[UpdateTestChecks] Don't fail silently when conflicting CHECK lines means no checks are generated for some functions

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/Inputs/conflicting-prefixes.ll

@@ -0,0 +1,16 @@
+; RUN: sed 's/RETVAL/1/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKA %s
+; RUN: sed 's/RETVAL/2/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKA %s
+; RUN: sed 's/RETVAL/3/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKB %s
+; RUN: sed 's/RETVAL/4/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKB %s
+
+define i32 @foo() {
+  ret i32 RETVAL
+}
+
+define i32 @bar() {
+  ret i32 100
+}

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/Inputs/conflicting-prefixes.ll.expected

@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --no-generate-body-for-unused-prefixes
+; RUN: sed 's/RETVAL/1/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKA %s
+; RUN: sed 's/RETVAL/2/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKA %s
+; RUN: sed 's/RETVAL/3/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKB %s
+; RUN: sed 's/RETVAL/4/g' %s | llc -mtriple=riscv32 \
+; RUN:   | FileCheck -check-prefixes=CHECK,CHECKB %s
+
+define i32 @foo() {
+  ret i32 RETVAL
+}
+
+define i32 @bar() {
+; CHECK-LABEL: bar:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    li a0, 100
+; CHECK-NEXT:    ret
+  ret i32 100
+}

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/conflicting-prefixes.test

@@ -0,0 +1,7 @@
+# REQUIRES: riscv-registered-target
+
+# RUN: cp -f %S/Inputs/conflicting-prefixes.ll %t.ll
+# RUN: %update_llc_test_checks --no-generate-body-for-unused-prefixes %t.ll 2>&1 | FileCheck %s
+# RUN: diff -u %S/Inputs/conflicting-prefixes.ll.expected %t.ll
+
+# CHECK: WARNING: For function 'foo', the following RUN lines will not generate checks due to conflicting output

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/prefix-never-matches.test

@@ -4,5 +4,5 @@
 # RUN: %update_llc_test_checks --no-generate-body-for-unused-prefixes %t.ll 2>&1 | FileCheck %s
 # RUN: FileCheck --input-file=%t.ll %s --check-prefix=OUTPUT
 
-# CHECK: WARNING: Prefix A had conflicting output
+# CHECK: WARNING: For function 'fold_v2i64', the following RUN lines will not generate checks due to conflicting output
 # OUTPUT-NOT: A:

llvm/utils/UpdateTestChecks/common.py

@@ -882,6 +882,7 @@ def __str__(self):
 
 class FunctionTestBuilder:
     def __init__(self, run_list, flags, scrubber_args, path, ginfo):
+        self._run_list = run_list
         self._verbose = flags.verbose
         self._record_args = flags.function_signature
         self._check_attributes = flags.check_attributes
@@ -917,15 +918,49 @@ def __init__(self, run_list, flags, scrubber_args, path, ginfo):
                 self._func_order.update({prefix: []})
                 self._global_var_dict.update({prefix: dict()})
 
+    # Return true if there is conflicting output for different runs for the
+    # given prefix and function name.
+    def has_conflicting_output(self, prefix, func):
+        # There was conflicting output if the func_dict is None for this
+        # prefix and function.
+        return self._func_dict[prefix].get(func) is None
+
     def finish_and_get_func_dict(self):
-        for prefix in self.get_failed_prefixes():
-            warn(
-                "Prefix %s had conflicting output from different RUN lines for all functions in test %s"
-                % (
-                    prefix,
-                    self._path,
+        all_funcs = set()
+        for prefix in self._func_dict:
+            all_funcs.update(self._func_dict[prefix].keys())
+
+        warnings_to_print = collections.defaultdict(list)
+        for func in sorted(list(all_funcs)):
+            for i, run_info in enumerate(self._run_list):
+                prefixes = run_info[0]
+                if not prefixes:
+                    continue
+
+                # Check if this RUN line produces this function at all. If
+                # not, we can skip analysing this function for this RUN.
+                run_contains_func = all(func in self._func_dict.get(p, {}) for p in prefixes)
+                if not run_contains_func:
+                    continue
+
+                # Check if this RUN line can print any checks for this
+                # function. It can't if all of its prefixes have conflicting
+                # (None) output.
+                can_print_for_this_run = not all(self.has_conflicting_output(p, func) for p in prefixes)
+                if not can_print_for_this_run:
+                    warnings_to_print[func].append((i, prefixes))
+
+        for func, warning_info in warnings_to_print.items():
+            conflict_strs = []
+            for run_index, prefixes in warning_info:
+                conflict_strs.append(
+                     f"RUN #{run_index + 1} (prefixes: {', '.join(prefixes)})"
                 )
+            warn(
+                f"For function '{func}', the following RUN lines will not generate checks due to conflicting output: {', '.join(conflict_strs)}",
+                test_file=self._path,
             )
+
         return self._func_dict
 
     def func_order(self):
@@ -1078,20 +1113,6 @@ def processed_prefixes(self, prefixes):
         """
         self._processed_prefixes.update(prefixes)
 
-    def get_failed_prefixes(self):
-        # This returns the list of those prefixes that failed to match any function,
-        # because there were conflicting bodies produced by different RUN lines, in
-        # all instances of the prefix.
-        for prefix in self._func_dict:
-            if self._func_dict[prefix] and (
-                not [
-                    fct
-                    for fct in self._func_dict[prefix]
-                    if self._func_dict[prefix][fct] is not None
-                ]
-            ):
-                yield prefix
-
 
 ##### Generator of LLVM IR CHECK lines