BoundsChecking: optimize out the check for offset < 0 if size is known to be >= 0 (signed).
(LLVM optimizers cannot do this optimization by themselves)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159668 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/BoundsChecking.cpp b/lib/Transforms/Scalar/BoundsChecking.cpp
index 0690d76..ef2f39d 100644
--- a/lib/Transforms/Scalar/BoundsChecking.cpp
+++ b/lib/Transforms/Scalar/BoundsChecking.cpp
@@ -67,11 +67,8 @@
}
char BoundsChecking::ID = 0;
-INITIALIZE_PASS_BEGIN(BoundsChecking, "bounds-checking",
- "Run-time bounds checking", false, false)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
-INITIALIZE_PASS_END(BoundsChecking, "bounds-checking",
- "Run-time bounds checking", false, false)
+INITIALIZE_PASS(BoundsChecking, "bounds-checking", "Run-time bounds checking",
+ false, false)
/// getTrapBB - create a basic block that traps. All overflowing conditions
@@ -141,6 +138,7 @@
Value *Size = SizeOffset.first;
Value *Offset = SizeOffset.second;
+ ConstantInt *SizeCI = dyn_cast<ConstantInt>(Size);
IntegerType *IntTy = TD->getIntPtrType(Inst->getContext());
Value *NeededSizeVal = ConstantInt::get(IntTy, NeededSize);
@@ -149,12 +147,17 @@
// . Offset >= 0 (since the offset is given from the base ptr)
// . Size >= Offset (unsigned)
// . Size - Offset >= NeededSize (unsigned)
+ //
+ // optimization: if Size >= 0 (signed), skip 1st check
// FIXME: add NSW/NUW here? -- we dont care if the subtraction overflows
Value *ObjSize = Builder->CreateSub(Size, Offset);
- Value *Cmp1 = Builder->CreateICmpSLT(Offset, ConstantInt::get(IntTy, 0));
Value *Cmp2 = Builder->CreateICmpULT(Size, Offset);
Value *Cmp3 = Builder->CreateICmpULT(ObjSize, NeededSizeVal);
- Value *Or = Builder->CreateOr(Cmp1, Builder->CreateOr(Cmp2, Cmp3));
+ Value *Or = Builder->CreateOr(Cmp2, Cmp3);
+ if (!SizeCI || SizeCI->getValue().slt(0)) {
+ Value *Cmp1 = Builder->CreateICmpSLT(Offset, ConstantInt::get(IntTy, 0));
+ Or = Builder->CreateOr(Cmp1, Or);
+ }
emitBranchToTrap(Or);
++ChecksAdded;