[InstCombine] Teach the udiv folding logic how to handle constant expressions.

This patch fixes PR30366.

Function foldUDivShl() worked under the assumption that one of the values
in input to the function was always an instance of llvm::Instruction.
However, function visitUDivOperand() (the only user of foldUDivShl) was
clearly violating that precondition; internally, visitUDivOperand() uses pattern
matches to check the operands of a udiv. Pattern matchers for binary operators
know how to handle both Instruction and ConstantExpr values.

This patch fixes the problem in foldUDivShl(). Now we use pattern matchers
instead of explicit casts to Instruction. The reduced test case from PR30366
has been added to test file InstCombine/udiv-simplify.ll.

Differential Revision: https://reviews.llvm.org/D24565

llvm-svn: 282398

1 files changed, 14 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index cd31c63ff28..e1e3cbc5195 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -991,19 +991,22 @@ static Instruction *foldUDivNegCst(Value *Op0, Value *Op1,
 }
 
 // X udiv (C1 << N), where C1 is "1<<C2"  -->  X >> (N+C2)
+// X udiv (zext (C1 << N)), where C1 is "1<<C2"  -->  X >> (N+C2)
 static Instruction *foldUDivShl(Value *Op0, Value *Op1, const BinaryOperator &I,
                                 InstCombiner &IC) {
-  Instruction *ShiftLeft = cast<Instruction>(Op1);
-  if (isa<ZExtInst>(ShiftLeft))
-    ShiftLeft = cast<Instruction>(ShiftLeft->getOperand(0));
-
-  const APInt &CI =
-      cast<Constant>(ShiftLeft->getOperand(0))->getUniqueInteger();
-  Value *N = ShiftLeft->getOperand(1);
-  if (CI != 1)
-    N = IC.Builder->CreateAdd(N, ConstantInt::get(N->getType(), CI.logBase2()));
-  if (ZExtInst *Z = dyn_cast<ZExtInst>(Op1))
-    N = IC.Builder->CreateZExt(N, Z->getDestTy());
+  Value *ShiftLeft;
+  if (!match(Op1, m_ZExt(m_Value(ShiftLeft))))
+    ShiftLeft = Op1;
+
+  const APInt *CI;
+  Value *N;
+  if (!match(ShiftLeft, m_Shl(m_APInt(CI), m_Value(N))))
+    llvm_unreachable("match should never fail here!");
+  if (*CI != 1)
+    N = IC.Builder->CreateAdd(N,
+                              ConstantInt::get(N->getType(), CI->logBase2()));
+  if (Op1 != ShiftLeft)
+    N = IC.Builder->CreateZExt(N, Op1->getType());
   BinaryOperator *LShr = BinaryOperator::CreateLShr(Op0, N);
   if (I.isExact())
     LShr->setIsExact();