[ConstantRange] Support subtraction in makeGuaranteedNoWrapRegion.

Previously ConstantRange::makeGuaranteedNoWrapRegion only handled addition.  This adds support for subtraction.

Differential Revision: https://reviews.llvm.org/D40036

llvm-svn: 319806

1 files changed, 52 insertions, 28 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 4bd17257016..77ecd7a9077 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -199,39 +199,63 @@ ConstantRange::makeGuaranteedNoWrapRegion(Instruction::BinaryOps BinOp,
          "NoWrapKind invalid!");
 
   unsigned BitWidth = Other.getBitWidth();
-  if (BinOp != Instruction::Add)
+  ConstantRange Result(BitWidth);
+
+  switch (BinOp) {
+  default:
     // Conservative answer: empty set
     return ConstantRange(BitWidth, false);
 
-  if (auto *C = Other.getSingleElement())
-    if (C->isNullValue())
-      // Full set: nothing signed / unsigned wraps when added to 0.
-      return ConstantRange(BitWidth);
-
-  ConstantRange Result(BitWidth);
+  case Instruction::Add:
+    if (auto *C = Other.getSingleElement())
+      if (C->isNullValue())
+        // Full set: nothing signed / unsigned wraps when added to 0.
+        return ConstantRange(BitWidth);
+    if (NoWrapKind & OBO::NoUnsignedWrap)
+      Result =
+          SubsetIntersect(Result, ConstantRange(APInt::getNullValue(BitWidth),
+                                                -Other.getUnsignedMax()));
+    if (NoWrapKind & OBO::NoSignedWrap) {
+      const APInt &SignedMin = Other.getSignedMin();
+      const APInt &SignedMax = Other.getSignedMax();
+      if (SignedMax.isStrictlyPositive())
+        Result = SubsetIntersect(
+            Result,
+            ConstantRange(APInt::getSignedMinValue(BitWidth),
+                          APInt::getSignedMinValue(BitWidth) - SignedMax));
+      if (SignedMin.isNegative())
+        Result = SubsetIntersect(
+            Result,
+            ConstantRange(APInt::getSignedMinValue(BitWidth) - SignedMin,
+                          APInt::getSignedMinValue(BitWidth)));
+    }
+    return Result;
 
-  if (NoWrapKind & OBO::NoUnsignedWrap)
-    Result =
-        SubsetIntersect(Result, ConstantRange(APInt::getNullValue(BitWidth),
-                                              -Other.getUnsignedMax()));
-
-  if (NoWrapKind & OBO::NoSignedWrap) {
-    const APInt &SignedMin = Other.getSignedMin();
-    const APInt &SignedMax = Other.getSignedMax();
-
-    if (SignedMax.isStrictlyPositive())
-      Result = SubsetIntersect(
-          Result,
-          ConstantRange(APInt::getSignedMinValue(BitWidth),
-                        APInt::getSignedMinValue(BitWidth) - SignedMax));
-
-    if (SignedMin.isNegative())
-      Result = SubsetIntersect(
-          Result, ConstantRange(APInt::getSignedMinValue(BitWidth) - SignedMin,
-                                APInt::getSignedMinValue(BitWidth)));
+  case Instruction::Sub:
+    if (auto *C = Other.getSingleElement())
+      if (C->isNullValue())
+        // Full set: nothing signed / unsigned wraps when subtracting 0.
+        return ConstantRange(BitWidth);
+    if (NoWrapKind & OBO::NoUnsignedWrap)
+      Result =
+          SubsetIntersect(Result, ConstantRange(Other.getUnsignedMax(),
+                                                APInt::getMinValue(BitWidth)));
+    if (NoWrapKind & OBO::NoSignedWrap) {
+      const APInt &SignedMin = Other.getSignedMin();
+      const APInt &SignedMax = Other.getSignedMax();
+      if (SignedMax.isStrictlyPositive())
+        Result = SubsetIntersect(
+            Result,
+            ConstantRange(APInt::getSignedMinValue(BitWidth) + SignedMax,
+                          APInt::getSignedMinValue(BitWidth)));
+      if (SignedMin.isNegative())
+        Result = SubsetIntersect(
+            Result,
+            ConstantRange(APInt::getSignedMinValue(BitWidth),
+                          APInt::getSignedMinValue(BitWidth) + SignedMin));
+    }
+    return Result;
   }
-
-  return Result;
 }
 
 bool ConstantRange::isFullSet() const {