54d544b831
This patch is part of a stack that teaches Clang to generate Key Instructions metadata for C and C++. When returning a value, stores to the `retval` allocas and branches to `return` block are put in the same atom group. They are both rank 1, which could in theory introduce an extra step in some optimized code. This low risk currently feels an acceptable for keeping the code a bit simpler (as opposed to adding scaffolding to make the store rank 2). In the case of a single return (no control flow) the return instruction inherits the atom group of the branch to the return block when the blocks get folded togather. 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.
37 lines
1.7 KiB
C
37 lines
1.7 KiB
C
// RUN: %clang_cc1 -triple x86_64-linux-gnu -gkey-instructions -x c++ -std=c++17 %s -debug-info-kind=line-tables-only -emit-llvm -o - \
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// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
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// RUN: %clang_cc1 -triple x86_64-linux-gnu -gkey-instructions -x c %s -debug-info-kind=line-tables-only -emit-llvm -o - \
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// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
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// Perennial question: should the `dec` be in its own source atom or not
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// (currently it is).
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// Another question - we've made the cmp and br separate source atoms for
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// now, to match existing behaviour in this case:
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// 1. do {
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// 2. something();
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// 3. }
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// 4. while (--A);
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// Non key instruction behaviour is: 2, 4[, 3, 2, 4]+
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// The cond br is associated with the brace on line 3 and the cmp is line 4;
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// if they were in the same atom group we'd step just: 2, 3[, 2, 3]+
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// FIXME: We could arguably improve the behaviour by making them the same
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// group but having the cmp higher precedence, resulting in: 2, 4[, 2, 4]+.
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void a(int A) {
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// CHECK: %dec = add nsw i32 %0, -1, !dbg [[G1R2:!.*]]
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// CHECK: store i32 %dec, ptr %A.addr{{.*}}, !dbg [[G1R1:!.*]]
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// CHECK: %tobool = icmp ne i32 %dec, 0, !dbg [[G2R1:!.*]]
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// CHECK: br i1 %tobool, label %do.body, label %do.end, !dbg [[G3R1:!.*]], !llvm.loop
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do { } while (--A);
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// CHECK: ret{{.*}}, !dbg [[RET:!.*]]
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}
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// CHECK: [[G1R2]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 2)
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// CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)
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// CHECK: [[G2R1]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 1)
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// CHECK: [[G3R1]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 1)
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// CHECK: [[RET]] = !DILocation({{.*}}, atomGroup: 4, atomRank: 1)
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