update_test_checks: keep meta variables stable by default

Resubmitting this after previous revert with the following changes:

- Split table into table_rhs_idx and table_candidate_idx so that
  bisect.bisect_left can be used without the `key` argument, which
  was introduced in Python 3.10
- Remove a re.Pattern type annotation

Original commit message:

Prior to this change, running UTC on larger tests, especially tests
with unnamed IR values, often resulted in a spuriously large diff
because e.g. TMPnn variables in the CHECK lines were renumbered. This
change attempts to reduce the diff by keeping those variable names the
same.

There are cases in which this "drift" of variable names can end up being
more confusing. The old behavior can be re-enabled with the
--reset-variable-names command line argument.

The improvement may not be immediately apparent in the diff of this change.
The point is that the diff of stable_ir_values.ll against
stable_ir_values.ll.expected after this change is smaller.

Ideally, we'd also keep meta variables for "global" objects stable, e.g.
for attributes (#nn) and metadata (!nn). However, that would require a
much more substantial refactoring of how we generate check lines, so I
left it for future work.

Author: nhaehnle

llvm/test/tools/UpdateTestChecks/update_test_checks/Inputs/stable_ir_values.ll.expected

@@ -9,11 +9,11 @@
 define i32 @func({i32, i32} %x, i32 %y) {
 ; CHECK-LABEL: define i32 @func(
 ; CHECK-SAME: { i32, i32 } [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[X_I34:%.*]] = extractvalue { i32, i32 } [[X]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[Y]], 1
-; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[X_I34]], [[TMP1]]
-; CHECK-NEXT:    [[TMP3:%.*]] = mul i32 [[TMP2]], 3
-; CHECK-NEXT:    ret i32 [[TMP3]]
+; CHECK-NEXT:    [[X_I33:%.*]] = extractvalue { i32, i32 } [[X]], 0
+; CHECK-NEXT:    [[TMP3:%.*]] = add i32 [[Y]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[X_I33]], [[TMP3]]
+; CHECK-NEXT:    [[TMP2:%.*]] = mul i32 [[TMP1]], 3
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %x.i34 = extractvalue {i32, i32} %x, 0
   %1 = add i32 %y, 1

llvm/test/tools/UpdateTestChecks/update_test_checks/Inputs/stable_ir_values.ll.expected.reset

@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt < %s -S | FileCheck %s
+
+; The assumption underlying this test is that there are pre-existing check lines
+; but something has changed, and we would like to avoid needless changes of
+; meta variable names so that diffs end up being easier to read, e.g. avoid
+; changing X_I33 into X_I34 or renumbering the various TMP variables.
+
+define i32 @func({i32, i32} %x, i32 %y) {
+; CHECK-LABEL: define i32 @func(
+; CHECK-SAME: { i32, i32 } [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[X_I34:%.*]] = extractvalue { i32, i32 } [[X]], 0
+; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[Y]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[X_I34]], [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = mul i32 [[TMP2]], 3
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;
+  %x.i34 = extractvalue {i32, i32} %x, 0
+  %1 = add i32 %y, 1
+  %2 = add i32 %x.i34, %1
+  %3 = mul i32 %2, 3
+  ret i32 %3
+}

llvm/test/tools/UpdateTestChecks/update_test_checks/Inputs/stable_ir_values2.ll.expected

