[PATCH 08/27] [noalias] EarlyCSE: learn about noalias intrinsics

[jeroen.dobbelaere]

Summary

This is part of the series started by D68484.

Note: this is a stable point and tests should run fine with the patches applied up to this point.
Note: D68494 has been incorporated.

[lebedev.ri]

Looks ok.

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

939

"EarlyCSE skipping noalias intrinsic: " ?

[jeroen.dobbelaere]

Adapt to changed rebase in D68494

[jeroen.dobbelaere]

Rebased

[jeroen.dobbelaere]

Rebased to c06b7e2ab5167ad031745a706204abed1aefd823 (July 14, 2020)

[jeroen.dobbelaere]

Rebased to 9fb46a452d4e5666828c95610ceac8dcd9e4ce16 (September 7, 2020)

[jeroen.dobbelaere]

Rebased to f8dbd61074176bae92ec360a093ac7bc498c9321.

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

private:
   }
 
   void removeMSSA(Instruction &Inst) {
     if (!MSSA)
       return;
     if (VerifyMemorySSA)
       MSSA->verifyMemorySSA();
     // Removing a store here can leave MemorySSA in an unoptimized state by
     // creating MemoryPhis that have identical arguments and by creating
     // MemoryUses whose defining access is not an actual clobber. The phi case
     // is handled by MemorySSA when passing OptimizePhis = true to
     // removeMemoryAccess.  The non-optimized MemoryUse case is lazily updated
     // by MemorySSA's getClobberingMemoryAccess.
     MSSAUpdater->removeMemoryAccess(&Inst, true);
   }
 };
 
for (Instruction &Inst : make_early_inc_range(BB->getInstList())) {
     // its condition as true for all dominated blocks.
     if (auto *Assume = dyn_cast<AssumeInst>(&Inst)) {
       auto *CondI = dyn_cast<Instruction>(Assume->getArgOperand(0));
       if (CondI && SimpleValue::canHandle(CondI)) {
         LLVM_DEBUG(dbgs() << "EarlyCSE considering assumption: " << Inst
                           << '\n');
         AvailableValues.insert(CondI, ConstantInt::getTrue(BB->getContext()));
       } else
-        LLVM_DEBUG(dbgs() << "EarlyCSE skipping assumption: " << Inst << '\n');
+        LLVM_DEBUG(dbgs() << "EarlyCSE skipping intrinsic: " << Inst << '\n');
+      continue;
+    }
+
+    // Likewise, noalias intrinsics don't actually write.
+    if (match(&Inst, m_Intrinsic<Intrinsic::noalias>()) ||
+        match(&Inst, m_Intrinsic<Intrinsic::noalias_decl>()) ||
+        match(&Inst, m_Intrinsic<Intrinsic::provenance_noalias>()) ||
+        match(&Inst, m_Intrinsic<Intrinsic::noalias_arg_guard>())) {
+      LLVM_DEBUG(dbgs() << "EarlyCSE skipping noalias intrinsic: " << Inst
+                        << '\n');
       continue;
     }
 
     // Likewise, noalias intrinsics don't actually write.
     if (match(&Inst,
               m_Intrinsic<Intrinsic::experimental_noalias_scope_decl>())) {
       LLVM_DEBUG(dbgs() << "EarlyCSE skipping noalias intrinsic: " << Inst
                         << '\n');

llvm/test/Transforms/EarlyCSE/basic.ll

define i32 @test2a(i32 *%P, i1 %b) {
   %V1 = load i32, i32* %P
   tail call void @llvm.assume(i1 %b)
   %V2 = load i32, i32* %P
   %Diff = sub i32 %V1, %V2
   ret i32 %Diff
   ; CHECK: ret i32 0
 }
 
+; CHECK-LABEL: @test2b(
+define i32 @test2b(i32 *%P, i1 %b) {
+  %V1 = load i32, i32* %P
+  call i8* @llvm.noalias.p0i8.p0i8.p0p0i8.i32(i8* undef, i8* null, i8** null, i32 0, metadata !1)
+  %V2 = load i32, i32* %P
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK: ret i32 0
+}
+
+; CHECK-LABEL: @test2c(
+define i32 @test2c(i32 *%P, i1 %b) {
+  %V1 = load i32, i32* %P
+  call i8* @llvm.provenance.noalias.p0i8.p0i8.p0p0i8.p0p0i8.i32(i8* undef, i8* null, i8** null, i8** null, i32 0, metadata !1)
+  %V2 = load i32, i32* %P
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK: ret i32 0
+}
+
 ;; Cross block load value numbering.
 ; CHECK-LABEL: @test3(
 define i32 @test3(i32 *%P, i1 %Cond) {
   %V1 = load i32, i32* %P
   br i1 %Cond, label %T, label %F
 T:
   store i32 4, i32* %P
   ret i32 42

 define i32 @test6a(i32 *%P, i1 %b) {
   store i32 42, i32* %P
   tail call void @llvm.assume(i1 %b)
   %V1 = load i32, i32* %P
   ret i32 %V1
   ; CHECK: ret i32 42
 }
 
+; CHECK-LABEL: @test6b(
+define i32 @test6b(i32 *%P, i1 %b) {
+  store i32 42, i32* %P
+  call i8* @llvm.noalias.p0i8.p0i8.p0p0i8.i32(i8* undef, i8* null, i8** null, i32 0, metadata !1)
+  %V1 = load i32, i32* %P
+  ret i32 %V1
+  ; CHECK: ret i32 42
+}
+
+; CHECK-LABEL: @test6c(
+define i32 @test6c(i32 *%P, i1 %b) {
+  store i32 42, i32* %P
+  call i8* @llvm.provenance.noalias.p0i8.p0i8.p0p0i8.p0p0i8.i32(i8* undef, i8* null, i8** null, i8** null, i32 0, metadata !1)
+  %V1 = load i32, i32* %P
+  ret i32 %V1
+  ; CHECK: ret i32 42
+}
+
 ;; Trivial dead store elimination.
 ; CHECK-LABEL: @test7(
 define void @test7(i32 *%P) {
   store i32 42, i32* %P
   store i32 45, i32* %P
   ret void
   ; CHECK-NEXT: store i32 45
   ; CHECK-NEXT: ret void

 ; CHECK-LABEL: @cse_freeze(
 ; CHECK: %b = freeze i1 %a
 ; CHECK: ret i1 %b
   %b = freeze i1 %a
   %c = freeze i1 %a
   %and = and i1 %b, %c
   ret i1 %and
 }
+
+declare i8*  @llvm.noalias.p0i8.p0i8.p0p0i8.i32(i8*, i8*, i8**, i32, metadata ) nounwind
+declare i8*  @llvm.provenance.noalias.p0i8.p0i8.p0p0i8.p0p0i8.i32(i8*, i8*, i8**, i8**, i32, metadata ) nounwind
+
+!0 = !{!0, !"some domain"}
+!1 = !{!1, !0, !"some scope"}