[MachineSink][AArch64] Enable sink-and-fold by default

[momchil-velikov]

Enable the optimisation by default for AArch64 after a compile time regressoin fix in e8209b2

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Momchil Velikov (momchil-velikov)

Changes

Enable the optimisation by default for AArch64 after a compile time regressoin fix in e8209b2

---

Full diff: https://github.com/llvm/llvm-project/pull/72132.diff

1 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64TargetMachine.cpp (+1-1)

diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index 3d818c76bd4b7d7..fcc30a7cfceaf47 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -200,7 +200,7 @@ static cl::opt<bool> EnableGISelLoadStoreOptPostLegal(
 static cl::opt<bool>
     EnableSinkFold("aarch64-enable-sink-fold",
                    cl::desc("Enable sinking and folding of instruction copies"),
-                   cl::init(false), cl::Hidden);
+                   cl::init(true), cl::Hidden);
 
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64Target() {
   // Register the target.

[davemgreen]

With the last debug info being fixed, this still LGTM. Thanks for pushing this through.

(You can probably remove the command line from llvm/test/CodeGen/AArch64/sink-and-fold.ll again).

[antmox]

Hello! It looks like this patch broke lldb-aarch64-ubuntu : https://lab.llvm.org/buildbot/#/builders/96/builds/48609
Could you please look at this ?

[TNorthover]

Another potential problem, I'm afraid. Seen in https://green.lab.llvm.org/green/job/test-suite-verify-machineinstrs-aarch64-O3, but I think this reduced case still shows it:

define i32 @unaspack212(ptr %image, i32 %ep) {
entry:
  %add149 = add i32 %ep, 1
  %idxprom150 = zext i32 %add149 to i64
  %arrayidx151 = getelementptr i8, ptr %image, i64 %idxprom150
  br label %land.lhs.true55

land.lhs.true55:                                  ; preds = %if.then155, %land.lhs.true55, %entry
  %0 = load i8, ptr %arrayidx151, align 1
  %cmp153 = icmp eq i8 %0, 0
  br i1 %cmp153, label %if.then155, label %land.lhs.true55

if.then155:                                       ; preds = %land.lhs.true55
  store i32 0, ptr %image, align 1
  br label %land.lhs.true55
}

compiled with llc -verify-machineinstrs. Basically the sinking leaves a dangling ORRWrs that was part of the zext and marks the register we care about killed.

[momchil-velikov]

Looking at it...

[momchil-velikov]

Addressed in #75072