[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
Chris Lattner
lattner at cs.uiuc.edu
Tue Sep 12 23:02:56 PDT 2006
Changes in directory llvm/lib/CodeGen/SelectionDAG:
SelectionDAGISel.cpp updated: 1.275 -> 1.276
---
Log message:
If LSR went through a lot of trouble to put constants (e.g. the addr of a global
in a specific BB, don't undo this!). This allows us to compile
CodeGen/X86/loop-hoist.ll into:
_foo:
xorl %eax, %eax
*** movl L_Arr$non_lazy_ptr, %ecx
movl 4(%esp), %edx
LBB1_1: #cond_true
movl %eax, (%ecx,%eax,4)
incl %eax
cmpl %edx, %eax
jne LBB1_1 #cond_true
LBB1_2: #return
ret
instead of:
_foo:
xorl %eax, %eax
movl 4(%esp), %ecx
LBB1_1: #cond_true
*** movl L_Arr$non_lazy_ptr, %edx
movl %eax, (%edx,%eax,4)
incl %eax
cmpl %ecx, %eax
jne LBB1_1 #cond_true
LBB1_2: #return
ret
This was noticed in 464.h264ref. This doesn't usually affect PPC,
but strikes X86 all the time.
---
Diffs of the changes: (+9 -0)
SelectionDAGISel.cpp | 9 +++++++++
1 files changed, 9 insertions(+)
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1.275 llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1.276
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1.275 Sun Sep 10 01:36:57 2006
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp Wed Sep 13 01:02:42 2006
@@ -3234,6 +3234,15 @@
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
MadeChange |= OptimizeGEPExpression(GEPI, TLI.getTargetData());
} else if (CastInst *CI = dyn_cast<CastInst>(I)) {
+ // If the source of the cast is a constant, then this should have
+ // already been constant folded. The only reason NOT to constant fold
+ // it is if something (e.g. LSR) was careful to place the constant
+ // evaluation in a block other than then one that uses it (e.g. to hoist
+ // the address of globals out of a loop). If this is the case, we don't
+ // want to forward-subst the cast.
+ if (isa<Constant>(CI->getOperand(0)))
+ continue;
+
// If this is a noop copy, sink it into user blocks to reduce the number
// of virtual registers that must be created and coallesced.
MVT::ValueType SrcVT = TLI.getValueType(CI->getOperand(0)->getType());
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