2 files changed, 36 insertions, 4 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index 13f0cb3900f..0351c33c28e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1684,10 +1684,13 @@ unsigned FastISel::fastEmit_ri_(MVT VT, unsigned Opcode, unsigned Op0,
     MaterialReg = getRegForValue(ConstantInt::get(ITy, Imm));
     if (!MaterialReg)
       return 0;
-    // If this constant was already materialized, then we don't want to kill it.
-    // In this case we will have a use.
-    if (!MRI.use_empty(MaterialReg))
-      IsImmKill = false;
+    // FIXME: If the materialized register here has no uses yet then this
+    // will be the first use and we should be able to mark it as killed.
+    // However, the local value area for materialising constant expressions
+    // grows down, not up, which means that any constant expressions we generate
+    // later which also use 'Imm' could be after this instruction and therefore
+    // after this kill.
+    IsImmKill = false;
   }
   return fastEmit_rr(VT, VT, Opcode, Op0, Op0IsKill, MaterialReg, IsImmKill);
 }
diff --git a/llvm/test/CodeGen/ARM/fast-isel-remat-same-constant.ll b/llvm/test/CodeGen/ARM/fast-isel-remat-same-constant.ll
new file mode 100644
index 00000000000..d64cf8022ed
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/fast-isel-remat-same-constant.ll
@@ -0,0 +1,29 @@
+; RUN: llc %s -o - -fast-isel=true -O0 -verify-machineinstrs | FileCheck %s
+
+target datalayout = "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32"
+target triple = "thumbv7-apple-ios8.0.0"
+
+; This test failed with verify machine instrs due to incorrect kill flags on the add instructions
+; generated by the GEPs.  The first add generated killed the vreg for the #6680 constant which should
+; be correct.  However, the second add is also a constant expression and the local value save area grows
+; down.  This meant the next use of the vreg for #6680 was after the first which had killed it.
+
+; CHECK: #6680
+
+%struct.RD_8x8DATA = type { i32, [16 x [16 x i32]], [16 x [16 x i32]], [16 x [16 x i32]], [3 x [16 x [16 x i32]]], [4 x i16], [4 x i8], [4 x i8], [4 x i8], [16 x [16 x i16]], [16 x [16 x i16]], [16 x [16 x i32]] }
+
+@tr8x8 = external global %struct.RD_8x8DATA, align 4
+@tr4x4 = external global %struct.RD_8x8DATA, align 4
+
+; Function Attrs: noreturn
+declare void @foo(i16*, i16*) #0
+
+; Function Attrs: minsize
+define i32 @test() #1 {
+bb:
+  call void @foo(i16* getelementptr inbounds (%struct.RD_8x8DATA, %struct.RD_8x8DATA* @tr8x8, i32 0, i32 10, i32 0, i32 0), i16* getelementptr inbounds (%struct.RD_8x8DATA, %struct.RD_8x8DATA* @tr4x4, i32 0, i32 10, i32 0, i32 0))
+  unreachable
+}
+
+attributes #0 = { noreturn }
+attributes #1 = { minsize }