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 0dfb084f1e15bd6f467f11ca82ee46a860c05d2f..f8fbc7ddf0c1e35c0ca748a725c0a6543e9e8295 100644 (file)
--- a/lib/CodeGen/LiveRangeEdit.cpp
+++ b/lib/CodeGen/LiveRangeEdit.cpp
@@ -96,6 +96,13 @@ bool LiveRangeEdit::allUsesAvailableAt(const MachineInstr *OrigMI,
     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;
   }

diff --git a/test/CodeGen/X86/pr14098.ll b/test/CodeGen/X86/pr14098.ll
new file mode 100644 (file)
index 0000000..6ce2449
--- /dev/null
+++ b/test/CodeGen/X86/pr14098.ll
@@ -0,0 +1,23 @@
+; RUN: llc -mtriple i386-unknown-linux-gnu -relocation-model=pic -verify-machineinstrs < %s
+; We used to crash on this.
+
+declare void @foo()
+declare void @foo3(i1 %x)
+define void @bar(i1 %a1, i16 %a2) nounwind align 2 {
+bb0:
+  %a3 = trunc i16 %a2 to i8
+  %a4 = lshr i16 %a2, 8
+  %a5 = trunc i16 %a4 to i8
+  br i1 %a1, label %bb1, label %bb2
+bb1:
+  br label %bb2
+bb2:
+  %a6 = phi i8 [ 3, %bb0 ], [ %a5, %bb1 ]
+  %a7 = phi i8 [ 9, %bb0 ], [ %a3, %bb1 ]
+  %a8 = icmp eq i8 %a6, 1
+  call void @foo()
+  %a9 = icmp eq i8 %a7, 0
+  call void @foo3(i1 %a9)
+  call void @foo3(i1 %a8)
+  ret void
+}