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Avoid rematerializing a redef immediately after the old def.

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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
This commit is contained in:
Jakob Stoklund Olesen 2012-10-16 22:51:58 +00:00
parent cdcdfd2cab
commit 320db3f805
2 changed files with 30 additions and 0 deletions
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7
lib/CodeGen/LiveRangeEdit.cpp
View File

@ -96,6 +96,13 @@ bool LiveRangeEdit::allUsesAvailableAt(const MachineInstr *OrigMI,
const VNInfo *OVNI = li.getVNInfoAt(OrigIdx); const VNInfo *OVNI = li.getVNInfoAt(OrigIdx);
if (!OVNI) if (!OVNI)
continue; 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)) if (OVNI != li.getVNInfoAt(UseIdx))
return false; return false;
} }

23
test/CodeGen/X86/pr14098.ll Normal file
View File

@ -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
}