[PATCH] D156845: [ConstantRange] Calculate precise range for shl by -1

[Allen zhong via Phabricator via llvm-commits]

Allen updated this revision to Diff 548847.
Allen added a comment.

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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D156845/new/

https://reviews.llvm.org/D156845

Files:
  llvm/lib/IR/ConstantRange.cpp
  llvm/test/Transforms/FunctionSpecialization/and-add-shl.ll


Index: llvm/test/Transforms/FunctionSpecialization/and-add-shl.ll
===================================================================
--- llvm/test/Transforms/FunctionSpecialization/and-add-shl.ll
+++ llvm/test/Transforms/FunctionSpecialization/and-add-shl.ll
@@ -30,8 +30,7 @@
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[OP1_P2]])
 ; CHECK-NEXT:    [[SHIFT:%.*]] = shl nsw i8 -1, [[X]]
 ; CHECK-NEXT:    [[NOT:%.*]] = xor i8 [[SHIFT]], -1
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[NOT]], 32
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 0
 ;
   %op1_p2 = icmp ule i8 %x, 5
   call void @llvm.assume(i1 %op1_p2)
@@ -48,8 +47,7 @@
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[OP1_P2]])
 ; CHECK-NEXT:    [[SHIFT:%.*]] = shl nsw i8 -1, [[X]]
 ; CHECK-NEXT:    [[NOT:%.*]] = xor i8 [[SHIFT]], -1
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[NOT]], 48
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 0
 ;
   %op1_p2 = icmp ule i8 %x, 4
   call void @llvm.assume(i1 %op1_p2)
Index: llvm/lib/IR/ConstantRange.cpp
===================================================================
--- llvm/lib/IR/ConstantRange.cpp
+++ llvm/lib/IR/ConstantRange.cpp
@@ -1478,6 +1478,14 @@
 
   APInt OtherMax = Other.getUnsignedMax();
 
+  bool Neg = false;
+  if (getSingleElement() && isAllNegative()) {
+    // Negative the number to easily calculate its shifted value.
+    Neg = true;
+    Min = -Min;
+    Max = -Max;
+  }
+
   // There's overflow!
   if (OtherMax.ugt(Max.countl_zero()))
     return getFull();
@@ -1487,6 +1495,14 @@
   Min <<= Other.getUnsignedMin();
   Max <<= OtherMax;
 
+  if (Neg) {
+    // For negitive value c, its shifted range is [-((-c) <<Other.max) , -((-c)
+    // <<Other.min)]
+    Min = -Min;
+    Max = -Max;
+    return ConstantRange::getNonEmpty(std::move(Max), std::move(Min) + 1);
+  }
+  // For positive value c, its shifted range is [c <<Other.min , c <<Other.max]
   return ConstantRange::getNonEmpty(std::move(Min), std::move(Max) + 1);
 }
 


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