[llvm] [InstCombine] lshr (mul (X, 2^N + 1)), N -> add (X, lshr(X, N)) (PR #90295)
via llvm-commits
llvm-commits at lists.llvm.org
Tue May 14 06:21:29 PDT 2024
https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/90295
>From 86c0ef2a24a81ee07641c4adb7a1452bdf722ca8 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Wed, 1 May 2024 22:50:44 -0400
Subject: [PATCH 1/3] [InstCombine] Pre-commit tests (NFC)
---
llvm/test/Transforms/InstCombine/ashr-lshr.ll | 63 +++++++++++++++++++
1 file changed, 63 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/ashr-lshr.ll b/llvm/test/Transforms/InstCombine/ashr-lshr.ll
index ac206dc7999dd..d5de402e52ee7 100644
--- a/llvm/test/Transforms/InstCombine/ashr-lshr.ll
+++ b/llvm/test/Transforms/InstCombine/ashr-lshr.ll
@@ -604,3 +604,66 @@ define <2 x i8> @ashr_known_pos_exact_vec(<2 x i8> %x, <2 x i8> %y) {
%r = ashr exact <2 x i8> %p, %y
ret <2 x i8> %r
}
+
+define i32 @lshr_mul_times_3_div_2(i32 %0) {
+; CHECK-LABEL: @lshr_mul_times_3_div_2(
+; CHECK-NEXT: [[MUL:%.*]] = mul nuw nsw i32 [[TMP0:%.*]], 3
+; CHECK-NEXT: [[LSHR:%.*]] = lshr i32 [[MUL]], 1
+; CHECK-NEXT: ret i32 [[LSHR]]
+;
+ %mul = mul nsw nuw i32 %0, 3
+ %lshr = lshr i32 %mul, 1
+ ret i32 %lshr
+}
+
+define i32 @lshr_mul_times_3_div_2_exact(i32 %x) {
+; CHECK-LABEL: @lshr_mul_times_3_div_2_exact(
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i32 [[X:%.*]], 3
+; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[MUL]], 1
+; CHECK-NEXT: ret i32 [[LSHR]]
+;
+ %mul = mul nsw i32 %x, 3
+ %lshr = lshr exact i32 %mul, 1
+ ret i32 %lshr
+}
+
+; Negative test
+
+define i32 @lshr_mul_times_3_div_2_no_flags(i32 %0) {
+; CHECK-LABEL: @lshr_mul_times_3_div_2_no_flags(
+; CHECK-NEXT: [[MUL:%.*]] = mul i32 [[TMP0:%.*]], 3
+; CHECK-NEXT: [[LSHR:%.*]] = lshr i32 [[MUL]], 1
+; CHECK-NEXT: ret i32 [[LSHR]]
+;
+ %mul = mul i32 %0, 3
+ %lshr = lshr i32 %mul, 1
+ ret i32 %lshr
+}
+
+; Negative test
+
+define i32 @mul_times_3_div_2_multiuse_lshr(i32 %x) {
+; CHECK-LABEL: @mul_times_3_div_2_multiuse_lshr(
+; CHECK-NEXT: [[MUL:%.*]] = mul nuw i32 [[X:%.*]], 3
+; CHECK-NEXT: [[RES:%.*]] = lshr i32 [[MUL]], 1
+; CHECK-NEXT: call void @use(i32 [[MUL]])
+; CHECK-NEXT: ret i32 [[RES]]
+;
+ %mul = mul nuw i32 %x, 3
+ %res = lshr i32 %mul, 1
+ call void @use (i32 %mul)
+ ret i32 %res
+}
+
+define i32 @lshr_mul_times_3_div_2_exact_2(i32 %x) {
+; CHECK-LABEL: @lshr_mul_times_3_div_2_exact_2(
+; CHECK-NEXT: [[MUL:%.*]] = mul nuw i32 [[X:%.*]], 3
+; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[MUL]], 1
+; CHECK-NEXT: ret i32 [[LSHR]]
+;
+ %mul = mul nuw i32 %x, 3
+ %lshr = lshr exact i32 %mul, 1
+ ret i32 %lshr
+}
+
+declare void @use(i32)
>From eb86d7132ad8ca4375e445edf92779b3e72e7df0 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Mon, 6 May 2024 17:07:29 -0400
Subject: [PATCH 2/3] [InstCombine] lshr (mul (X, 2^N + 1)), N -> add (X,
lshr(X, N))
A generalization of the proposed x * 3/2 -> x + (x >> 1) transformation but applies to all multiplications that are one more than a power of 2.
