[llvm] [AArch64] Fix v4i8 loads in strict-align mode. (PR #95828)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Eli Friedman (efriedma-quic)

<details>
<summary>Changes</summary>

Fixes #<!-- -->95811

---
Full diff: https://github.com/llvm/llvm-project/pull/95828.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64ISelLowering.cpp (+4) 
- (modified) llvm/test/CodeGen/AArch64/aarch64-load-ext.ll (+47) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 360a841bdade4..78fcc0bbad7ca 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -6406,6 +6406,10 @@ SDValue AArch64TargetLowering::LowerLOAD(SDValue Op,
   if (LoadNode->getMemoryVT() != MVT::v4i8)
     return SDValue();
 
+  // Avoid generating unaligned loads.
+  if (Subtarget->requiresStrictAlign() && LoadNode->getAlign() < Align(4))
+    return SDValue();
+
   unsigned ExtType;
   if (LoadNode->getExtensionType() == ISD::SEXTLOAD)
     ExtType = ISD::SIGN_EXTEND;
diff --git a/llvm/test/CodeGen/AArch64/aarch64-load-ext.ll b/llvm/test/CodeGen/AArch64/aarch64-load-ext.ll
index 945a73b05f1ba..317feb5ad9ad0 100644
--- a/llvm/test/CodeGen/AArch64/aarch64-load-ext.ll
+++ b/llvm/test/CodeGen/AArch64/aarch64-load-ext.ll
@@ -450,3 +450,50 @@ define <4 x i8> @bitcast(i32 %0) {
   %2 = bitcast i32 %0 to <4 x i8>
   ret <4 x i8> %2
 }
+
+define <4 x i8> @strict_align_aligned(ptr %v4i8_ptr) "target-features"="+strict-align" {
+; CHECK-LE-LABEL: strict_align_aligned:
+; CHECK-LE:       // %bb.0:
+; CHECK-LE-NEXT:    ldr s0, [x0]
+; CHECK-LE-NEXT:    ushll v0.8h, v0.8b, #0
+; CHECK-LE-NEXT:    // kill: def $d0 killed $d0 killed $q0
+; CHECK-LE-NEXT:    ret
+;
+; CHECK-BE-LABEL: strict_align_aligned:
+; CHECK-BE:       // %bb.0:
+; CHECK-BE-NEXT:    ldr s0, [x0]
+; CHECK-BE-NEXT:    rev32 v0.8b, v0.8b
+; CHECK-BE-NEXT:    ushll v0.8h, v0.8b, #0
+; CHECK-BE-NEXT:    rev64 v0.4h, v0.4h
+; CHECK-BE-NEXT:    ret
+  %v4i8 = load <4 x i8>, ptr %v4i8_ptr, align 4
+  ret <4 x i8> %v4i8
+}
+
+define <4 x i8> @strict_align_unaligned(ptr %v4i8_ptr) "target-features"="+strict-align" {
+; CHECK-LE-LABEL: strict_align_unaligned:
+; CHECK-LE:       // %bb.0:
+; CHECK-LE-NEXT:    ld1 { v0.b }[0], [x0]
+; CHECK-LE-NEXT:    add x8, x0, #1
+; CHECK-LE-NEXT:    ld1 { v0.b }[2], [x8]
+; CHECK-LE-NEXT:    add x8, x0, #2
+; CHECK-LE-NEXT:    ld1 { v0.b }[4], [x8]
+; CHECK-LE-NEXT:    add x8, x0, #3
+; CHECK-LE-NEXT:    ld1 { v0.b }[6], [x8]
+; CHECK-LE-NEXT:    // kill: def $d0 killed $d0 killed $q0
+; CHECK-LE-NEXT:    ret
+;
+; CHECK-BE-LABEL: strict_align_unaligned:
+; CHECK-BE:       // %bb.0:
+; CHECK-BE-NEXT:    ld1 { v0.b }[0], [x0]
+; CHECK-BE-NEXT:    add x8, x0, #1
+; CHECK-BE-NEXT:    ld1 { v0.b }[2], [x8]
+; CHECK-BE-NEXT:    add x8, x0, #2
+; CHECK-BE-NEXT:    ld1 { v0.b }[4], [x8]
+; CHECK-BE-NEXT:    add x8, x0, #3
+; CHECK-BE-NEXT:    ld1 { v0.b }[6], [x8]
+; CHECK-BE-NEXT:    rev64 v0.4h, v0.4h
+; CHECK-BE-NEXT:    ret
+  %v4i8 = load <4 x i8>, ptr %v4i8_ptr, align 1
+  ret <4 x i8> %v4i8
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/95828