@@ -5,12 +5,12 @@ define i32 @func(i32 %x) {
 ; CHECK-LABEL: define i32 @func(
 ; CHECK-SAME: i32 [[X:%.*]]) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[X]], 0
-; CHECK-NEXT:    [[TMP2:%.*]] = call i32 @foo(i1 [[TMP1]])
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[X]], 2
-; CHECK-NEXT:    [[TMP4:%.*]] = call i32 @foo(i1 [[TMP3]])
-; CHECK-NEXT:    [[TMP5:%.*]] = icmp ne i32 [[TMP4]], 0
-; CHECK-NEXT:    [[TMP6:%.*]] = select i1 [[TMP5]], i32 [[TMP4]], i32 [[TMP2]]
-; CHECK-NEXT:    ret i32 [[TMP6]]
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @foo(i1 [[TMP1]])
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i32 [[X]], 2
+; CHECK-NEXT:    [[TMP8:%.*]] = call i32 @foo(i1 [[TMP7]])
+; CHECK-NEXT:    [[TMP9:%.*]] = icmp ne i32 [[TMP8]], 0
+; CHECK-NEXT:    [[TMP10:%.*]] = select i1 [[TMP9]], i32 [[TMP8]], i32 [[TMP6]]
+; CHECK-NEXT:    ret i32 [[TMP10]]
 ;
   %1 = icmp eq i32 %x, 0
   %2 = call i32 @foo(i1 %1)

llvm/test/tools/UpdateTestChecks/update_test_checks/Inputs/stable_ir_values3.ll

@@ -1,9 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
 ; RUN: opt < %s -S | FileCheck %s
 
-; Test that we don't regress diff quality by trying to keep variable names
-; stable (and messing up the matching).
-
 define i32 @func(i32 %x) {
 ; CHECK-LABEL: define i32 @func(
 ; CHECK-SAME: i32 [[X:%.*]]) {

llvm/test/tools/UpdateTestChecks/update_test_checks/Inputs/stable_ir_values3.ll.expected

@@ -1,9 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
 ; RUN: opt < %s -S | FileCheck %s
 
-; Test that we don't regress diff quality by trying to keep variable names
-; stable (and messing up the matching).
-
 define i32 @func(i32 %x) {
 ; CHECK-LABEL: define i32 @func(
 ; CHECK-SAME: i32 [[X:%.*]]) {

llvm/test/tools/UpdateTestChecks/update_test_checks/Inputs/stable_ir_values4.ll.expected

@@ -15,12 +15,12 @@ define i32 @func(i32 %x) {
 ; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @foo(i32 [[TMP5]])
 ; CHECK-NEXT:    [[TMP7:%.*]] = call i32 @foo(i32 [[TMP6]])
 ; CHECK-NEXT:    [[TMP8:%.*]] = xor i32 [[TMP7]], 1
-; CHECK-NEXT:    [[TMP9:%.*]] = call i32 @foo(i32 [[TMP8]])
-; CHECK-NEXT:    [[TMP10:%.*]] = add i32 [[TMP9]], 1
+; CHECK-NEXT:    [[TMP13:%.*]] = call i32 @foo(i32 [[TMP8]])
+; CHECK-NEXT:    [[TMP9:%.*]] = add i32 [[TMP13]], 1
+; CHECK-NEXT:    [[TMP10:%.*]] = call i32 @foo(i32 [[TMP9]])
 ; CHECK-NEXT:    [[TMP11:%.*]] = call i32 @foo(i32 [[TMP10]])
 ; CHECK-NEXT:    [[TMP12:%.*]] = call i32 @foo(i32 [[TMP11]])
-; CHECK-NEXT:    [[TMP13:%.*]] = call i32 @foo(i32 [[TMP12]])
-; CHECK-NEXT:    ret i32 [[TMP13]]
+; CHECK-NEXT:    ret i32 [[TMP12]]
 ;
   %1 = mul i32 %x, 3
   %2 = call i32 @foo(i32 %1)

llvm/test/tools/UpdateTestChecks/update_test_checks/stable_ir_values.test

@@ -1,2 +1,5 @@
 # RUN: cp -f %S/Inputs/stable_ir_values.ll %t.ll && %update_test_checks %t.ll
 # RUN: diff -u %t.ll %S/Inputs/stable_ir_values.ll.expected
+# Now test that we can reset all the names
+# RUN: %update_test_checks %t.ll --reset-variable-names
+# RUN: diff -u %t.ll %S/Inputs/stable_ir_values.ll.expected.reset