[llvm] [InstCombine] Fold (X / C) < X and (X >> C) < X into X > 0 (PR #85555)
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Sun Mar 17 12:21:06 PDT 2024
https://github.com/Poseydon42 updated https://github.com/llvm/llvm-project/pull/85555
>From 6bfc90a80e5f933c8acafadb7352292df8f15dee Mon Sep 17 00:00:00 2001
From: Poseydon42 <vvmposeydon at gmail.com>
Date: Sat, 16 Mar 2024 21:09:41 +0000
Subject: [PATCH 1/2] [IstCombine] Add tests for (X / C) < X and (X >> C) < X
folds
---
.../InstCombine/icmp-div-constant.ll | 79 +++++++++++++++++++
1 file changed, 79 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/icmp-div-constant.ll b/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
index 8dcb96284685ff..5b95144fe633c1 100644
--- a/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
@@ -375,3 +375,82 @@ define i1 @sdiv_eq_smin_use(i32 %x, i32 %y) {
%r = icmp eq i32 %d, -2147483648
ret i1 %r
}
+
+; Folding (X / C) < X => X > 0 for C != 1
+
+define i1 @sdiv_x_by_const_cmp_x(i32 %x) {
+; CHECK-LABEL: @sdiv_x_by_const_cmp_x(
+; CHECK-NEXT: [[TMP2:%.*]] = sdiv i32 [[X:%.*]], 123
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[TMP2]], [[X]]
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ %1 = sdiv i32 %x, 123
+ %2 = icmp slt i32 %1, %x
+ ret i1 %2
+}
+
+define i1 @udiv_x_by_const_cmp_x(i32 %x) {
+; CHECK-LABEL: @udiv_x_by_const_cmp_x(
+; CHECK-NEXT: [[TMP2:%.*]] = udiv i32 [[X:%.*]], 123
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[TMP2]], [[X]]
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ %1 = udiv i32 %x, 123
+ %2 = icmp slt i32 %1, %x
+ ret i1 %2
+}
+
+; Same as above but with right shift instead of division (C != 0)
+
+define i1 @lshr_x_by_const_cmp_x(i32 %x) {
+; CHECK-LABEL: @lshr_x_by_const_cmp_x(
+; CHECK-NEXT: [[TMP2:%.*]] = lshr i32 [[X:%.*]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[TMP2]], [[X]]
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ %1 = lshr i32 %x, 1
+ %2 = icmp slt i32 %1, %x
+ ret i1 %2
+}
+
+; Negative tests for the folds above
+
+define i1 @sdiv_x_by_1_cmp_x_negative(i32 %x) {
+; CHECK-LABEL: @sdiv_x_by_1_cmp_x_negative(
+; CHECK-NEXT: ret i1 false
+;
+ %1 = sdiv i32 %x, 1
+ %2 = icmp slt i32 %1, %x
+ ret i1 %2
+}
+
+define i1 @sdiv_x_by_1_cmp_y(i32 %x, i32 %y) {
+; CHECK-LABEL: @sdiv_x_by_1_cmp_y(
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv i32 [[X:%.*]], 123
+; CHECK-NEXT: [[TMP2:%.*]] = icmp slt i32 [[TMP1]], [[Y:%.*]]
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ %1 = sdiv i32 %x, 123
+ %2 = icmp slt i32 %1, %y
+ ret i1 %2
+}
+
+define i1 @lshr_x_by_0_cmp_x(i32 %x) {
+; CHECK-LABEL: @lshr_x_by_0_cmp_x(
+; CHECK-NEXT: ret i1 false
+;
+ %1 = lshr i32 %x, 0
+ %2 = icmp slt i32 %1, %x
+ ret i1 %2
+}
+
+define i1 @lshr_x_by_const_cmp_y(i32 %x, i32 %y) {
+; CHECK-LABEL: @lshr_x_by_const_cmp_y(
+; CHECK-NEXT: [[X:%.*]] = lshr i32 [[X1:%.*]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[X]], [[Y:%.*]]
