[KeyInstr][Clang] Catch variable init atom

[OCHyams]

This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.

The Key Instructions project is introduced, including a "quick summary" section
at the top which adds context for this PR, here:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668

The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.

The Clang-side work is demoed here:
#130943

[OCHyams]

• [NFC][KeyInstr][Clang] Add some additional tests #134654
• [KeyInstr][Clang] Coerced store atoms #134653
• [KeyInstr][Clang] Ret atom #134652
• [KeyIntsr][Clang] Builtins alloca auto-init atom #134651
• [KeyInstr][Clang] Assign matrix element atom #134650
• [KeyInstr][Clang] Assign vector element atom #134649
• [KeyInstr][Clang] Bitfield atom #134648
• [KeyInstr][Clang] For range stmt atoms #134647
• [KeyInstr][Clang] For stmt atom #134646
• [KeyInstr][Clang] While stmt atom #134645
• [KeyInstr][Clang] Do stmt atom #134644
• [KeyInstr][Clang] Switch stmt atom #134643
• [KeyInstr][Clang] If stmt atom #134642
• [KeyInstr][Clang] Catch variable init atom #134641 👈 (View in Graphite)
• [KeyInstr][Clang] Member initalization atom #134640
• [KeyInstr][Clang] Aggregate init + copy #134639
• [KeyInstr] Complex assignment atoms #134638
• [KeyInstr][Clang] Assignment atom group #134637
• [KeyInstr][Clang] Static variable init atom #134636
• [KeyInstr][Clang] Agg init atom #134635
• [Clang][NFC] Move some static functions into CodeGenFunction #134634
• [KeyInstr][Clang] Scalar init atom #134633
• [KeyInstr][Clang] Add ApplyAtomGroup #134632
• [KeyInstr][Clang] Add Clang option -g[no-]key-instructions #134627
• [KeyInstr][DwarfDebug] Add is_stmt emission support #133495
• [KeyInstr] Add MIR parser support #133494
• [KeyInstr] Remap cloned PHIs in BreakCriticalEdges #133493
• Propagate DebugLocs on phis in BreakCriticalEdges #133492
• [KeyInstr][LoopUnswitch] Remap cloned instructions' atoms #133491
• [KeyInstr][LoopRotate] Remap atoms of duplicated instructions #133490
• [KeyInstr][LoopUnroll] Remap atoms while unrolling #133489
• [KeyInstr][JumpThreading] Remap atoms duping bb with cond br on phi into pred #133488
• [KeyInstr][JumpThreading] Remap atoms after threading #133487
• [KeyInstr][JumpThreading] Remap atoms in blocks duplicated for threading #133486
• [KeyInstr][Inline] Don't propagate atoms to inlined nodebug instructions #133485
• [KeyInstr][SimplifyCFG] Remap atoms after duplication for threading #133484
• [KeyInstr][debugify] Add --debugify-atoms to add key instructions metadata #133483
• [KeyInstr][SimplifyCFG] Remap atoms when folding br to common succ into pred #133482
• [KeyInstr] Inline atom info #133481
• [KeyInstr] Merge atoms in DILocation::getMergedLocation #133480
• [NFC][KeyInstr] Add Atom Group (re)mapping #133479
• [KeyInstr] Add Atom Group waterline to LLVMContext #133478
• [KeyInstr] Add fields to DILocation behind compile time flag #133477
• main

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[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Orlando Cazalet-Hyams (OCHyams)

Changes

This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.

The Key Instructions project is introduced, including a "quick summary" section
at the top which adds context for this PR, here:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668

The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.

The Clang-side work is demoed here:
#130943

---

Full diff: https://github.com/llvm/llvm-project/pull/134641.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/ItaniumCXXABI.cpp (+1)
• (added) clang/test/KeyInstructions/try-catch.cpp (+20)

diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 77e995b4c933a..b3f1e208fa318 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -5051,6 +5051,7 @@ void ItaniumCXXABI::emitBeginCatch(CodeGenFunction &CGF,
 
   // Emit the local.
   CodeGenFunction::AutoVarEmission var = CGF.EmitAutoVarAlloca(*CatchParam);
+  ApplyAtomGroup Grp(CGF.getDebugInfo());
   InitCatchParam(CGF, *CatchParam, var.getObjectAddress(CGF), S->getBeginLoc());
   CGF.EmitAutoVarCleanups(var);
 }
diff --git a/clang/test/KeyInstructions/try-catch.cpp b/clang/test/KeyInstructions/try-catch.cpp
new file mode 100644
index 0000000000000..3d1080aca2f07
--- /dev/null
+++ b/clang/test/KeyInstructions/try-catch.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang -gkey-instructions %s -gmlt -S -emit-llvm -o - -fexceptions \
+// RUN: | FileCheck %s
+
+void except() {
+  // FIXME(OCH): Should `store i32 32, ptr %exception` be key?
+  throw 32;
+}
+
+void attempt() {
+  try { except(); }
+// CHECK: catch:
+// CHECK: %4 = call ptr @__cxa_begin_catch(ptr %exn)
+// CHECK: %5 = load i32{{.*}}, !dbg [[G1R2:!.*]]
+// CHECK: store i32 %5, ptr %e{{.*}}, !dbg [[G1R1:!.*]]
+// CHECK: call void @__cxa_end_catch()
+  catch (int e) { }
+}
+
+// CHECK: [[G1R2]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 2)
+// CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)

[jmorse]

Looking good, with a question inline.

[jmorse]

Risk that a destructor for the catch-parameter could be given this instruction group?

[OCHyams]

Yes if a few things were different and wrong. 1. Calls aren't annotated. 2. If they were, it would be a bug if whatever call handling code didn't have its own ApplyAtomGroup for the dtor.

I could add a scope around ApplyAtomGroup and InitCatchParam, and/or add more tests, if you think it would be useful?

[jmorse]

Hmmm -- yes please for the braces, no worries about the tests. This is just about reducing the amount of potentially-unexpected behaviour

[jmorse]

(LGTM with the braces)