[PATCH] [SelectionDAG] Fix PR23603.

[Sanjoy Das]

Hi hfinkel, reames,

LLVM's MI level notion of invariant_load is different from LLVM's IR
level notion of invariant_load with respect to dereferenceability.  The
IR notion of invariant_load only guarantees that all *non-faulting*
invariant loads result in the same value.  The MI notion of invariant
load guarantees that the load can be legally moved to any location
within its containing function.  The MI notion of invariant_load is
stronger than the IR notion of invariant_load -- an MI invariant_load is
an IR invariant_load + a guarantee that the location being loaded from
is dereferenceable throughout the function's lifetime.

http://reviews.llvm.org/D10075

Files:
  lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  test/CodeGen/X86/pr23603.ll

Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2848,7 +2848,8 @@
 
   bool isVolatile = I.isVolatile();
   bool isNonTemporal = I.getMetadata(LLVMContext::MD_nontemporal) != nullptr;
-  bool isInvariant = I.getMetadata(LLVMContext::MD_invariant_load) != nullptr;
+  bool isInvariant = I.getMetadata(LLVMContext::MD_invariant_load) != nullptr &&
+    isDereferenceablePointer(SV, *DAG.getTarget().getDataLayout());
   unsigned Alignment = I.getAlignment();
 
   AAMDNodes AAInfo;
Index: test/CodeGen/X86/pr23603.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/pr23603.ll
@@ -0,0 +1,24 @@
+; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck %s
+
+declare void @free_v()
+
+define void @f(i32* %x, i32 %c32, i32* %y) {
+; CHECK-LABEL: f
+ entry:
+  %v = load i32, i32* %x, !invariant.load !0
+; CHECK: movl (%rdi), %ebx
+; CHECK: free_v
+; CHECK-NOT: movl (%rdi), %ebx
+  call void @free_v()
+  %c = icmp ne i32 %c32, 0
+  br i1 %c, label %left, label %merge
+
+ left:
+  store i32 %v, i32* %y
+  br label %merge
+
+ merge:
+  ret void
+}
+
+!0 = !{}

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