[llvm] [AArch64] Verify ldp/stp alignment stricter (PR #84124)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Yuta Mukai (ytmukai)

<details>
<summary>Changes</summary>

When ldp-aligned-only/stp-aligned-only is specified, modified to cancel ldp/stp transformation if MachineMemOperand is not present or the access size is unknown.
In the previous implementation, the test passed when there was no MachineMemOperand. Also, if the size was unknown, an incorrect value was used or an assertion failed. (But actually, if there is no MachineMemOperand, it will be excluded from the target by isCandidateToMergeOrPair() before reaching the part.)

A statistic NumFailedAlignmentCheck is added. NumPairCreated is modified so that it only counts if it is not canceled.

---
Full diff: https://github.com/llvm/llvm-project/pull/84124.diff


1 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp (+25-19) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
index 926a89466255ca..0ab2c401b1749d 100644
--- a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
@@ -62,6 +62,8 @@ STATISTIC(NumUnscaledPairCreated,
           "Number of load/store from unscaled generated");
 STATISTIC(NumZeroStoresPromoted, "Number of narrow zero stores promoted");
 STATISTIC(NumLoadsFromStoresPromoted, "Number of loads from stores promoted");
+STATISTIC(NumFailedAlignmentCheck, "Number of load/store pair transformation "
+                                   "not passed the alignment check");
 
 DEBUG_COUNTER(RegRenamingCounter, DEBUG_TYPE "-reg-renaming",
               "Controls which pairs are considered for renaming");
@@ -2337,9 +2339,6 @@ bool AArch64LoadStoreOpt::tryToPairLdStInst(MachineBasicBlock::iterator &MBBI) {
   MachineBasicBlock::iterator Paired =
       findMatchingInsn(MBBI, Flags, LdStLimit, /* FindNarrowMerge = */ false);
   if (Paired != E) {
-    ++NumPairCreated;
-    if (TII->hasUnscaledLdStOffset(MI))
-      ++NumUnscaledPairCreated;
     // Keeping the iterator straight is a pain, so we let the merge routine tell
     // us what the next instruction is after it's done mucking about.
     auto Prev = std::prev(MBBI);
@@ -2349,24 +2348,31 @@ bool AArch64LoadStoreOpt::tryToPairLdStInst(MachineBasicBlock::iterator &MBBI) {
     MachineMemOperand *MemOp =
         MI.memoperands_empty() ? nullptr : MI.memoperands().front();
 
-    // Get the needed alignments to check them if
-    // ldp-aligned-only/stp-aligned-only features are opted.
-    uint64_t MemAlignment = MemOp ? MemOp->getAlign().value() : -1;
-    uint64_t TypeAlignment = MemOp ? Align(MemOp->getSize()).value() : -1;
+    // If a load/store arrives and ldp/stp-aligned-only feature is opted, check
+    // that the alignment of the source pointer is at least double the alignment
+    // of the type.
+    if ((MI.mayLoad() && Subtarget->hasLdpAlignedOnly()) ||
+        (MI.mayStore() && Subtarget->hasStpAlignedOnly())) {
+      // If there is no size/align information, cancel the transformation.
+      if (!MemOp || !MemOp->getMemoryType().isValid()) {
+        NumFailedAlignmentCheck++;
+        return false;
+      }
 
-    // If a load arrives and ldp-aligned-only feature is opted, check that the
-    // alignment of the source pointer is at least double the alignment of the
-    // type.
-    if (MI.mayLoad() && Subtarget->hasLdpAlignedOnly() && MemOp &&
-        MemAlignment < 2 * TypeAlignment)
-      return false;
+      // Get the needed alignments to check them if
+      // ldp-aligned-only/stp-aligned-only features are opted.
+      uint64_t MemAlignment = MemOp->getAlign().value();
+      uint64_t TypeAlignment = Align(MemOp->getSize()).value();
 
-    // If a store arrives and stp-aligned-only feature is opted, check that the
-    // alignment of the source pointer is at least double the alignment of the
-    // type.
-    if (MI.mayStore() && Subtarget->hasStpAlignedOnly() && MemOp &&
-        MemAlignment < 2 * TypeAlignment)
-      return false;
+      if (MemAlignment < 2 * TypeAlignment) {
+        NumFailedAlignmentCheck++;
+        return false;
+      }
+    }
+
+    ++NumPairCreated;
+    if (TII->hasUnscaledLdStOffset(MI))
+      ++NumUnscaledPairCreated;
 
     MBBI = mergePairedInsns(MBBI, Paired, Flags);
     // Collect liveness info for instructions between Prev and the new position

``````````

</details>


https://github.com/llvm/llvm-project/pull/84124