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[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
This commit is contained in:
Andrea Di Biagio 2016-09-26 12:07:23 +00:00
parent c4ec11f451
commit a82d52d11d
2 changed files with 28 additions and 10 deletions
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23
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -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));
Value *ShiftLeft;
if (!match(Op1, m_ZExt(m_Value(ShiftLeft))))
ShiftLeft = Op1;
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());
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();

15
llvm/test/Transforms/InstCombine/udiv-simplify.ll
View File

@ -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
}