[llvm] r213447 - Make Value::isDereferenceablePointer handle offsets to pointer types with dereferenceable attributes
Hal Finkel
hfinkel at anl.gov
Fri Jul 18 20:25:16 PDT 2014
Author: hfinkel
Date: Fri Jul 18 22:25:16 2014
New Revision: 213447
URL: http://llvm.org/viewvc/llvm-project?rev=213447&view=rev
Log:
Make Value::isDereferenceablePointer handle offsets to pointer types with dereferenceable attributes
When we have a parameter (or call site return) with a dereferenceable
attribute, it can specify the size of an array pointed to by that parameter. If
we have a value for which we can accumulate a constant offset to such a
parameter, then we can use that offset in a direct comparison with the size
specified by the dereferenceable attribute.
This enables us to handle cases like this:
int foo(int a[static 3]) {
return a[2]; /* this is always dereferenceable */
}
Modified:
llvm/trunk/lib/IR/Value.cpp
llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll
Modified: llvm/trunk/lib/IR/Value.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Value.cpp?rev=213447&r1=213446&r2=213447&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Value.cpp (original)
+++ llvm/trunk/lib/IR/Value.cpp Fri Jul 18 22:25:16 2014
@@ -574,6 +574,27 @@ static bool isDereferenceablePointer(con
/// isDereferenceablePointer - Test if this value is always a pointer to
/// allocated and suitably aligned memory for a simple load or store.
bool Value::isDereferenceablePointer(const DataLayout *DL) const {
+ // When dereferenceability information is provided by a dereferenceable
+ // attribute, we know exactly how many bytes are dereferenceable. If we can
+ // determine the exact offset to the attributed variable, we can use that
+ // information here.
+ Type *Ty = getType()->getPointerElementType();
+ if (Ty->isSized() && DL) {
+ APInt Offset(DL->getTypeStoreSizeInBits(getType()), 0);
+ const Value *BV = stripAndAccumulateInBoundsConstantOffsets(*DL, Offset);
+
+ APInt DerefBytes(Offset.getBitWidth(), 0);
+ if (const Argument *A = dyn_cast<Argument>(BV))
+ DerefBytes = A->getDereferenceableBytes();
+ else if (ImmutableCallSite CS = BV)
+ DerefBytes = CS.getDereferenceableBytes(0);
+
+ if (DerefBytes.getBoolValue() && Offset.isNonNegative()) {
+ if (DerefBytes.uge(Offset + DL->getTypeStoreSize(Ty)))
+ return true;
+ }
+ }
+
SmallPtrSet<const Value *, 32> Visited;
return ::isDereferenceablePointer(this, DL, Visited);
}
Modified: llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll?rev=213447&r1=213446&r2=213447&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll (original)
+++ llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll Fri Jul 18 22:25:16 2014
@@ -82,5 +82,87 @@ for.end:
ret void
}
+; This test represents the following function:
+; void test3(int * restrict a, int * restrict b, int c[static 3], int n) {
+; for (int i = 0; i < n; ++i)
+; if (a[i] > 0)
+; a[i] = c[2]*b[i];
+; }
+; and we want to hoist the load of c[2] out of the loop. This can be done only
+; because the dereferenceable attribute is on %c.
+
+; CHECK-LABEL: @test3
+; CHECK: load i32* %c2, align 4
+; CHECK: for.body:
+
+define void @test3(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32* nocapture readonly dereferenceable(12) %c, i32 %n) #0 {
+entry:
+ %cmp11 = icmp sgt i32 %n, 0
+ br i1 %cmp11, label %for.body, label %for.end
+
+for.body: ; preds = %entry, %for.inc
+ %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+ %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
+ %0 = load i32* %arrayidx, align 4
+ %cmp1 = icmp sgt i32 %0, 0
+ br i1 %cmp1, label %if.then, label %for.inc
+
+if.then: ; preds = %for.body
+ %c2 = getelementptr inbounds i32* %c, i64 2
+ %1 = load i32* %c2, align 4
+ %arrayidx3 = getelementptr inbounds i32* %b, i64 %indvars.iv
+ %2 = load i32* %arrayidx3, align 4
+ %mul = mul nsw i32 %2, %1
+ store i32 %mul, i32* %arrayidx, align 4
+ br label %for.inc
+
+for.inc: ; preds = %for.body, %if.then
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+ %exitcond = icmp eq i32 %lftr.wideiv, %n
+ br i1 %exitcond, label %for.end, label %for.body
+
+for.end: ; preds = %for.inc, %entry
+ ret void
+}
+
+; This is the same as @test3, but with a dereferenceable attribute on %c with a
+; size too small to cover c[2] (and so we should not hoist it).
+
+; CHECK-LABEL: @test4
+; CHECK: if.then:
+; CHECK: load i32* %c2, align 4
+
+define void @test4(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32* nocapture readonly dereferenceable(11) %c, i32 %n) #0 {
+entry:
+ %cmp11 = icmp sgt i32 %n, 0
+ br i1 %cmp11, label %for.body, label %for.end
+
+for.body: ; preds = %entry, %for.inc
+ %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+ %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
+ %0 = load i32* %arrayidx, align 4
+ %cmp1 = icmp sgt i32 %0, 0
+ br i1 %cmp1, label %if.then, label %for.inc
+
+if.then: ; preds = %for.body
+ %c2 = getelementptr inbounds i32* %c, i64 2
+ %1 = load i32* %c2, align 4
+ %arrayidx3 = getelementptr inbounds i32* %b, i64 %indvars.iv
+ %2 = load i32* %arrayidx3, align 4
+ %mul = mul nsw i32 %2, %1
+ store i32 %mul, i32* %arrayidx, align 4
+ br label %for.inc
+
+for.inc: ; preds = %for.body, %if.then
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+ %exitcond = icmp eq i32 %lftr.wideiv, %n
+ br i1 %exitcond, label %for.end, label %for.body
+
+for.end: ; preds = %for.inc, %entry
+ ret void
+}
+
attributes #0 = { nounwind uwtable }
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