[llvm] [llvm-exegesis] Exclude loads/stores from aliasing instruction set (PR #156300)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-tools-llvm-exegesis

Author: Sjoerd Meijer (sjoerdmeijer)

<details>
<summary>Changes</summary>

In the serial snippet generator and function that computes the aliasing instructions, I don't think we want to include load/store instructions to create a chain as that could make the results more unreliable.

There is a hasMemoryOperands() check, but I think that's an X86 way for checking for loads/stores. For AArch64, we should check mayLoad() and mayStore(), and probably for other architectures too.

---
Full diff: https://github.com/llvm/llvm-project/pull/156300.diff


2 Files Affected:

- (added) llvm/test/tools/llvm-exegesis/AArch64/no-aliasing-ld-str.s (+8) 
- (modified) llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp (+2) 


``````````diff
diff --git a/llvm/test/tools/llvm-exegesis/AArch64/no-aliasing-ld-str.s b/llvm/test/tools/llvm-exegesis/AArch64/no-aliasing-ld-str.s
new file mode 100644
index 0000000000000..65e1203bb275d
--- /dev/null
+++ b/llvm/test/tools/llvm-exegesis/AArch64/no-aliasing-ld-str.s
@@ -0,0 +1,8 @@
+REQUIRES: aarch64-registered-target
+
+RUN: llvm-exegesis -mtriple=aarch64 -mcpu=neoverse-v2 -mode=latency --dump-object-to-disk=%d --opcode-name=FMOVWSr --benchmark-phase=assemble-measured-code 2>&1
+RUN: llvm-objdump -d %d > %t.s
+RUN: FileCheck %s < %t.s
+
+CHECK-NOT: ld{{[1-4]}}
+CHECK-NOT: st{{[1-4]}}
diff --git a/llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp b/llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp
index bdfc93e22273b..551da570685d2 100644
--- a/llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp
+++ b/llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp
@@ -57,6 +57,8 @@ computeAliasingInstructions(const LLVMState &State, const Instruction *Instr,
       continue;
     if (OtherInstr.hasMemoryOperands())
       continue;
+    if (OtherInstr.Description.mayLoad() || OtherInstr.Description.mayStore())
+      continue;
     if (!ET.allowAsBackToBack(OtherInstr))
       continue;
     if (Instr->hasAliasingRegistersThrough(OtherInstr, ForbiddenRegisters))

``````````

</details>


https://github.com/llvm/llvm-project/pull/156300