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[InstCombine] extend rotate-left-by-constant canonicalization to funnel shift 

Follow-up to:
rL356338

Rotates are a special case of funnel shift where the 2 input operands
are the same value, but that does not need to be a restriction for the
canonicalization when the shift amount is a constant.

llvm-svn: 356369
This commit is contained in:
Sanjay Patel 2019-03-18 14:10:11 +00:00
parent f9ab4f5f4e
commit 84de8a30a0
2 changed files with 15 additions and 14 deletions
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19
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -2006,28 +2006,29 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
II->setArgOperand(2, ModuloC);
return II;
}
// Canonicalize rotate right by constant to rotate left. This is not
// entirely arbitrary. For historical reasons, the backend may recognize
// rotate left patterns but miss rotate right patterns.
if (II->getIntrinsicID() == Intrinsic::fshr && Op0 == Op1) {
// fshr X, X, C --> fshl X, X, (BitWidth - C)
// Canonicalize funnel shift right by constant to funnel shift left. This
// is not entirely arbitrary. For historical reasons, the backend may
// recognize rotate left patterns but miss rotate right patterns.
if (II->getIntrinsicID() == Intrinsic::fshr) {
// fshr X, Y, C --> fshl X, Y, (BitWidth - C)
assert(ConstantExpr::getICmp(ICmpInst::ICMP_UGT, WidthC, ShAmtC) ==
ConstantInt::getTrue(CmpInst::makeCmpResultType(Ty)) &&
"Shift amount expected to be modulo bitwidth");
Constant *LeftShiftC = ConstantExpr::getSub(WidthC, ShAmtC);
Module *Mod = II->getModule();
Function *Fshl = Intrinsic::getDeclaration(Mod, Intrinsic::fshl, Ty);
return CallInst::Create(Fshl, { Op0, Op0, LeftShiftC });
return CallInst::Create(Fshl, { Op0, Op1, LeftShiftC });
}
}
// TODO: Pull this into the block above. We can handle semi-arbitrary vector
// shift amount constants as well as splats.
const APInt *SA;
if (match(II->getArgOperand(2), m_APInt(SA))) {
uint64_t ShiftAmt = SA->urem(BitWidth);
assert(ShiftAmt != 0 && "SimplifyCall should have handled zero shift");
// Normalize to funnel shift left.
if (II->getIntrinsicID() == Intrinsic::fshr)
ShiftAmt = BitWidth - ShiftAmt;
assert(II->getIntrinsicID() == Intrinsic::fshl &&
"All funnel shifts by simple constants should go left");
// fshl(X, 0, C) -> shl X, C
// fshl(X, undef, C) -> shl X, C

10
llvm/test/Transforms/InstCombine/fsh.ll
View File

@ -271,7 +271,7 @@ define <2 x i31> @fshl_op1_undef_vec(<2 x i31> %x) {
define <2 x i32> @fshr_op0_undef_vec(<2 x i32> %x) {
; CHECK-LABEL: @fshr_op0_undef_vec(
; CHECK-NEXT: [[R:%.*]] = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> undef, <2 x i32> [[X:%.*]], <2 x i32> <i32 31, i32 1>)
; CHECK-NEXT: [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> undef, <2 x i32> [[X:%.*]], <2 x i32> <i32 1, i32 31>)
; CHECK-NEXT: ret <2 x i32> [[R]]
;
%r = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> undef, <2 x i32> %x, <2 x i32> <i32 -1, i32 33>)
@ -280,7 +280,7 @@ define <2 x i32> @fshr_op0_undef_vec(<2 x i32> %x) {
define <2 x i32> @fshr_op1_zero_vec(<2 x i32> %x) {
; CHECK-LABEL: @fshr_op1_zero_vec(
; CHECK-NEXT: [[R:%.*]] = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> [[X:%.*]], <2 x i32> zeroinitializer, <2 x i32> <i32 31, i32 1>)
; CHECK-NEXT: [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> zeroinitializer, <2 x i32> <i32 1, i32 31>)
; CHECK-NEXT: ret <2 x i32> [[R]]
;
%r = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> %x, <2 x i32> zeroinitializer, <2 x i32> <i32 -1, i32 33>)
@ -355,7 +355,7 @@ define i32 @fshl_constant_shift_amount_modulo_bitwidth(i32 %x, i32 %y) {
define i33 @fshr_constant_shift_amount_modulo_bitwidth(i33 %x, i33 %y) {
; CHECK-LABEL: @fshr_constant_shift_amount_modulo_bitwidth(
; CHECK-NEXT: [[R:%.*]] = call i33 @llvm.fshr.i33(i33 [[X:%.*]], i33 [[Y:%.*]], i33 1)
; CHECK-NEXT: [[R:%.*]] = call i33 @llvm.fshl.i33(i33 [[X:%.*]], i33 [[Y:%.*]], i33 32)
; CHECK-NEXT: ret i33 [[R]]
;
%r = call i33 @llvm.fshr.i33(i33 %x, i33 %y, i33 34)
@ -376,7 +376,7 @@ define i33 @fshr_constant_shift_amount_modulo_bitwidth_constexpr(i33 %x, i33 %y)
define <2 x i32> @fshr_constant_shift_amount_modulo_bitwidth_vec(<2 x i32> %x, <2 x i32> %y) {
; CHECK-LABEL: @fshr_constant_shift_amount_modulo_bitwidth_vec(
; CHECK-NEXT: [[R:%.*]] = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 2, i32 31>)
; CHECK-NEXT: [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 30, i32 1>)
; CHECK-NEXT: ret <2 x i32> [[R]]
;
%r = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> %x, <2 x i32> %y, <2 x i32> <i32 34, i32 -1>)
@ -466,7 +466,7 @@ define i32 @fshl_both_ops_demanded(i32 %x, i32 %y) {
define i33 @fshr_both_ops_demanded(i33 %x, i33 %y) {
; CHECK-LABEL: @fshr_both_ops_demanded(
; CHECK-NEXT: [[Z:%.*]] = call i33 @llvm.fshr.i33(i33 [[X:%.*]], i33 [[Y:%.*]], i33 26)
; CHECK-NEXT: [[Z:%.*]] = call i33 @llvm.fshl.i33(i33 [[X:%.*]], i33 [[Y:%.*]], i33 7)
; CHECK-NEXT: [[R:%.*]] = and i33 [[Z]], 192
; CHECK-NEXT: ret i33 [[R]]
;