Proof: https://alive2.llvm.org/ce/z/WaZYvn
---
.../InstCombine/InstCombineShifts.cpp | 35 +++++++++++++++----
llvm/test/Transforms/InstCombine/ashr-lshr.ll | 12 +++----
llvm/test/Transforms/InstCombine/lshr.ll | 4 +--
3 files changed, 36 insertions(+), 15 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 8847de3667130..f6e26b5ff42cc 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -1457,13 +1457,24 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
const APInt *MulC;
if (match(Op0, m_NUWMul(m_Value(X), m_APInt(MulC)))) {
- // Look for a "splat" mul pattern - it replicates bits across each half of
- // a value, so a right shift is just a mask of the low bits:
- // lshr i[2N] (mul nuw X, (2^N)+1), N --> and iN X, (2^N)-1
- // TODO: Generalize to allow more than just half-width shifts?
- if (BitWidth > 2 && ShAmtC * 2 == BitWidth && (*MulC - 1).isPowerOf2() &&
- MulC->logBase2() == ShAmtC)
- return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, *MulC - 2));
+ if (BitWidth > 2 && (*MulC - 1).isPowerOf2() &&
+ MulC->logBase2() == ShAmtC) {
+ // Look for a "splat" mul pattern - it replicates bits across each half
+ // of a value, so a right shift is just a mask of the low bits:
+ // lshr i[2N] (mul nuw X, (2^N)+1), N --> and iN X, (2^N)-1
+ if (ShAmtC * 2 == BitWidth)
+ return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, *MulC - 2));
+
+ // lshr (mul nuw (X, 2^N + 1)), N -> add nuw (X, lshr(X, N))
+ if (Op0->hasOneUse()) {
+ auto *NewAdd = BinaryOperator::CreateNUWAdd(
+ X, Builder.CreateLShr(X, ConstantInt::get(Ty, ShAmtC), "",
+ I.isExact()));
+ NewAdd->setHasNoSignedWrap(
+ cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap());
+ return NewAdd;
+ }
+ }
// The one-use check is not strictly necessary, but codegen may not be
// able to invert the transform and perf may suffer with an extra mul
@@ -1483,6 +1494,16 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
}
}
+ // lshr (mul nsw (X, 2^N + 1)), N -> add nsw (X, lshr(X, N))
+ if (match(Op0, m_OneUse(m_NSWMul(m_Value(X), m_APInt(MulC))))) {
+ if (BitWidth > 2 && (*MulC - 1).isPowerOf2() &&
+ MulC->logBase2() == ShAmtC) {
+ return BinaryOperator::CreateNSWAdd(
+ X, Builder.CreateLShr(X, ConstantInt::get(Ty, ShAmtC), "",
+ I.isExact()));
+ }
+ }
+
// Try to narrow bswap.
// In the case where the shift amount equals the bitwidth difference, the
// shift is eliminated.
