[CodeGen][test] Use -fno-discard-value-names for better test support

[rupprecht]

Summary

Depending on how clang is built, it may discard the IR names and use names like %2 instead of %result.ptr, causing tests that rely on the IR name to fail. Using fno-discard-value-names ensures the actual name is present regardless of the build mode.

[akhuang]

Looks good, alternatively I think we can just change %result.ptr into a variable match?

[lebedev.ri]

In D63625#1552756, @akhuang wrote:

Looks good, alternatively I think we can just change %result.ptr into a variable match?

Why isn't this using FileCheck variable matching in the first place? That's the least fragile solution.

[akhuang]

Why isn't this using FileCheck variable matching in the first place? That's the least fragile solution.

No reason, just something I overlooked when I wrote it-

[rupprecht]

• Use filecheck variable matching instead of an explicit -fno-discard-value-names option

[rupprecht]

Sounds good, changed to use variable matching instead. This passes w/ either -fno-discard-value-names or -fdiscard-value-names used.

[akhuang]

lgtm

[rnk]

Thanks. This is surprisingly the first time I've heard of fdiscard-value-names. Seems useful, since now you can test your IR both ways without having to completely recompile clang.

clang/test/CodeGenCXX/debug-info-nrvo.cpp

-// RUN: %clangxx -target x86_64-unknown-unknown -g %s -emit-llvm -S -o - | FileCheck %s
-// RUN: %clangxx -target x86_64-unknown-unknown -g -fno-elide-constructors %s -emit-llvm -S -o - | FileCheck %s -check-prefix=NOELIDE
+// RUN: %clangxx -target x86_64-unknown-unknown -g \
+// RUN:   %s -emit-llvm -S -o - | FileCheck %s
+
+// RUN: %clangxx -target x86_64-unknown-unknown -g \
+// RUN:   -fno-elide-constructors %s -emit-llvm -S -o - | \
+// RUN:   FileCheck %s -check-prefix=NOELIDE
+
 struct Foo {
   Foo() = default;
   Foo(Foo &&other) { x = other.x; }
   int x;
 };
 void some_function(int);
 Foo getFoo() {
   Foo foo;
   foo.x = 41;
   some_function(foo.x);
   return foo;
 }
 
 int main() {
   Foo bar = getFoo();
   return bar.x;
 }
 
 // Check that NRVO variables are stored as a pointer with deref if they are
 // stored in the return register.
 
-// CHECK: %result.ptr = alloca i8*, align 8
-// CHECK: call void @llvm.dbg.declare(metadata i8** %result.ptr,
+// CHECK: %[[RESULT:.*]] = alloca i8*, align 8
+// CHECK: call void @llvm.dbg.declare(metadata i8** %[[RESULT]],
 // CHECK-SAME: metadata !DIExpression(DW_OP_deref)
-// NOELIDE: call void @llvm.dbg.declare(metadata %struct.Foo* %foo,
+
+// NOELIDE: %[[FOO:.*]] = alloca %struct.Foo, align 4
+// NOELIDE: call void @llvm.dbg.declare(metadata %struct.Foo* %[[FOO]],
 // NOELIDE-SAME:                        metadata !DIExpression()