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veera-sivarajanveera-sivarajan
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Fold X udiv Y to X lshr cttz(Y) if Y is a power of 2
1 parent 72b6b01 commit 7b4831d

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+37
-12
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3 files changed

+37
-12
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‎llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

+17-2
Original file line numberDiff line numberDiff line change
@@ -1598,8 +1598,23 @@ Instruction *InstCombinerImpl::visitUDiv(BinaryOperator &I) {
15981598
return Lshr;
15991599
}
16001600

1601-
// Op1 udiv Op2 -> Op1 lshr log2(Op2), if log2() folds away.
1602-
if (Value *Res = tryGetLog2(Op1, /*AssumeNonZero=*/true))
1601+
auto GetShiftableDenom = [&](Value *Denom) -> Value * {
1602+
// Op0 udiv Op1 -> Op0 lshr log2(Op1), if log2() folds away.
1603+
if (Value *Log2 = tryGetLog2(Op1, /*AssumeNonZero=*/true))
1604+
return Log2;
1605+
1606+
// Op0 udiv Op1 -> Op0 lshr cttz(Op1), if Op1 is a power of 2.
1607+
if (isKnownToBeAPowerOfTwo(Denom, /*OrZero=*/true, /*Depth=*/0, &I))
1608+
// This will increase instruction count but it's okay
1609+
// since bitwise operations are substantially faster than
1610+
// division.
1611+
return Builder.CreateBinaryIntrinsic(Intrinsic::cttz, Denom,
1612+
Builder.getTrue());
1613+
1614+
return nullptr;
1615+
};
1616+
1617+
if (auto *Res = GetShiftableDenom(Op1))
16031618
return replaceInstUsesWith(
16041619
I, Builder.CreateLShr(Op0, Res, I.getName(), I.isExact()));
16051620

‎llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll

+4-2
Original file line numberDiff line numberDiff line change
@@ -218,7 +218,8 @@ define i32 @vscale_slt_with_vp_umin(ptr nocapture %A, i32 %n) mustprogress vscal
218218
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
219219
; CHECK: for.end:
220220
; CHECK-NEXT: [[TMP0:%.*]] = add nsw i32 [[N]], -1
221-
; CHECK-NEXT: [[TMP1:%.*]] = udiv i32 [[TMP0]], [[VF]]
221+
; CHECK-NEXT: [[TMP5:%.*]] = call range(i32 2, 33) i32 @llvm.cttz.i32(i32 [[VF]], i1 true)
222+
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[TMP0]], [[TMP5]]
222223
; CHECK-NEXT: [[TMP2:%.*]] = mul i32 [[TMP1]], [[VSCALE]]
223224
; CHECK-NEXT: [[TMP3:%.*]] = shl i32 [[TMP2]], 2
224225
; CHECK-NEXT: [[TMP4:%.*]] = sub i32 [[N]], [[TMP3]]
@@ -270,7 +271,8 @@ define i32 @vscale_slt_with_vp_umin2(ptr nocapture %A, i32 %n) mustprogress vsca
270271
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
271272
; CHECK: for.end:
272273
; CHECK-NEXT: [[TMP0:%.*]] = add i32 [[N]], -1
273-
; CHECK-NEXT: [[TMP1:%.*]] = udiv i32 [[TMP0]], [[VF]]
274+
; CHECK-NEXT: [[TMP5:%.*]] = call range(i32 2, 33) i32 @llvm.cttz.i32(i32 [[VF]], i1 true)
275+
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[TMP0]], [[TMP5]]
274276
; CHECK-NEXT: [[TMP2:%.*]] = mul i32 [[TMP1]], [[VSCALE]]
275277
; CHECK-NEXT: [[TMP3:%.*]] = shl i32 [[TMP2]], 2
276278
; CHECK-NEXT: [[TMP4:%.*]] = sub i32 [[N]], [[TMP3]]

