[PATCH] D31954: [InstCombine] Retain TBAA when narrowing loads

[Keno Fischer via Phabricator via llvm-commits]

loladiro created this revision.

As discussed on the mailing list it is legal to propagate TBAA to loads from
smaller regions of a larger load tagged with TBAA. Do so for
(load->extractvalue)=>(gep->load) folding.


https://reviews.llvm.org/D31954

Files:
  lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  lib/Transforms/InstCombine/InstructionCombining.cpp
  test/Transforms/InstCombine/extractval-tbaa.ll


Index: test/Transforms/InstCombine/extractval-tbaa.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/extractval-tbaa.ll
@@ -0,0 +1,16 @@
+; RUN: opt -S -instcombine %s -o - | FileCheck %s
+
+%Complex = type { double, double }
+
+; Check that instcombine preserves TBAA when narrowing loads
+define double @test(%Complex *%val) {
+; CHECK: load double, {{.*}}, !tbaa
+; CHECK-NOT: load %Complex
+    %loaded = load %Complex, %Complex *%val, !tbaa !1
+    %real = extractvalue %Complex %loaded, 0
+    ret double %real
+}
+
+!0 = !{!"tbaa_root"}
+!1 = !{!2, !2, i64 0}
+!2 = !{!"Complex", !0, i64 0}
Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2430,9 +2430,15 @@
       Builder->SetInsertPoint(L);
       Value *GEP = Builder->CreateInBoundsGEP(L->getType(),
                                               L->getPointerOperand(), Indices);
+      Instruction *Load = Builder->CreateLoad(GEP);
+      // Whatever aliasing information we had for the orignal load must also
+      // hold for the smaller load, so propagate the annotations.
+      AAMDNodes Nodes;
+      L->getAAMetadata(Nodes);
+      Load->setAAMetadata(Nodes);
       // Returning the load directly will cause the main loop to insert it in
       // the wrong spot, so use replaceInstUsesWith().
-      return replaceInstUsesWith(EV, Builder->CreateLoad(GEP));
+      return replaceInstUsesWith(EV, Load);
     }
   // We could simplify extracts from other values. Note that nested extracts may
   // already be simplified implicitly by the above: extract (extract (insert) )
Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -701,6 +701,10 @@
                                                 Name + ".elt");
       auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
       auto *L = IC.Builder->CreateAlignedLoad(Ptr, EltAlign, Name + ".unpack");
+      // Propagate AA metadata. It'll still be valid on the narrowed load.
+      AAMDNodes AAMD;
+      LI.getAAMetadata(AAMD);
+      L->setAAMetadata(AAMD);
       V = IC.Builder->CreateInsertValue(V, L, i);
     }
 


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