[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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282398 91177308-0d34-0410-b5e6-96231b3b80d8

Author: adibiagio

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();

test/Transforms/InstCombine/udiv-simplify.ll

@@ -47,3 +47,18 @@ define i64 @test2_PR2274(i32 %x, i32 %v) nounwind {
   %z = sext i32 %r to i64
   ret i64 %z
 }
+
+; The udiv should be simplified according to the rule:
+; X udiv (C1 << N), where C1 is `1<<C2` --> X >> (N+C2)
+@b = external global [1 x i16]
+
+define i32 @PR30366(i1 %a) {
+; CHECK-LABEL: @PR30366(
+; CHECK-NEXT:    [[Z:%.*]] = zext i1 %a to i32
+; CHECK-NEXT:    [[D:%.*]] = lshr i32 [[Z]], zext (i16 ptrtoint ([1 x i16]* @b to i16) to i32)
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %z = zext i1 %a to i32
+  %d = udiv i32 %z, zext (i16 shl (i16 1, i16 ptrtoint ([1 x i16]* @b to i16)) to i32)
+  ret i32 %d
+}