Changes in directory llvm/lib/Transforms/Scalar:
InstructionCombining.cpp updated: 1.618 -> 1.619
---
Log message:
Fix Transforms/InstCombine/2007-02-01-LoadSinkAlloca.ll, a serious code
pessimization where instcombine can sink a load (good for code size) that
prevents an alloca from being promoted by mem2reg (bad for everything).
---
Diffs of the changes: (+24 -0)
InstructionCombining.cpp | 24 ++++++++++++++++++++++++
1 files changed, 24 insertions(+)
Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.618
llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.619
--- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.618 Wed Jan 31
14:08:52 2007
+++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp Thu Feb 1 16:30:07 2007
@@ -7464,12 +7464,36 @@
/// of the block that defines it. This means that it must be obvious the value
/// of the load is not changed from the point of the load to the end of the
/// block it is in.
+///
+/// Finally, it is safe, but not profitable, to sink a load targetting a
+/// non-address-taken alloca. Doing so will cause us to not promote the alloca
+/// to a register.
static bool isSafeToSinkLoad(LoadInst *L) {
BasicBlock::iterator BBI = L, E = L->getParent()->end();
for (++BBI; BBI != E; ++BBI)
if (BBI->mayWriteToMemory())
return false;
+
+ // Check for non-address taken alloca. If not address-taken already, it
isn't
+ // profitable to do this xform.
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) {
+ bool isAddressTaken = false;
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
+ UI != E; ++UI) {
+ if (isa<LoadInst>(UI)) continue;
+ if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
+ // If storing TO the alloca, then the address isn't taken.
+ if (SI->getOperand(1) == AI) continue;
+ }
+ isAddressTaken = true;
+ break;
+ }
+
+ if (!isAddressTaken)
+ return false;
+ }
+
return true;
}
_______________________________________________
llvm-commits mailing list
llvm-commits@cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
