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[InstCombine] fold udiv with common factor

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((X *nuw Y) >> Z) / X --> Y >> Z

https://alive2.llvm.org/ce/z/x3kKnq

This is similar to 6b869be810 / 8da2fa856f, but I have
not found a signed equivalent, so it's just an unsigned
match for now.
This commit is contained in:
Sanjay Patel
2022-10-10 07:21:23 -04:00
parent 6876004f33
commit 9cff4711ac
2 changed files with 31 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@@ -1157,6 +1157,16 @@ Instruction *InstCombinerImpl::visitUDiv(BinaryOperator &I) {
return BinaryOperator::CreateUDiv(A, X);
}
// Look through a right-shift to find the common factor:
// ((Op1 *nuw A) >> B) / Op1 --> A >> B
if (match(Op0, m_LShr(m_NUWMul(m_Specific(Op1), m_Value(A)), m_Value(B))) ||
match(Op0, m_LShr(m_NUWMul(m_Value(A), m_Specific(Op1)), m_Value(B)))) {
Instruction *Lshr = BinaryOperator::CreateLShr(A, B);
if (I.isExact() && cast<PossiblyExactOperator>(Op0)->isExact())
Lshr->setIsExact();
return Lshr;
}
// Op1 udiv Op2 -> Op1 lshr log2(Op2), if log2() folds away.
if (takeLog2(Builder, Op1, /*Depth*/0, /*DoFold*/false)) {
Value *Res = takeLog2(Builder, Op1, /*Depth*/0, /*DoFold*/true);

31
llvm/test/Transforms/InstCombine/div-shift.ll
View File

@@ -619,11 +619,11 @@ define i8 @udiv_shl_nuw_use(i8 %x, i8 %y, i8 %z) {
ret i8 %d
}
; ((X * Y) >> Z) / X --> Y >> Z
define i8 @udiv_lshr_mul_nuw(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @udiv_lshr_mul_nuw(
; CHECK-NEXT: [[M:%.*]] = mul nuw i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[S:%.*]] = lshr i8 [[M]], [[Z:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[S]], [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[Y:%.*]], [[Z:%.*]]
; CHECK-NEXT: ret i8 [[DIV]]
;
%m = mul nuw i8 %x, %y
@@ -632,11 +632,11 @@ define i8 @udiv_lshr_mul_nuw(i8 %x, i8 %y, i8 %z) {
ret i8 %div
}
; ((Y * X) >> Z) / X --> Y >> Z
define <2 x i4> @udiv_lshr_mul_nuw_exact_commute1(<2 x i4> %x, <2 x i4> %y, <2 x i4> %z) {
; CHECK-LABEL: @udiv_lshr_mul_nuw_exact_commute1(
; CHECK-NEXT: [[M:%.*]] = mul nuw <2 x i4> [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[S:%.*]] = lshr exact <2 x i4> [[M]], [[Z:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = udiv exact <2 x i4> [[S]], [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr exact <2 x i4> [[Y:%.*]], [[Z:%.*]]
; CHECK-NEXT: ret <2 x i4> [[DIV]]
;
%m = mul nuw <2 x i4> %y, %x
@@ -645,6 +645,8 @@ define <2 x i4> @udiv_lshr_mul_nuw_exact_commute1(<2 x i4> %x, <2 x i4> %y, <2 x
ret <2 x i4> %div
}
; negative test - mul is shifted amount, not shifted value
define i8 @udiv_lshr_mul_nuw_commute2(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @udiv_lshr_mul_nuw_commute2(
; CHECK-NEXT: [[M:%.*]] = mul nuw i8 [[Y:%.*]], [[X:%.*]]
@@ -658,12 +660,13 @@ define i8 @udiv_lshr_mul_nuw_commute2(i8 %x, i8 %y, i8 %z) {
ret i8 %div
}
; extra uses are ok
define i8 @udiv_lshr_mul_nuw_use1(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @udiv_lshr_mul_nuw_use1(
; CHECK-NEXT: [[M:%.*]] = mul nuw i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: call void @use(i8 [[M]])
; CHECK-NEXT: [[S:%.*]] = lshr i8 [[M]], [[Z:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[S]], [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[Y]], [[Z:%.*]]
; CHECK-NEXT: ret i8 [[DIV]]
;
%m = mul nuw i8 %x, %y
@@ -673,12 +676,14 @@ define i8 @udiv_lshr_mul_nuw_use1(i8 %x, i8 %y, i8 %z) {
ret i8 %div
}
; extra uses are ok
define i8 @udiv_lshr_mul_nuw_use2(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @udiv_lshr_mul_nuw_use2(
; CHECK-NEXT: [[M:%.*]] = mul nuw i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[S:%.*]] = lshr i8 [[M]], [[Z:%.*]]
; CHECK-NEXT: call void @use(i8 [[S]])
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[S]], [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[Y]], [[Z]]
; CHECK-NEXT: ret i8 [[DIV]]
;
%m = mul nuw i8 %x, %y
@@ -688,13 +693,15 @@ define i8 @udiv_lshr_mul_nuw_use2(i8 %x, i8 %y, i8 %z) {
ret i8 %div
}
; extra uses are ok
define i8 @udiv_lshr_mul_nuw_use3(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @udiv_lshr_mul_nuw_use3(
; CHECK-NEXT: [[M:%.*]] = mul nuw i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: call void @use(i8 [[M]])
; CHECK-NEXT: [[S:%.*]] = lshr i8 [[M]], [[Z:%.*]]
; CHECK-NEXT: call void @use(i8 [[S]])
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[S]], [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[Y]], [[Z]]
; CHECK-NEXT: ret i8 [[DIV]]
;
%m = mul nuw i8 %x, %y
@@ -705,6 +712,8 @@ define i8 @udiv_lshr_mul_nuw_use3(i8 %x, i8 %y, i8 %z) {
ret i8 %div
}
; negative test - must have nuw
define i8 @udiv_lshr_mul_nsw(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @udiv_lshr_mul_nsw(
; CHECK-NEXT: [[M:%.*]] = mul nsw i8 [[X:%.*]], [[Y:%.*]]
@@ -718,6 +727,8 @@ define i8 @udiv_lshr_mul_nsw(i8 %x, i8 %y, i8 %z) {
ret i8 %div
}
; negative test - doesn't fold with signed div
define i8 @sdiv_lshr_mul_nsw(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @sdiv_lshr_mul_nsw(
; CHECK-NEXT: [[M:%.*]] = mul nsw i8 [[X:%.*]], [[Y:%.*]]