[GCRelocate] Add a peephole to canonicalize base pointer relocation

If we generate the gc.relocate, and then later prove two arguments to the statepoint are equivalent, we should canonicalize the gc.relocate to the form we would have produced if this had been known before rewriting.

llvm-svn: 372771

2 files changed, 23 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 0b4e9e9af3c..5c0e648f490 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3951,10 +3951,21 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     break;
   }
   case Intrinsic::experimental_gc_relocate: {
+    auto &GCR = *cast<GCRelocateInst>(II);
+
+    // If we have two copies of the same pointer in the statepoint argument
+    // list, canonicalize to one.  This may let us common gc.relocates.
+    if (GCR.getBasePtr() == GCR.getDerivedPtr() &&
+        GCR.getBasePtrIndex() != GCR.getDerivedPtrIndex()) {
+      auto *OpIntTy = GCR.getOperand(2)->getType();
+      II->setOperand(2, ConstantInt::get(OpIntTy, GCR.getBasePtrIndex()));
+      return II;
+    }
+    
     // Translate facts known about a pointer before relocating into
     // facts about the relocate value, while being careful to
     // preserve relocation semantics.
-    Value *DerivedPtr = cast<GCRelocateInst>(II)->getDerivedPtr();
+    Value *DerivedPtr = GCR.getDerivedPtr();
 
     // Remove the relocation if unused, note that this check is required
     // to prevent the cases below from looping forever.
diff --git a/llvm/test/Transforms/InstCombine/gc.relocate.ll b/llvm/test/Transforms/InstCombine/gc.relocate.ll
index 78b3b5f42f9..f8eade6f11f 100644
--- a/llvm/test/Transforms/InstCombine/gc.relocate.ll
+++ b/llvm/test/Transforms/InstCombine/gc.relocate.ll
@@ -52,6 +52,17 @@ entry:
   ret <2 x i8 addrspace(1)*> %obj.relocated
 }
 
+define i32 addrspace(1)* @canonical_base(i32 addrspace(1)* %dparam) gc "statepoint-example" {
+; Checks that a nonnull pointer
+; CHECK-LABEL: @canonical_base
+; CHECK: (token %tok, i32 7, i32 7) ; (%dparam, %dparam)
+entry:
+  %tok = tail call token (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 0, i32 addrspace(1)* %dparam, i32 addrspace(1)* %dparam)
+  %relocate = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token %tok,  i32 7, i32 8)
+  ret i32 addrspace(1)* %relocate
+}
+
+
 declare void @do_safepoint()
 
 declare token @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32, void ()*, i32, i32, ...)