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| author | Jim Grosbach <grosbach@apple.com> | 2013-07-09 02:07:28 +0000 |
|---|---|---|
| committer | Jim Grosbach <grosbach@apple.com> | 2013-07-09 02:07:28 +0000 |
| commit | 842b1bdd940e365898581d6ff54794b8fa1a13c9 (patch) | |
| tree | bcc4c656f8a4eb5636e322109f54b9849a02a5ce /lib/Target/X86/X86ISelDAGToDAG.cpp | |
| parent | cc64dc66e740c0d78ecaca39c33c81b4062edd2e (diff) | |
| download | external_llvm-842b1bdd940e365898581d6ff54794b8fa1a13c9.zip external_llvm-842b1bdd940e365898581d6ff54794b8fa1a13c9.tar.gz external_llvm-842b1bdd940e365898581d6ff54794b8fa1a13c9.tar.bz2 | |
X86: Add comment.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185900 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/X86/X86ISelDAGToDAG.cpp')
| -rw-r--r-- | lib/Target/X86/X86ISelDAGToDAG.cpp | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp index b079281..9465420 100644 --- a/lib/Target/X86/X86ISelDAGToDAG.cpp +++ b/lib/Target/X86/X86ISelDAGToDAG.cpp @@ -2531,6 +2531,11 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) { // Prevent use of AH in a REX instruction by referencing AX instead. // Shift it down 8 bits. + // + // The current assumption of the register allocator is that isel + // won't generate explicit references to the GPR8_NOREX registers. If + // the allocator and/or the backend get enhanced to be more robust in + // that regard, this can be, and should be, removed. if (HiReg == X86::AH && Subtarget->is64Bit() && !SDValue(Node, 1).use_empty()) { SDValue Result = CurDAG->getCopyFromReg(CurDAG->getEntryNode(), dl, |