[PATCH] D17177: [LVI] Exploit nsw/nuw when computing constant ranges

[Philip Reames via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL260705: [LVI] Exploit nsw/nuw when computing constant ranges (authored by reames).

Changed prior to commit:
  http://reviews.llvm.org/D17177?vs=47748&id=47821#toc

Repository:
  rL LLVM

http://reviews.llvm.org/D17177

Files:
  llvm/trunk/lib/Analysis/LazyValueInfo.cpp
  llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll

Index: llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll
===================================================================
--- llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll
+++ llvm/trunk/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: llvm/trunk/lib/Analysis/LazyValueInfo.cpp
===================================================================
--- llvm/trunk/lib/Analysis/LazyValueInfo.cpp
+++ llvm/trunk/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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