[PATCH] D75704: [RS4GC] Handle uses of extractelement for conversion from vector to scalar base

[Anna Thomas via Phabricator via llvm-commits]

anna created this revision.
anna added reviewers: reames, skatkov, dantrushin.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

As mentioned in the comments, extractelement is special
since we actually want a scalar base for that element we extracted from
the vector (i.e. not a vector base).
This same logic should apply to uses of the extractelement such as phis
and selects which have the same BDV as the extractelement.

Added testcase showcases the problem where the BDV identification chokes
on the incorrect cast from vector to scalar for the phi use of
extractelement.

Tests-Run: make check


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75704

Files:
  llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
  llvm/test/Transforms/RewriteStatepointsForGC/scalar-base-vector.ll


Index: llvm/test/Transforms/RewriteStatepointsForGC/scalar-base-vector.ll
===================================================================
--- llvm/test/Transforms/RewriteStatepointsForGC/scalar-base-vector.ll
+++ llvm/test/Transforms/RewriteStatepointsForGC/scalar-base-vector.ll
@@ -141,3 +141,55 @@
   %ptr = extractelement <2 x i32 addrspace(1)*> %vec, i32 0
   ret i32 addrspace(1)* %ptr
 }
+
+define void @test6() gc "statepoint-example" {
+; CHECK-LABEL: @test6(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label [[HEADER:%.*]]
+; CHECK:       header:
+; CHECK-NEXT:    [[TMP_BASE:%.*]] = phi i8 addrspace(1)* [ [[BASE_EE:%.*]], [[LATCH:%.*]] ], [ null, [[BB:%.*]] ], !is_base_value !0
+; CHECK-NEXT:    [[TMP:%.*]] = phi i8 addrspace(1)* [ [[TMP6:%.*]], [[LATCH]] ], [ undef, [[BB]] ]
+; CHECK-NEXT:    br label [[BB10:%.*]]
+; CHECK:       bb10:
+; CHECK-NEXT:    [[STATEPOINT_TOKEN:%.*]] = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000, i32 0, void ()* @spam, i32 0, i32 0, i32 0, i32 1, i8 addrspace(1)* [[TMP]], i8 addrspace(1)* [[TMP]], i8 addrspace(1)* [[TMP_BASE]])
+; CHECK-NEXT:    [[TMP_RELOCATED:%.*]] = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token [[STATEPOINT_TOKEN]], i32 9, i32 8)
+; CHECK-NEXT:    [[TMP_BASE_RELOCATED:%.*]] = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token [[STATEPOINT_TOKEN]], i32 9, i32 9)
+; CHECK-NEXT:    br label [[BB25:%.*]]
+; CHECK:       bb25:
+; CHECK-NEXT:    [[STATEPOINT_TOKEN1:%.*]] = call token (i64, i32, <2 x i8 addrspace(1)*> ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_v2p1i8f(i64 2882400000, i32 0, <2 x i8 addrspace(1)*> ()* @baz, i32 0, i32 0, i32 0, i32 0)
+; CHECK-NEXT:    [[TMP262:%.*]] = call <2 x i8 addrspace(1)*> @llvm.experimental.gc.result.v2p1i8(token [[STATEPOINT_TOKEN1]])
+; CHECK-NEXT:    [[BASE_EE]] = extractelement <2 x i8 addrspace(1)*> [[TMP262]], i32 0, !is_base_value !0
+; CHECK-NEXT:    [[TMP27:%.*]] = extractelement <2 x i8 addrspace(1)*> [[TMP262]], i32 0
+; CHECK-NEXT:    br i1 undef, label [[BB7:%.*]], label [[LATCH]]
+; CHECK:       bb7:
+; CHECK-NEXT:    br label [[LATCH]]
+; CHECK:       latch:
+; CHECK-NEXT:    [[TMP6]] = phi i8 addrspace(1)* [ [[TMP27]], [[BB25]] ], [ [[TMP27]], [[BB7]] ]
+; CHECK-NEXT:    br label [[HEADER]]
+;
+bb:
+  br label %header
+
+header:                                              ; preds = %latch, %bb
+  %tmp = phi i8 addrspace(1)* [ %tmp6, %latch ], [ undef, %bb ]
+  br label %bb10
+
+bb10:                                             ; preds = %bb2
+  call void @spam() [ "deopt"(i8 addrspace(1)* %tmp) ]
+  br label %bb25
+
+bb25:                                             ; preds = %bb24
+  %tmp26 = call <2 x i8 addrspace(1)*> @baz()
+  %tmp27 = extractelement <2 x i8 addrspace(1)*> %tmp26, i32 0
+  br i1 undef, label %bb7, label %latch
+
+bb7:                                              ; preds = %bb25
+  br label %latch
+
+latch:                                              ; preds = %bb25, %bb7
+  %tmp6 = phi i8 addrspace(1)* [ %tmp27, %bb25 ], [ %tmp27, %bb7 ]
+  br label %header
+}
+
+declare void @spam()
+declare <2 x i8 addrspace(1)*> @baz()
Index: llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -948,6 +948,16 @@
           State.getBaseValue(), EE->getIndexOperand(), "base_ee", EE);
       BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
       States[I] = BDVState(BDVState::Base, BaseInst);
+      // Uses of the above EE instruction which have a scalar base and the same
+      // state as the EE instruction's (i.e. vector base) should also be updated
+      // to have this new base.
+      for (User *U : I->users()) {
+        auto *UseI = dyn_cast<Instruction>(U);
+        if (!UseI || !States.count(UseI))
+          continue;
+        if (!isa<VectorType>(UseI->getType()) && States[UseI] == State)
+          States[UseI] = BDVState(BDVState::Base, BaseInst);
+      }
     }
 
     // Since we're joining a vector and scalar base, they can never be the
@@ -1008,7 +1018,11 @@
   auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) {
     Value *BDV = findBaseOrBDV(Input, Cache);
     Value *Base = nullptr;
-    if (isKnownBaseResult(BDV)) {
+    // Avoid the optimization of choosing a KnownBase BDV when the BDV is a
+    // vector type, while the input is scalar.
+    const bool VectorTypeBDV =
+        isa<VectorType>(BDV->getType()) && !isa<VectorType>(Input->getType());
+    if (isKnownBaseResult(BDV) && !VectorTypeBDV) {
       Base = BDV;
     } else {
       // Either conflict or base.


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