diff --git a/llvm/test/Transforms/InstCombine/ashr-lshr.ll b/llvm/test/Transforms/InstCombine/ashr-lshr.ll
index d5de402e52ee7..43fd07a214323 100644
--- a/llvm/test/Transforms/InstCombine/ashr-lshr.ll
+++ b/llvm/test/Transforms/InstCombine/ashr-lshr.ll
@@ -607,8 +607,8 @@ define <2 x i8> @ashr_known_pos_exact_vec(<2 x i8> %x, <2 x i8> %y) {
define i32 @lshr_mul_times_3_div_2(i32 %0) {
; CHECK-LABEL: @lshr_mul_times_3_div_2(
-; CHECK-NEXT: [[MUL:%.*]] = mul nuw nsw i32 [[TMP0:%.*]], 3
-; CHECK-NEXT: [[LSHR:%.*]] = lshr i32 [[MUL]], 1
+; CHECK-NEXT: [[TMP2:%.*]] = lshr i32 [[TMP0:%.*]], 1
+; CHECK-NEXT: [[LSHR:%.*]] = add nuw nsw i32 [[TMP2]], [[TMP0]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%mul = mul nsw nuw i32 %0, 3
@@ -618,8 +618,8 @@ define i32 @lshr_mul_times_3_div_2(i32 %0) {
define i32 @lshr_mul_times_3_div_2_exact(i32 %x) {
; CHECK-LABEL: @lshr_mul_times_3_div_2_exact(
-; CHECK-NEXT: [[MUL:%.*]] = mul nsw i32 [[X:%.*]], 3
-; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[MUL]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = lshr exact i32 [[X:%.*]], 1
+; CHECK-NEXT: [[LSHR:%.*]] = add nsw i32 [[TMP1]], [[X]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%mul = mul nsw i32 %x, 3
@@ -657,8 +657,8 @@ define i32 @mul_times_3_div_2_multiuse_lshr(i32 %x) {
define i32 @lshr_mul_times_3_div_2_exact_2(i32 %x) {
; CHECK-LABEL: @lshr_mul_times_3_div_2_exact_2(
-; CHECK-NEXT: [[MUL:%.*]] = mul nuw i32 [[X:%.*]], 3
-; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[MUL]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = lshr exact i32 [[X:%.*]], 1
+; CHECK-NEXT: [[LSHR:%.*]] = add nuw i32 [[TMP1]], [[X]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%mul = mul nuw i32 %x, 3
diff --git a/llvm/test/Transforms/InstCombine/lshr.ll b/llvm/test/Transforms/InstCombine/lshr.ll
index 563e669f90353..ea42e591c1603 100644
--- a/llvm/test/Transforms/InstCombine/lshr.ll
+++ b/llvm/test/Transforms/InstCombine/lshr.ll
@@ -630,8 +630,8 @@ define i32 @mul_splat_fold_wrong_lshr_const(i32 %x) {
define i32 @mul_splat_fold_no_nuw(i32 %x) {
; CHECK-LABEL: @mul_splat_fold_no_nuw(
-; CHECK-NEXT: [[M:%.*]] = mul nsw i32 [[X:%.*]], 65537
-; CHECK-NEXT: [[T:%.*]] = lshr i32 [[M]], 16
+; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 16
+; CHECK-NEXT: [[T:%.*]] = add nsw i32 [[TMP1]], [[X]]
; CHECK-NEXT: ret i32 [[T]]
;
%m = mul nsw i32 %x, 65537
>From 87ca9fe51f98fbafd52122690e3189baba5ec8cb Mon Sep 17 00:00:00 2001
From: AtariDreams <gfunni234 at gmail.com>
Date: Tue, 14 May 2024 09:21:19 -0400
Subject: [PATCH 3/3] Update lshr.ll
---
llvm/test/Transforms/InstCombine/lshr.ll | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/test/Transforms/InstCombine/lshr.ll b/llvm/test/Transforms/InstCombine/lshr.ll
index ea42e591c1603..c39bceaf74f2b 100644
--- a/llvm/test/Transforms/InstCombine/lshr.ll
+++ b/llvm/test/Transforms/InstCombine/lshr.ll
@@ -626,7 +626,7 @@ define i32 @mul_splat_fold_wrong_lshr_const(i32 %x) {
ret i32 %t
}
-; Negative test
+; Negative test (but simplifies into a different transform)
define i32 @mul_splat_fold_no_nuw(i32 %x) {
; CHECK-LABEL: @mul_splat_fold_no_nuw(
More information about the llvm-commits
mailing list