[InstCombine] Use more inline elements in a SmallVector

[kazutakahirata]

The 4 inline elements only cover 58% of cases encountered here during
the compilation of X86ISelLowering.cpp.ll, a .ll version of
X86ISelLowering.cpp.

The 8 inline elements cover 96% and save 0.27% of heap allocations.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Kazu Hirata (kazutakahirata)

Changes

The 4 inline elements only cover 58% of cases encountered here during
the compilation of X86ISelLowering.cpp.ll, a .ll version of
X86ISelLowering.cpp.

The 8 inline elements cover 96% and save 0.27% of heap allocations.

---

Full diff: https://github.com/llvm/llvm-project/pull/100942.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+1-1)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index f6c4b6e180937..e61480d7542d7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1500,7 +1500,7 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   // Don't try to simplify calls without uses. It will not do anything useful,
   // but will result in the following folds being skipped.
   if (!CI.use_empty()) {
-    SmallVector<Value *, 4> Args;
+    SmallVector<Value *, 8> Args;
     Args.reserve(CI.arg_size());
     for (Value *Op : CI.args())
       Args.push_back(Op);

[nikic]

LGTM

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-armv8-quick running on linaro-clang-armv8-quick while building llvm at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/2038

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

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'ClangPseudo :: lex.c' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 11: clang-pseudo -source /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang-tools-extra/pseudo/test/lex.c -print-source | /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang-tools-extra/pseudo/test/lex.c -check-prefix=SOURCE --strict-whitespace
+ clang-pseudo -source /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang-tools-extra/pseudo/test/lex.c -print-source
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang-tools-extra/pseudo/test/lex.c -check-prefix=SOURCE --strict-whitespace
clang-pseudo: ../llvm/clang-tools-extra/pseudo/lib/cxx/CXX.cpp:437: auto clang::pseudo::cxx::getLanguage()::(anonymous class)::operator()() const: Assertion `Diags.empty()' failed.
#0 0x00c391d0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang-pseudo+0x5e1d0)
#1 0x00c36f38 llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang-pseudo+0x5bf38)
#2 0x00c39c3c SignalHandler(int) Signals.cpp:0:0
#3 0xf755e530 __default_sa_restorer /build/glibc-tftl1u/glibc-2.31/signal/../sysdeps/unix/sysv/linux/arm/sigrestorer.S:67:0
#4 0xf754e7e6 /build/glibc-tftl1u/glibc-2.31/csu/../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:47:0
#5 0xf755d7fe raise /build/glibc-tftl1u/glibc-2.31/signal/../sysdeps/unix/sysv/linux/raise.c:28:1
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang-tools-extra/pseudo/test/lex.c -check-prefix=SOURCE --strict-whitespace

--

********************

[topperc]

Can this be rewritten as

SmallVector<Value *, 8> Args(CI.arg_begin(), CI.arg_end());

[kazutakahirata]

Yes, thank you for bringing this up. It can actually be even shorter:

SmallVector<Value *, 8> Args(CI.args());

I'll post a follow-up PR.