[llvm] [AArch64] Don't try to sink and(load) (PR #122274)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: David Green (davemgreen)

<details>
<summary>Changes</summary>

If we sink the and in and(load), CGP can hoist is back again to the load, getting into an infinite loop. This prevents sinking the and in this case.

Fixes #<!-- -->122074

---
Full diff: https://github.com/llvm/llvm-project/pull/122274.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp (+4-1) 
- (modified) llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll (+46) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 29ea098386cec1..932a6f9ce23fd2 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -5514,7 +5514,10 @@ bool AArch64TTIImpl::isProfitableToSinkOperands(
         NumZExts++;
       }
 
-      Ops.push_back(&Insert->getOperandUse(1));
+      // And(Load) is excluded to prevent CGP getting stuck in a loop of sinking
+      // the And, just to hoist it again back to the load.
+      if (!match(OperandInstr, m_And(m_Load(m_Value()), m_Value())))
+        Ops.push_back(&Insert->getOperandUse(1));
       Ops.push_back(&Shuffle->getOperandUse(0));
       Ops.push_back(&Op);
     }
diff --git a/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll b/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll
index 95c54cd8b01511..60781466f0eb79 100644
--- a/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll
+++ b/llvm/test/CodeGen/AArch64/aarch64-dup-ext-crash.ll
@@ -40,3 +40,49 @@ vector.body:                                      ; preds = %vector.body, %vecto
   store <2 x i32> %3, ptr %4, align 4
   br label %vector.body
 }
+
+; This test got stuck in a loop hoisting the and to the load, and sinking it back to the mull
+define i32 @dup_and_load(ptr %p, i1 %c) {
+; CHECK-LABEL: dup_and_load:
+; CHECK:       // %bb.0: // %for.body.lr.ph
+; CHECK-NEXT:    mov x8, x0
+; CHECK-NEXT:    ldrb w0, [x0]
+; CHECK-NEXT:    tbz w1, #0, .LBB1_3
+; CHECK-NEXT:  // %bb.1: // %ph
+; CHECK-NEXT:    dup v0.8h, w0
+; CHECK-NEXT:    mov w9, wzr
+; CHECK-NEXT:  .LBB1_2: // %vector.body
+; CHECK-NEXT:    // =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    ldr d1, [x8]
+; CHECK-NEXT:    add w9, w9, #1
+; CHECK-NEXT:    cmp w9, #100
+; CHECK-NEXT:    ushll v1.8h, v1.8b, #0
+; CHECK-NEXT:    umull2 v2.4s, v0.8h, v1.8h
+; CHECK-NEXT:    umull v1.4s, v0.4h, v1.4h
+; CHECK-NEXT:    stp q1, q2, [x8]
+; CHECK-NEXT:    b.lt .LBB1_2
+; CHECK-NEXT:  .LBB1_3: // %end
+; CHECK-NEXT:    ret
+for.body.lr.ph:
+  %l = load i32, ptr %p
+  %conv314 = and i32 %l, 255
+  br i1 %c, label %ph, label %end
+
+ph:
+  %broadcast.splatinsert = insertelement <8 x i32> poison, i32 %conv314, i32 0
+  %broadcast.splat = shufflevector <8 x i32> %broadcast.splatinsert, <8 x i32> poison, <8 x i32> zeroinitializer
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %vector.ph
+  %iv = phi i32 [ 0, %ph ], [ %iv.next, %vector.body ]
+  %wide.load = load <8 x i8>, ptr %p, align 4
+  %0 = zext <8 x i8> %wide.load to <8 x i32>
+  %1 = mul <8 x i32> %broadcast.splat, %0
+  store <8 x i32> %1, ptr %p, align 4
+  %iv.next = add i32 %iv, 1
+  %e = icmp slt i32 %iv.next, 100
+  br i1 %e, label %vector.body, label %end
+
+end:
+  ret i32 %conv314
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/122274