[PATCH] D138283: [SVE] Enhanced loop access analysis

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A loop contains only the constant initial value array, and no memory dependency check is required.


https://reviews.llvm.org/D138283

Files:
  llvm/lib/Analysis/LoopAccessAnalysis.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/const-value-initialize-small-loop.ll


Index: llvm/test/Transforms/LoopVectorize/AArch64/const-value-initialize-small-loop.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopVectorize/AArch64/const-value-initialize-small-loop.ll
@@ -0,0 +1,50 @@
+; RUN: opt < %s -loop-vectorize -mtriple=aarch64--linux-gnu -mattr=+sve -disable-output -debug-only=loop-accesses 2>&1 | FileCheck %s
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+;
+; CHECK-LABEL:  test
+; CHECK:        LAA: There are only constant initial values in a loop, ignore memory dependency checks.
+;
+
+define void @test(i8* %excl_flags_buff.1.us, i32* %0, i32* %full_excl.049.us, i64 %indvars.iv, i32* %arrayidx9.us, i8* %excl_flags_buff.050.us) {
+for.body.us.preheader:
+  br label %for.body.us
+
+for.body.us:                                      ; preds = %if.end.us, %for.body.us.preheader
+  %excl_flags_buff.050.us1 = phi i8* [ %excl_flags_buff.1.us, %if.end.us ], [ null, %for.body.us.preheader ]
+  %full_excl.049.us2 = phi i32* [ %0, %if.end.us ], [ null, %for.body.us.preheader ]
+  br i1 false, label %if.else.us, label %if.then.us
+
+if.then.us:                                       ; preds = %for.body.us
+  br i1 false, label %if.end.us, label %for.body7.us.preheader
+
+for.body7.us.preheader:                           ; preds = %if.then.us
+  br label %for.body7.us
+
+for.body7.us:                                     ; preds = %for.body7.us, %for.body7.us.preheader
+  %indvars.iv3 = phi i64 [ 0, %for.body7.us.preheader ], [ %indvars.iv.next, %for.body7.us ]
+  %arrayidx9.us4 = getelementptr inbounds i32, i32* %full_excl.049.us, i64 %indvars.iv
+  %1 = load i32, i32* %0, align 4
+  %idxprom10.us = sext i32 %1 to i64
+  %arrayidx11.us = getelementptr inbounds i8, i8* %excl_flags_buff.050.us, i64 %idxprom10.us
+  store i8 0, i8* %arrayidx11.us, align 1
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv3, 1
+  br i1 true, label %if.end.us.loopexit, label %for.body7.us
+
+if.else.us:                                       ; preds = %for.body.us
+  br label %if.end.us
+
+if.end.us.loopexit:                               ; preds = %for.body7.us
+  br label %if.end.us
+
+if.end.us:                                        ; preds = %if.end.us.loopexit, %if.else.us, %if.then.us
+  %excl_flags_buff.1.us5 = phi i8* [ null, %if.else.us ], [ %excl_flags_buff.1.us, %if.then.us ], [ null, %if.end.us.loopexit ]
+  %2 = load i32*, i32** null, align 8
+  br label %for.body.us
+}
+
+; Function Attrs: argmemonly nofree nounwind willreturn writeonly
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg) #0
+
+attributes #0 = { argmemonly nofree nounwind willreturn writeonly }
+
Index: llvm/lib/Analysis/LoopAccessAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -2169,6 +2169,8 @@
 
   bool HasComplexMemInst = false;
 
+  bool IsConstantVal = true;
+
   // A runtime check is only legal to insert if there are no convergent calls.
   HasConvergentOp = false;
 
@@ -2301,6 +2303,10 @@
 
   for (StoreInst *ST : Stores) {
     Value *Ptr = ST->getPointerOperand();
+    Value *Val = ST->getValueOperand();
+
+    if (!isa<ConstantData>(Val))
+      IsConstantVal = false;
 
     if (isUniform(Ptr)) {
       // Record store instructions to loop invariant addresses
@@ -2338,6 +2344,14 @@
     return;
   }
 
+  if (IsConstantVal) {
+    LLVM_DEBUG(
+        dbgs() << "LAA: There are only constant initial values in a loop, ignore memory dependency "
+               << "checks.\n");
+    CanVecMem = true;
+    return;
+  }
+
   for (LoadInst *LD : Loads) {
     Value *Ptr = LD->getPointerOperand();
     // If we did *not* see this pointer before, insert it to the


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