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ %1 = lshr i32 %x, 1
+ %2 = icmp slt i32 %1, %y
+ ret i1 %2
+}
>From ba272c141236f63ed26c227d36cd5a0387fa1a2c Mon Sep 17 00:00:00 2001
From: Poseydon42 <vvmposeydon at gmail.com>
Date: Sat, 16 Mar 2024 22:13:15 +0000
Subject: [PATCH 2/2] [InstCombine] Fold (X / C) < X and (X >> C) < X into X >
0
---
.../InstCombine/InstCombineCompares.cpp | 25 +++++++++++++++++++
.../InstCombine/icmp-div-constant.ll | 9 +++----
2 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 0dce0077bf1588..415ea61362776d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -7406,6 +7406,31 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
if (Instruction *Res = foldReductionIdiom(I, Builder, DL))
return Res;
+ // Folding (X / Y) < X => X > 0 for some constant Y other than 0 or 1
+ {
+ Constant *Divisor;
+ Value *Dividend;
+ if (match(Op0,
+ m_CombineOr(m_SDiv(m_Value(Dividend), m_ImmConstant(Divisor)),
+ m_UDiv(m_Value(Dividend), m_ImmConstant(Divisor)))) &&
+ match(Op1, m_Deferred(Dividend)) &&
+ !(Divisor->isZeroValue() || Divisor->isOneValue())) {
+ return new ICmpInst(ICmpInst::ICMP_SGT, Dividend,
+ Constant::getNullValue(Dividend->getType()));
+ }
+ }
+
+ // Another case of this fold is (X >> Y) < X => X > 0 if Y != 0
+ {
+ Constant *Shift;
+ Value *V;
+ if (match(Op0, m_LShr(m_Value(V), m_ImmConstant(Shift))) &&
+ match(Op1, m_Deferred(V)) && !Shift->isZeroValue()) {
+ return new ICmpInst(ICmpInst::ICMP_SGT, V,
+ Constant::getNullValue(V->getType()));
+ }
+ }
+
return Changed ? &I : nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/icmp-div-constant.ll b/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
index 5b95144fe633c1..0bdfa5daa547a5 100644
--- a/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
@@ -380,8 +380,7 @@ define i1 @sdiv_eq_smin_use(i32 %x, i32 %y) {
define i1 @sdiv_x_by_const_cmp_x(i32 %x) {
; CHECK-LABEL: @sdiv_x_by_const_cmp_x(
-; CHECK-NEXT: [[TMP2:%.*]] = sdiv i32 [[X:%.*]], 123
-; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[TMP2]], [[X]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[X:%.*]], 0
; CHECK-NEXT: ret i1 [[TMP1]]
;
%1 = sdiv i32 %x, 123
@@ -391,8 +390,7 @@ define i1 @sdiv_x_by_const_cmp_x(i32 %x) {
define i1 @udiv_x_by_const_cmp_x(i32 %x) {
; CHECK-LABEL: @udiv_x_by_const_cmp_x(
-; CHECK-NEXT: [[TMP2:%.*]] = udiv i32 [[X:%.*]], 123
-; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[TMP2]], [[X]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[X:%.*]], 0
; CHECK-NEXT: ret i1 [[TMP1]]
;
%1 = udiv i32 %x, 123
@@ -404,8 +402,7 @@ define i1 @udiv_x_by_const_cmp_x(i32 %x) {
define i1 @lshr_x_by_const_cmp_x(i32 %x) {
; CHECK-LABEL: @lshr_x_by_const_cmp_x(
-; CHECK-NEXT: [[TMP2:%.*]] = lshr i32 [[X:%.*]], 1
-; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[TMP2]], [[X]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[X:%.*]], 0
; CHECK-NEXT: ret i1 [[TMP1]]
;
%1 = lshr i32 %x, 1
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