[X86] combineTruncate - drop load alignment after (trunc (srl (load p), amt)) -> (load p + amt/8) fold

[RKSimon]

The pointer adjustment no longer guarantees any alignment

Missed in #165266 and only noticed in some follow up work

[llvmbot]

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Changes

The pointer adjustment no longer guarantees any alignment

Missed in #165266 and only noticed in some follow up work

---

Full diff: https://github.com/llvm/llvm-project/pull/165436.diff

1 Files Affected:

• (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+2-1)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index b86020aa512ea..5785440a20e43 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -54679,7 +54679,8 @@ static SDValue combineTruncate(SDNode *N, SelectionDAG &DAG,
         SDValue NewPtr = DAG.getMemBasePlusOffset(
             Ld->getBasePtr(), PtrByteOfs, DL, SDNodeFlags::NoUnsignedWrap);
         SDValue NewLoad =
-            DAG.getLoad(VT, DL, Ld->getChain(), NewPtr, Ld->getMemOperand());
+            DAG.getLoad(VT, DL, Ld->getChain(), NewPtr, Ld->getPointerInfo(),
+                        Align(), Ld->getMemOperand()->getFlags());
         DAG.ReplaceAllUsesOfValueWith(Src.getOperand(0).getValue(1),
                                       NewLoad.getValue(1));
         return NewLoad;

[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/24637

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/93/335' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-3526613-93-335.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=335 GTEST_SHARD_INDEX=93 /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=TUSchedulerTests.PublishWithStalePreamble
--
ASTWorker building file /clangd-test/foo.cpp version 1 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 1
../llvm/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp:1263: Failure
Failed
Timed out waiting for diags

../llvm/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp:1296: Failure
Value of: BlockForDiags(PI)
Expected: has a first field that is equal to "1", and has a second field that is equal to "1"
  Actual: ("invalid", "version"), whose first field does not match

Built preamble of size 737140 for file /clangd-test/foo.cpp version 1 in 22.06 seconds

../llvm/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp:1263
Failed
Timed out waiting for diags

../llvm/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp:1296
Value of: BlockForDiags(PI)
Expected: has a first field that is equal to "1", and has a second field that is equal to "1"
  Actual: ("invalid", "version"), whose first field does not match



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