[SelectionDAG] Fix PR23603.

Summary:
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.

Reviewers: hfinkel, reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10075

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238881 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 03a9aa8189afbda9a6dbae4f81147d1686966f2a..9a81ec51ddad4a71ab4a959c24c9fd3e51f9707b 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2848,7 +2848,17 @@ void SelectionDAGBuilder::visitLoad(const LoadInst &I) {
 
   bool isVolatile = I.isVolatile();
   bool isNonTemporal = I.getMetadata(LLVMContext::MD_nontemporal) != nullptr;
-  bool isInvariant = I.getMetadata(LLVMContext::MD_invariant_load) != nullptr;
+
+  // 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
+  // with a guarantee that the location being loaded from is dereferenceable
+  // throughout the function's lifetime.
+
+  bool isInvariant = I.getMetadata(LLVMContext::MD_invariant_load) != nullptr &&
+    isDereferenceablePointer(SV, *DAG.getTarget().getDataLayout());
   unsigned Alignment = I.getAlignment();
 
   AAMDNodes AAInfo;

diff --git a/test/CodeGen/X86/pr23603.ll b/test/CodeGen/X86/pr23603.ll
new file mode 100644 (file)
index 0000000..6f856ae
--- /dev/null
+++ b/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 = !{}