i1
     %c = llvm.mlir.constant(1 : i32) : i32
-    // CHECK: llvm.cond_br {{.*}}, ^bb{{.*}}, ^bb{{.*}}
-    llvm.cond_br %10, ^bb1, ^bb14
+    llvm.cond_br %10, ^bb1, ^bb2
   ^bb1:  // pred: ^bb0
-    %11 = llvm.call @rand() : () -> i1
-    // CHECK: llvm.cond_br {{.*}}, ^bb{{.*}}, ^bb{{.*}}
-    llvm.cond_br %11, ^bb2, ^bb3
-  ^bb2:  // pred: ^bb1
     llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%1, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb4
-  ^bb3:  // pred: ^bb1
-    llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%2, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb4
-  ^bb4:  // 2 preds: ^bb2, ^bb3
-    %14 = llvm.call @rand() : () -> i1
-    // CHECK: llvm.cond_br {{.*}}, ^bb{{.*}}, ^bb{{.*}}
-    llvm.cond_br %14, ^bb5, ^bb6
-  ^bb5:  // pred: ^bb4
-    llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%3, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb13
-  ^bb6:  // pred: ^bb4
-    llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%4, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb13
-  ^bb13:  // 2 preds: ^bb11, ^bb12
-    llvm.br ^bb27
-  ^bb14:  // pred: ^bb0
-    %23 = llvm.call @rand() : () -> i1
-    // CHECK: llvm.cond_br {{.*}}, ^bb{{.*}}, ^bb{{.*}}
-    llvm.cond_br %23, ^bb15, ^bb16
-  ^bb15:  // pred: ^bb14
+    llvm.br ^bb3
+
+  ^bb2:  // pred: ^bb0
     llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%4, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb17
-  ^bb16:  // pred: ^bb14
-    llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%3, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb17
-  ^bb17:  // 2 preds: ^bb15, ^bb16
-    %26 = llvm.call @rand() : () -> i1
-    // CHECK: llvm.cond_br {{.*}}, ^bb{{.*}}, ^bb{{.*}}
-    llvm.cond_br %26, ^bb18, ^bb19
-  ^bb18:  // pred: ^bb17
-    llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%2, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb26
-  ^bb19:  // pred: ^bb17
-    llvm.call @"__predicated_store_!llvm.void_!llvm.ptr<1>_i32_i1_"(%1, %c, %true) : (!llvm.ptr<1>, i32, i1) -> ()
-    llvm.br ^bb26
-  ^bb26:  // 2 preds: ^bb24, ^bb25
-    llvm.br ^bb27
-  ^bb27:  // 2 preds: ^bb13, ^bb26
+    llvm.br ^bb3
+
+  ^bb3:  // 2 preds: ^bb1, ^bb2
     llvm.return
   }
 }