[clang] 189d5da - [KeyInstr][Clang] Do stmt atom (#134644)
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Fri May 23 06:31:21 PDT 2025
Author: Orlando Cazalet-Hyams
Date: 2025-05-23T14:31:18+01:00
New Revision: 189d5dad364a402c79901cea2c9cdac03b7c5560
URL: https://github.com/llvm/llvm-project/commit/189d5dad364a402c79901cea2c9cdac03b7c5560
DIFF: https://github.com/llvm/llvm-project/commit/189d5dad364a402c79901cea2c9cdac03b7c5560.diff
LOG: [KeyInstr][Clang] Do stmt atom (#134644)
See test comment for possible future improvement.
This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.
RFC:
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.
Added:
clang/test/DebugInfo/KeyInstructions/do.c
Modified:
clang/lib/CodeGen/CGStmt.cpp
Removed:
################################################################################
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index 3562b4ea22a24..ca1e6522ad564 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -1242,9 +1242,18 @@ void CodeGenFunction::EmitDoStmt(const DoStmt &S,
// As long as the condition is true, iterate the loop.
if (EmitBoolCondBranch) {
uint64_t BackedgeCount = getProfileCount(S.getBody()) - ParentCount;
- Builder.CreateCondBr(
+ auto *I = Builder.CreateCondBr(
BoolCondVal, LoopBody, LoopExit.getBlock(),
createProfileWeightsForLoop(S.getCond(), BackedgeCount));
+
+ // Key Instructions: Emit the condition and branch as separate source
+ // location atoms otherwise we may omit a step onto the loop condition in
+ // favour of the closing brace.
+ // FIXME: We could have the branch as the backup location for the condition,
+ // which would probably be a better experience (no jumping to the brace).
+ if (auto *CondI = dyn_cast<llvm::Instruction>(BoolCondVal))
+ addInstToNewSourceAtom(CondI, nullptr);
+ addInstToNewSourceAtom(I, nullptr);
}
LoopStack.pop();
diff --git a/clang/test/DebugInfo/KeyInstructions/do.c b/clang/test/DebugInfo/KeyInstructions/do.c
new file mode 100644
index 0000000000000..f3b2bb465cae8
--- /dev/null
+++ b/clang/test/DebugInfo/KeyInstructions/do.c
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -gkey-instructions -x c++ -std=c++17 %s -debug-info-kind=line-tables-only -emit-llvm -o - \
+// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
+
+// RUN: %clang_cc1 -gkey-instructions -x c %s -debug-info-kind=line-tables-only -emit-llvm -o - \
+// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
+
+// Perennial question: should the `dec` be in its own source atom or not
+// (currently it is).
+
+// Another question - we've made the cmp and br separate source atoms for
+// now, to match existing behaviour in this case:
+// 1. do {
+// 2. something();
+// 3. }
+// 4. while (--A);
+// Non key instruction behaviour is: 2, 4[, 3, 2, 4]+
+// The cond br is associated with the brace on line 3 and the cmp is line 4;
+// if they were in the same atom group we'd step just: 2, 3[, 2, 3]+
+// FIXME: We could arguably improve the behaviour by making them the same
+// group but having the cmp higher precedence, resulting in: 2, 4[, 2, 4]+.
+
+void a(int A) {
+// CHECK: %dec = add nsw i32 %0, -1, !dbg [[G1R2:!.*]]
+// CHECK: store i32 %dec, ptr %A.addr{{.*}}, !dbg [[G1R1:!.*]]
+// CHECK: %tobool = icmp ne i32 %dec, 0, !dbg [[G2R1:!.*]]
+// CHECK: br i1 %tobool, label %do.body, label %do.end, !dbg [[G3R1:!.*]], !llvm.loop
+ do { } while (--A);
+}
+
+// CHECK: [[G1R2]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 2)
+// CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)
+// CHECK: [[G2R1]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 1)
+// CHECK: [[G3R1]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 1)
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