Avoid rematerializing a redef immediately after the old def.
PR14098 contains an example where we would rematerialize a MOV8ri
immediately after the original instruction:
%vreg7:sub_8bit<def> = MOV8ri 9; GR32_ABCD:%vreg7
%vreg22:sub_8bit<def> = MOV8ri 9; GR32_ABCD:%vreg7
Besides being pointless, it is also wrong since the original instruction
only redefines part of the register, and the value read by the new
instruction is wrong.
The problem was the LiveRangeEdit::allUsesAvailableAt() didn't
special-case OrigIdx == UseIdx and found the wrong SSA value.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166068 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveRangeEdit.cpp b/lib/CodeGen/LiveRangeEdit.cpp
index 0dfb084..f8fbc7dd 100644
--- a/lib/CodeGen/LiveRangeEdit.cpp
+++ b/lib/CodeGen/LiveRangeEdit.cpp
@@ -96,6 +96,13 @@
const VNInfo *OVNI = li.getVNInfoAt(OrigIdx);
if (!OVNI)
continue;
+
+ // Don't allow rematerialization immediately after the original def.
+ // It would be incorrect if OrigMI redefines the register.
+ // See PR14098.
+ if (SlotIndex::isSameInstr(OrigIdx, UseIdx))
+ return false;
+
if (OVNI != li.getVNInfoAt(UseIdx))
return false;
}