[PATCH] D98147: [SCEV] Improve modelling for pointer constants

[Michael Kruse via Phabricator via llvm-commits]

Meinersbur added a comment.

This is my draft suggestion for changes required in Polly for this change. The main problem is that `isZero()` does not recognize a SCEVUnknown-wrapped ConstantNullExpr.

  diff --git a/polly/lib/Analysis/ScopBuilder.cpp b/polly/lib/Analysis/ScopBuilder.cpp
  index 4def17102925..d7cafb18e633 100644
  --- a/polly/lib/Analysis/ScopBuilder.cpp
  +++ b/polly/lib/Analysis/ScopBuilder.cpp
  @@ -1760,6 +1760,10 @@ bool ScopBuilder::buildAccessMemIntrinsic(MemAccInst Inst, ScopStmt *Stmt) {
     //       as we know it would be undefined to execute this instruction anyway.
     if (DestAccFunc->isZero())
       return true;
  +  if (auto *X = dyn_cast<SCEVUnknown>(DestAccFunc)) {
  +    if (isa<ConstantPointerNull>(X->getValue()))
  +      return true;
  +  }
  
     auto *DestPtrSCEV = dyn_cast<SCEVUnknown>(SE.getPointerBase(DestAccFunc));
     assert(DestPtrSCEV);
  @@ -1836,6 +1840,10 @@ bool ScopBuilder::buildAccessCallInst(MemAccInst Inst, ScopStmt *Stmt) {
         auto *ArgSCEV = SE.getSCEVAtScope(Arg, L);
         if (ArgSCEV->isZero())
           continue;
  +      if (auto *X = dyn_cast<SCEVUnknown>(ArgSCEV)) {
  +        if (isa<ConstantPointerNull>(X->getValue()))
  +          return true;
  +      }
  
         auto *ArgBasePtr = cast<SCEVUnknown>(SE.getPointerBase(ArgSCEV));
         addArrayAccess(Stmt, Inst, AccType, ArgBasePtr->getValue(),
   PWACtx SCEVAffinator::complexityBailout() {
  diff --git a/polly/lib/Support/SCEVValidator.cpp b/polly/lib/Support/SCEVValidator.cpp
  index 94b55167a9b4..0e0ec7358571 100644
  --- a/polly/lib/Support/SCEVValidator.cpp
  +++ b/polly/lib/Support/SCEVValidator.cpp
  @@ -461,6 +461,11 @@ public:
         }
       }
  
  +    if (Expr->getType()->isPointerTy()) {
  +      if (isa<ConstantPointerNull>(V))
  +        return ValidatorResult(SCEVType::INT); // "int"
  +    }
  +
       return ValidatorResult(SCEVType::PARAM, Expr);
     }
   };
  diff --git a/polly/test/Isl/CodeGen/partial_write_impossible_restriction.ll b/polly/test/Isl/CodeGen/partial_write_impossible_restriction.ll
  index e4c2ce20b82b..3b17518a3ef4 100644
  --- a/polly/test/Isl/CodeGen/partial_write_impossible_restriction.ll
  +++ b/polly/test/Isl/CodeGen/partial_write_impossible_restriction.ll
  @@ -7,7 +7,7 @@
   ;
   target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
  
  -define void @partial_write_impossible_restriction() {
  +define void @partial_write_impossible_restriction(i32* %.pn) {
   entry:
     br i1 undef, label %invoke.cont258, label %cond.true.i.i.i.i1007
  
  @@ -15,7 +15,6 @@ cond.true.i.i.i.i1007:
     br label %invoke.cont258
  
   invoke.cont258:
  -  %.pn = phi i32* [ null, %cond.true.i.i.i.i1007 ], [ null, %entry ]
     br label %invoke.cont274
  
   invoke.cont274:                                   ; preds = %invoke.cont258
  @@ -49,11 +48,11 @@ if.then.i.i1141.loopexit:                         ; preds = %cond.end
  
  
   ; CHECK-LABEL: polly.stmt.cond.false:
  -; CHECK:         %polly.access..pn2 = getelementptr i32, i32* %.pn, i64 %polly.indvar
  -; CHECK:         store i32 %cond.in.sroa.speculate.load.cond.false_p_scalar_, i32* %polly.access..pn2, align 4, !alias.scope !0, !noalias !2
  +; CHECK:         %polly.access..pn{{[0-9]*}} = getelementptr i32, i32* %.pn, i64 %polly.indvar
  +; CHECK:         store i32 %cond.in.sroa.speculate.load.cond.false_p_scalar_, i32* %polly.access..pn{{[0-9]*}}, align 4, !alias.scope !0, !noalias !2
   ; CHECK:         br label %polly.merge
  
  -; CHECK-LABEL: polly.stmt.cond.false11:
  -; CHECK:         %polly.access..pn14 = getelementptr i32, i32* %.pn, i64 0
  -; CHECK:         store i32 %cond.in.sroa.speculate.load.cond.false_p_scalar_13, i32* %polly.access..pn14, align 4, !alias.scope !0, !noalias !2
  -; CHECK:         br label %polly.stmt.cond.end15
  +; CHECK-LABEL: polly.stmt.cond.false{{[0-9]*}}:
  +; CHECK:         %polly.access..pn{{[0-9]*}} = getelementptr i32, i32* %.pn, i64 0
  +; CHECK:         store i32 %cond.in.sroa.speculate.load.cond.false_p_scalar_{{[0-9]*}}, i32* %polly.access..pn{{[0-9]*}}, align 4, !alias.scope !0, !noalias !2
  +; CHECK:         br label %polly.stmt.cond.end{{[0-9]*}}
  diff --git a/polly/test/Isl/CodeGen/scev_looking_through_bitcasts.ll b/polly/test/Isl/CodeGen/scev_looking_through_bitcasts.ll
  index 1012e23cd3a2..ea7a9b7976dc 100644
  --- a/polly/test/Isl/CodeGen/scev_looking_through_bitcasts.ll
  +++ b/polly/test/Isl/CodeGen/scev_looking_through_bitcasts.ll
  @@ -31,7 +31,8 @@ bitmap_element_allocate.exit:
   }
  
  
  -; CHECK:       polly.stmt.cond.end73.i:
  -; CHECK-NEXT:   %0 = bitcast %structty** %b.s2a to i8**
  -; CHECK-NEXT:   store i8* undef, i8** %0
  +; CHECK:      polly.stmt.cond.end73.i:
  +; CHECK-NEXT:   %scevgep = getelementptr i8, i8* null, i64 %a
  +; CHECK-NEXT:   %scevgep1 = bitcast i8* %scevgep to %structty*
  +; CHECK-NEXT:   store %structty* %scevgep1, %structty** %b.s2a, align 8
   ; CHECK-NEXT:   br label %polly.exiting


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D98147/new/

https://reviews.llvm.org/D98147