reames created this revision.
reames added reviewers: hfinkel, nlewycky, sanjoy.
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As the title says. Modelled after similar code in SCEV.
This is useful when analysing induction variables in loops which have been canonicalized by other passes. I wrote the tests as non-loops specifically to avoid the generality introduced in http://reviews.llvm.org/D17174. While that can handle many induction variables without *needing* to exploit nsw, there's no reason not to use it if we've already proven it.
http://reviews.llvm.org/D17177
Files:
lib/Analysis/LazyValueInfo.cpp
test/Transforms/CorrelatedValuePropagation/basic.ll
Index: test/Transforms/CorrelatedValuePropagation/basic.ll
===================================================================
--- test/Transforms/CorrelatedValuePropagation/basic.ll
+++ test/Transforms/CorrelatedValuePropagation/basic.ll
@@ -199,3 +199,58 @@
next:
ret void
}
+
+; Can we use nsw in LVI to prove lack of overflow?
+define i1 @add_nsw(i32 %s) {
+; CHECK-LABEL: @add_nsw(
+entry:
+ %cmp = icmp sgt i32 %s, 0
+ br i1 %cmp, label %positive, label %out
+
+positive:
+ %add = add nsw i32 %s, 1
+ %res = icmp sgt i32 %add, 0
+ br label %next
+next:
+; CHECK: next:
+; CHECK: ret i1 true
+ ret i1 %res
+out:
+ ret i1 false
+}
+
+define i1 @add_nsw2(i32 %s) {
+; CHECK-LABEL: @add_nsw2(
+entry:
+ %cmp = icmp sge i32 %s, 0
+ br i1 %cmp, label %positive, label %out
+
+positive:
+ %add = add nsw i32 %s, 1
+ %res = icmp ne i32 %add, 0
+ br label %next
+next:
+; CHECK: next:
+; CHECK: ret i1 true
+ ret i1 %res
+out:
+ ret i1 false
+}
+
+define i1 @add_nuw(i32 %s) {
+; CHECK-LABEL: @add_nuw(
+entry:
+ %cmp = icmp ult i32 %s, 400
+ br i1 %cmp, label %positive, label %out
+
+positive:
+ %add = add nsw i32 %s, 1
+ %res = icmp ne i32 %add, -100
+ br label %next
+next:
+; CHECK: next:
+; CHECK: ret i1 true
+ ret i1 %res
+out:
+ ret i1 false
+}
Index: lib/Analysis/LazyValueInfo.cpp
===================================================================
--- lib/Analysis/LazyValueInfo.cpp
+++ lib/Analysis/LazyValueInfo.cpp
@@ -961,6 +961,27 @@
if (isa<BinaryOperator>(BBI)) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
RHSRange = ConstantRange(RHS->getValue());
+
+ // Try to use information about wrap flags to refine the range LHS can
+ // legally have. This is a slightly weird way to implement forward
+ // propagation over overflowing instructions, but it seems to be the only
+ // clean one we have. NOTE: Because we may have speculated the
+ // instruction, we can't constrain other uses of LHS even if they would
+ // seem to be equivelent control dependent with this op.
+ if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(BBI)) {
+ unsigned WrapKind = 0;
+ if (OBO->hasNoSignedWrap())
+ WrapKind |= OverflowingBinaryOperator::NoSignedWrap;
+ if (OBO->hasNoUnsignedWrap())
+ WrapKind |= OverflowingBinaryOperator::NoUnsignedWrap;
+
+ if (WrapKind) {
+ auto OpCode = static_cast<Instruction::BinaryOps>(BBI->getOpcode());
+ auto NoWrapCR =
+ ConstantRange::makeNoWrapRegion(OpCode, RHS->getValue(), WrapKind);
+ LHSRange = LHSRange.intersectWith(NoWrapCR);
+ }
+ }
} else {
BBLV.markOverdefined();
return true;
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