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[InstCombine] Teach ComputeNumSignBitsImpl to handle integer multiply instruction.

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Differential Revision: https://reviews.llvm.org/D36679


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311206 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Amjad Aboud 2017-08-18 22:56:55 +00:00
parent de4770b949
commit 066b24cb94
2 changed files with 26 additions and 0 deletions
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11
lib/Analysis/ValueTracking.cpp
View File

@ -2196,6 +2196,17 @@ static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
if (Tmp == 1) return 1; // Early out.
return std::min(Tmp, Tmp2)-1;
case Instruction::Mul: {
// The output of the Mul can be at most twice the valid bits in the inputs.
unsigned SignBitsOp0 = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
if (SignBitsOp0 == 1) return 1; // Early out.
unsigned SignBitsOp1 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (SignBitsOp1 == 1) return 1;
unsigned OutValidBits =
(TyBits - SignBitsOp0 + 1) + (TyBits - SignBitsOp1 + 1);
return OutValidBits > TyBits ? 1 : TyBits - OutValidBits + 1;
}
case Instruction::PHI: {
const PHINode *PN = cast<PHINode>(U);
unsigned NumIncomingValues = PN->getNumIncomingValues();

15
test/Transforms/InstCombine/trunc.ll
View File

@ -89,6 +89,21 @@ define i32 @test6(i64 %A) {
ret i32 %D
}
define i16 @ashr_mul(i8 %X, i8 %Y) {
; CHECK-LABEL: @ashr_mul(
; CHECK-NEXT: [[A:%.*]] = sext i8 %X to i16
; CHECK-NEXT: [[B:%.*]] = sext i8 %Y to i16
; CHECK-NEXT: [[C:%.*]] = mul nsw i16 [[A]], [[B]]
; CHECK-NEXT: [[D:%.*]] = ashr i16 [[C]], 8
; CHECK-NEXT: ret i16 [[D]]
%A = sext i8 %X to i20
%B = sext i8 %Y to i20
%C = mul i20 %A, %B
%D = ashr i20 %C, 8
%E = trunc i20 %D to i16
ret i16 %E
}
define i32 @trunc_ashr(i32 %X) {
; CHECK-LABEL: @trunc_ashr(
; CHECK-NEXT: [[B:%.*]] = or i32 [[X:%.*]], -2147483648