[KeyInstr][Clang] For stmt atom #134646
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[KeyInstr][Clang] For stmt atom #134646
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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
This was referenced Apr 7, 2025
This was referenced Apr 7, 2025
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This was referenced Apr 7, 2025
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-clang-codegen Author: Orlando Cazalet-Hyams (OCHyams) ChangesThis patch is part of a stack that teaches Clang to generate Key Instructions The Key Instructions project is introduced, including a "quick summary" section The feature is only functional in LLVM if LLVM is built with CMake flag The Clang-side work is demoed here: Full diff: https://github.com/llvm/llvm-project/pull/134646.diff 2 Files Affected:
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index d9fd406ad64ee..65b71c39d86c4 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -1324,6 +1324,7 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
Continue = getJumpDestInCurrentScope("for.inc");
BreakContinueStack.push_back(BreakContinue(LoopExit, Continue));
+ llvm::BasicBlock *ForBody = nullptr;
if (S.getCond()) {
// If the for statement has a condition scope, emit the local variable
// declaration.
@@ -1348,7 +1349,7 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
ExitBlock = createBasicBlock("for.cond.cleanup");
// As long as the condition is true, iterate the loop.
- llvm::BasicBlock *ForBody = createBasicBlock("for.body");
+ ForBody = createBasicBlock("for.body");
// C99 6.8.5p2/p4: The first substatement is executed if the expression
// compares unequal to 0. The condition must be a scalar type.
@@ -1362,7 +1363,14 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
BoolCondVal = emitCondLikelihoodViaExpectIntrinsic(
BoolCondVal, Stmt::getLikelihood(S.getBody()));
- Builder.CreateCondBr(BoolCondVal, ForBody, ExitBlock, Weights);
+ auto *I = Builder.CreateCondBr(BoolCondVal, ForBody, ExitBlock, Weights);
+ // Key Instructions: Emit the condition and branch as separate atoms to
+ // match existing loop stepping behaviour. 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 *I = dyn_cast<llvm::Instruction>(BoolCondVal))
+ addInstToNewSourceAtom(I, nullptr);
+ addInstToNewSourceAtom(I, nullptr);
if (ExitBlock != LoopExit.getBlock()) {
EmitBlock(ExitBlock);
@@ -1416,6 +1424,12 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
if (CGM.shouldEmitConvergenceTokens())
ConvergenceTokenStack.pop_back();
+
+ if (ForBody) {
+ // Key Instructions: We want the for closing brace to be step-able on to
+ // match existing behaviour.
+ addInstToNewSourceAtom(ForBody->getTerminator(), nullptr);
+ }
}
void
diff --git a/clang/test/KeyInstructions/for.c b/clang/test/KeyInstructions/for.c
new file mode 100644
index 0000000000000..3221ece69a717
--- /dev/null
+++ b/clang/test/KeyInstructions/for.c
@@ -0,0 +1,37 @@
+// RUN: %clang -gkey-instructions -x c++ %s -gmlt -S -emit-llvm -o - \
+// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
+
+// RUN: %clang -gkey-instructions -x c %s -gmlt -S -emit-llvm -o - \
+// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
+
+// Perennial quesiton: should the inc be its own source atom or not
+// (currently it is).
+
+// FIXME: See do.c and while.c regarding cmp and cond br groups.
+
+void a(int A) {
+// CHECK: entry:
+// CHECK: store i32 0, ptr %i{{.*}}, !dbg [[G1R1:!.*]]
+// CHECK: for.cond:
+// CHECK: %cmp = icmp slt i32 %0, %1, !dbg [[G2R1:!.*]]
+// CHECK: br i1 %cmp, label %for.body, label %for.end, !dbg [[G3R1:!.*]]
+
+// FIXME: Added uncond br group here which is useful for O0, which we're
+// no longer targeting. With optimisations loop rotate puts the condition
+// into for.inc and simplifycfg smooshes that and for.body together, so
+// it's not clear whether it adds any value.
+// CHECK: for.body:
+// CHECK: br label %for.inc, !dbg [[G5R1:!.*]]
+
+// CHECK: for.inc:
+// CHECK: %inc = add{{.*}}, !dbg [[G4R2:!.*]]
+// CHECK: store i32 %inc, ptr %i{{.*}}, !dbg [[G4R1:!.*]]
+ for (int i = 0; i < A; ++i) { }
+}
+
+// CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)
+// CHECK: [[G2R1]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 1)
+// CHECK: [[G3R1]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 1)
+// CHECK: [[G5R1]] = !DILocation({{.*}}, atomGroup: 5, atomRank: 1)
+// CHECK: [[G4R2]] = !DILocation({{.*}}, atomGroup: 4, atomRank: 2)
+// CHECK: [[G4R1]] = !DILocation({{.*}}, atomGroup: 4, atomRank: 1)
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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