[profcheck] Add unknown branch weights for inlined strcmp/strncmp

[jinhuang1102]

The strcmp/strncmp inliner creates new conditional branches but was failing to add profile metadata. This caused the ProfileVerifierPass to fail when profcheck is enabled.

This patch fixes the issue by explicitly adding unknown branch weights to these branches.

Issue #147390

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Jin Huang (jinhuang1102)

Changes

The strcmp/strncmp inliner creates new conditional branches but was failing to add profile metadata. This caused the ProfileVerifierPass to fail when profcheck is enabled.

This patch fixes the issue by explicitly adding unknown branch weights to these branches.

---

Full diff: https://github.com/llvm/llvm-project/pull/160455.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp (+8-4)

diff --git a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
index 40de36d81ddd2..d00a3bc86d6b8 100644
--- a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
+++ b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
@@ -29,6 +29,7 @@
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/ProfDataUtils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/BuildLibCalls.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -1283,11 +1284,14 @@ void StrNCmpInliner::inlineCompare(Value *LHS, StringRef RHS, uint64_t N,
     Value *VR =
         ConstantInt::get(CI->getType(), static_cast<unsigned char>(RHS[i]));
     Value *Sub = Swapped ? B.CreateSub(VR, VL) : B.CreateSub(VL, VR);
-    if (i < N - 1)
-      B.CreateCondBr(B.CreateICmpNE(Sub, ConstantInt::get(CI->getType(), 0)),
-                     BBNE, BBSubs[i + 1]);
-    else
+    if (i < N - 1) {
+      BranchInst *CondBrInst = B.CreateCondBr(
+          B.CreateICmpNE(Sub, ConstantInt::get(CI->getType(), 0)), BBNE,
+          BBSubs[i + 1]);
+      setExplicitlyUnknownBranchWeights(*CondBrInst, DEBUG_TYPE);
+    } else {
       B.CreateBr(BBNE);
+    }
 
     Phi->addIncoming(Sub, BBSubs[i]);
   }

[mtrofin]

Set this only if the function entry count is non-zero. See this discussion: #158743 (comment)

[mtrofin]

you also need a unittest. You could modify or clone the one that failed originally, to also have a function entry count and then you can check the unknown insertion.

[tmsri]

This looks good with a unit test and the entry count change.

[jinhuang1102]

Added the entry_count checking and modified the IR test case for !prof check.

[mtrofin]

(took the liberty and added the reference to the tracking issue)

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[jinhuang1102]

@mtrofin Add function entry count and check for unknown insert here.

[mtrofin]

I think you need to give main here its function_entry_count !prof explicitly, otherwise this only passes in the build with profcheck enabled.

otherwise lgtm

[mtrofin]

nit: place a space after !8

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-aarch64-quick running on linaro-clang-aarch64-quick while building llvm at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/23166

Here is the relevant piece of the build log for the reference

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests/44/332' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-3983049-44-332.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=332 GTEST_SHARD_INDEX=44 /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests
--

Script:
--
/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests --gtest_filter=ClangdServerTest.Reparse
--
ASTWorker building file /clangd-test/foo.cpp version null with command 
[/clangd-test]
clang -ffreestanding /clangd-test/foo.cpp
Driver produced command: cc1 -cc1 -triple aarch64-unknown-linux-gnu -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name foo.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -ffreestanding -enable-tlsdesc -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir lib/clang/22 -internal-isystem lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /clangd-test/foo.cpp
Building first preamble for /clangd-test/foo.cpp version null
../llvm/clang-tools-extra/clangd/unittests/ClangdTests.cpp:241: Failure
Value of: Server.blockUntilIdleForTest()
  Actual: false
Expected: true
Waiting for diagnostics

Built preamble of size 740008 for file /clangd-test/foo.cpp version null in 17.16 seconds

../llvm/clang-tools-extra/clangd/unittests/ClangdTests.cpp:241
Value of: Server.blockUntilIdleForTest()
  Actual: false
Expected: true
Waiting for diagnostics



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