‎llvm/test/Transforms/InstCombine/div-shift.ll

+16-8
Original file line numberDiff line numberDiff line change
@@ -148,7 +148,8 @@ define i8 @udiv_umin_extra_use(i8 %x, i8 %y, i8 %z) {
148148
; CHECK-NEXT: [[Z2:%.*]] = shl nuw i8 1, [[Z:%.*]]
149149
; CHECK-NEXT: [[M:%.*]] = call i8 @llvm.umin.i8(i8 [[Y2]], i8 [[Z2]])
150150
; CHECK-NEXT: call void @use(i8 [[M]])
151-
; CHECK-NEXT: [[D:%.*]] = udiv i8 [[X:%.*]], [[M]]
151+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[M]], i1 true)
152+
; CHECK-NEXT: [[D:%.*]] = lshr i8 [[X:%.*]], [[TMP1]]
152153
; CHECK-NEXT: ret i8 [[D]]
153154
;
154155
%y2 = shl i8 1, %y
@@ -165,7 +166,8 @@ define i8 @udiv_smin(i8 %x, i8 %y, i8 %z) {
165166
; CHECK-NEXT: [[Y2:%.*]] = shl nuw i8 1, [[Y:%.*]]
166167
; CHECK-NEXT: [[Z2:%.*]] = shl nuw i8 1, [[Z:%.*]]
167168
; CHECK-NEXT: [[M:%.*]] = call i8 @llvm.smin.i8(i8 [[Y2]], i8 [[Z2]])
168-
; CHECK-NEXT: [[D:%.*]] = udiv i8 [[X:%.*]], [[M]]
169+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[M]], i1 true)
170+
; CHECK-NEXT: [[D:%.*]] = lshr i8 [[X:%.*]], [[TMP1]]
169171
; CHECK-NEXT: ret i8 [[D]]
170172
;
171173
%y2 = shl i8 1, %y
@@ -181,7 +183,8 @@ define i8 @udiv_smax(i8 %x, i8 %y, i8 %z) {
181183
; CHECK-NEXT: [[Y2:%.*]] = shl nuw i8 1, [[Y:%.*]]
182184
; CHECK-NEXT: [[Z2:%.*]] = shl nuw i8 1, [[Z:%.*]]
183185
; CHECK-NEXT: [[M:%.*]] = call i8 @llvm.smax.i8(i8 [[Y2]], i8 [[Z2]])
184-
; CHECK-NEXT: [[D:%.*]] = udiv i8 [[X:%.*]], [[M]]
186+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[M]], i1 true)
187+
; CHECK-NEXT: [[D:%.*]] = lshr i8 [[X:%.*]], [[TMP1]]
185188
; CHECK-NEXT: ret i8 [[D]]
186189
;
187190
%y2 = shl i8 1, %y
@@ -1006,7 +1009,8 @@ define i8 @udiv_fail_shl_overflow(i8 %x, i8 %y) {
10061009
; CHECK-LABEL: @udiv_fail_shl_overflow(
10071010
; CHECK-NEXT: [[SHL:%.*]] = shl i8 2, [[Y:%.*]]
10081011
; CHECK-NEXT: [[MIN:%.*]] = call i8 @llvm.umax.i8(i8 [[SHL]], i8 1)
1009-
; CHECK-NEXT: [[MUL:%.*]] = udiv i8 [[X:%.*]], [[MIN]]
1012+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[MIN]], i1 true)
1013+
; CHECK-NEXT: [[MUL:%.*]] = lshr i8 [[X:%.*]], [[TMP1]]
10101014
; CHECK-NEXT: ret i8 [[MUL]]
10111015
;
10121016
%shl = shl i8 2, %y
@@ -1302,7 +1306,8 @@ define i8 @udiv_if_power_of_two(i8 %x, i8 %y) {
13021306
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
13031307
; CHECK-NEXT: br i1 [[TMP1]], label [[BB1:%.*]], label [[BB3:%.*]]
13041308
; CHECK: bb1:
1305-
; CHECK-NEXT: [[TMP3:%.*]] = udiv i8 [[X:%.*]], [[Y]]
1309+
; CHECK-NEXT: [[TMP2:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[Y]], i1 true)
1310+
; CHECK-NEXT: [[TMP3:%.*]] = lshr i8 [[X:%.*]], [[TMP2]]
13061311
; CHECK-NEXT: br label [[BB3]]
13071312
; CHECK: bb3:
13081313
; CHECK-NEXT: [[_0_SROA_0_0:%.*]] = phi i8 [ [[TMP3]], [[BB1]] ], [ 0, [[START:%.*]] ]
@@ -1328,7 +1333,8 @@ define i8 @udiv_exact_assume_power_of_two(i8 %x, i8 %y) {
13281333
; CHECK-NEXT: [[TMP0:%.*]] = tail call range(i8 1, 9) i8 @llvm.ctpop.i8(i8 [[Y:%.*]])
13291334
; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[TMP0]], 1
13301335
; CHECK-NEXT: tail call void @llvm.assume(i1 [[COND]])
1331-
; CHECK-NEXT: [[_0:%.*]] = udiv exact i8 [[X:%.*]], [[Y]]
1336+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[Y]], i1 true)
1337+
; CHECK-NEXT: [[_0:%.*]] = lshr exact i8 [[X:%.*]], [[TMP1]]
13321338
; CHECK-NEXT: ret i8 [[_0]]
13331339
;
13341340
start:
@@ -1345,7 +1351,8 @@ define i7 @udiv_assume_power_of_two_illegal_type(i7 %x, i7 %y) {
13451351
; CHECK-NEXT: [[TMP0:%.*]] = tail call range(i7 1, 8) i7 @llvm.ctpop.i7(i7 [[Y:%.*]])
13461352
; CHECK-NEXT: [[COND:%.*]] = icmp eq i7 [[TMP0]], 1
13471353
; CHECK-NEXT: tail call void @llvm.assume(i1 [[COND]])
1348-
; CHECK-NEXT: [[_0:%.*]] = udiv i7 [[X:%.*]], [[Y]]
1354+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i7 0, 8) i7 @llvm.cttz.i7(i7 [[Y]], i1 true)
1355+
; CHECK-NEXT: [[_0:%.*]] = lshr i7 [[X:%.*]], [[TMP1]]
13491356
; CHECK-NEXT: ret i7 [[_0]]
13501357
;
13511358
start:
@@ -1362,7 +1369,8 @@ define i8 @udiv_assume_power_of_two_multiuse(i8 %x, i8 %y) {
13621369
; CHECK-NEXT: [[TMP0:%.*]] = tail call range(i8 1, 9) i8 @llvm.ctpop.i8(i8 [[Y:%.*]])
13631370
; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[TMP0]], 1
13641371
; CHECK-NEXT: tail call void @llvm.assume(i1 [[COND]])
1365-
; CHECK-NEXT: [[_0:%.*]] = udiv i8 [[X:%.*]], [[Y]]
1372+
; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[Y]], i1 true)
1373+
; CHECK-NEXT: [[_0:%.*]] = lshr i8 [[X:%.*]], [[TMP1]]
13661374
; CHECK-NEXT: call void @use(i8 [[_0]])
13671375
; CHECK-NEXT: ret i8 [[_0]]
13681376
;

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