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authorNuno Lopes <nunoplopes@sapo.pt>2012-07-03 17:30:18 +0000
committerNuno Lopes <nunoplopes@sapo.pt>2012-07-03 17:30:18 +0000
commit42d80c7a5b369285c10c0dc4b2e025f7a65d635e (patch)
treee220c91a009529fa7d2192da7e6d959c1c135dea
parent0dff532fce434c3e9fdf9695aed8efeb5f752ed5 (diff)
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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
-rw-r--r--lib/Transforms/Scalar/BoundsChecking.cpp17
-rw-r--r--test/Transforms/BoundsChecking/phi.ll8
2 files changed, 16 insertions, 9 deletions
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 @@ namespace {
}
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 @@ bool BoundsChecking::instrument(Value *Ptr, Value *InstVal) {
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 @@ bool BoundsChecking::instrument(Value *Ptr, Value *InstVal) {
// . 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;
diff --git a/test/Transforms/BoundsChecking/phi.ll b/test/Transforms/BoundsChecking/phi.ll
index 6c42ec8..86b5922 100644
--- a/test/Transforms/BoundsChecking/phi.ll
+++ b/test/Transforms/BoundsChecking/phi.ll
@@ -34,10 +34,14 @@ while.body.i.preheader:
while.body.i:
; CHECK: phi
; CHECK-NEXT: phi
-; CHECK-NEXT: phi
-; CHECK: trap
+; CHECK-NOT: phi
%c.addr.02.i = phi i8* [ %incdec.ptr.i, %while.body.i ], [ %addr, %while.body.i.preheader ]
%incdec.ptr.i = getelementptr inbounds i8* %c.addr.02.i, i64 -1
+; CHECK: sub i64 10, %0
+; CHECK-NEXT: icmp ult i64 10, %0
+; CHECK-NEXT: icmp ult i64 {{.*}}, 1
+; CHECK-NEXT: or i1
+; CHECK-NEXT: br {{.*}}, label %trap
store i8 100, i8* %c.addr.02.i, align 1
%0 = load i8* %incdec.ptr.i, align 1
%tobool.i = icmp eq i8 %0, 0