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authorManman Ren <mren@apple.com>2012-08-07 06:16:46 +0000
committerManman Ren <mren@apple.com>2012-08-07 06:16:46 +0000
commitba86b13ad9cd6a9707a954598863da1e2a9f773b (patch)
tree482ffd2aed786cddf7cce28e96075c7915155911 /lib
parentcbfce4557751acef4e7970d6e4b9583ced7e0e93 (diff)
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MachineCSE: Update the heuristics for isProfitableToCSE.
If the result of a common subexpression is used at all uses of the candidate expression, CSE should not increase the live range of the common subexpression. rdar://11393714 and rdar://11819721 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161396 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r--lib/CodeGen/MachineCSE.cpp23
1 files changed, 23 insertions, 0 deletions
diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp
index 9cfe9ab..0a76f8d 100644
--- a/lib/CodeGen/MachineCSE.cpp
+++ b/lib/CodeGen/MachineCSE.cpp
@@ -324,6 +324,29 @@ bool MachineCSE::isProfitableToCSE(unsigned CSReg, unsigned Reg,
MachineInstr *CSMI, MachineInstr *MI) {
// FIXME: Heuristics that works around the lack the live range splitting.
+ // If CSReg is used at all uses of Reg, CSE should not increase register
+ // pressure of CSReg.
+ bool MayIncreasePressure = true;
+ if (TargetRegisterInfo::isVirtualRegister(CSReg) &&
+ TargetRegisterInfo::isVirtualRegister(Reg)) {
+ MayIncreasePressure = false;
+ SmallPtrSet<MachineInstr*, 8> CSUses;
+ for (MachineRegisterInfo::use_nodbg_iterator I =MRI->use_nodbg_begin(CSReg),
+ E = MRI->use_nodbg_end(); I != E; ++I) {
+ MachineInstr *Use = &*I;
+ CSUses.insert(Use);
+ }
+ for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(Reg),
+ E = MRI->use_nodbg_end(); I != E; ++I) {
+ MachineInstr *Use = &*I;
+ if (!CSUses.count(Use)) {
+ MayIncreasePressure = true;
+ break;
+ }
+ }
+ }
+ if (!MayIncreasePressure) return true;
+
// Heuristics #1: Don't CSE "cheap" computation if the def is not local or in
// an immediate predecessor. We don't want to increase register pressure and
// end up causing other computation to be spilled.