[llvm] [InstCombine] Simplify nested selects with implied condition (PR #83739)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Sun Mar 3 11:31:10 PST 2024
https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/83739
This patch does the following simplification:
```
sel1 = select cond1, X, Y
sel2 = select cond2, sel1, Z
-->
sel2 = select cond2, X, Z if cond2 implies cond1
sel2 = select cond2, Y, Z if cond2 implies !cond1
```
Alive2: https://alive2.llvm.org/ce/z/9A_arU
It cannot be done in CVP/SCCP since we should guarantee that `cond2` is not an undef.
>From 2abbc125b2d8d9fedf9961eeef853792dd7aadd1 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 4 Mar 2024 03:05:51 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.
---
.../Transforms/InstCombine/nested-select.ll | 92 +++++++++++++++++++
1 file changed, 92 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/nested-select.ll b/llvm/test/Transforms/InstCombine/nested-select.ll
index 42a0f81e7b85a2..a7cdee1483b46a 100644
--- a/llvm/test/Transforms/InstCombine/nested-select.ll
+++ b/llvm/test/Transforms/InstCombine/nested-select.ll
@@ -498,3 +498,95 @@ define i1 @orcond.111.inv.all.conds(i1 %inner.cond, i1 %alt.cond, i1 %inner.sel.
%outer.sel = select i1 %not.outer.cond, i1 true, i1 %inner.sel
ret i1 %outer.sel
}
+
+define i8 @test_implied_true(i8 %x) {
+; CHECK-LABEL: @test_implied_true(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X:%.*]], 10
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 [[SEL1]], i8 20
+; CHECK-NEXT: ret i8 [[SEL2]]
+;
+ %cmp1 = icmp slt i8 %x, 10
+ %cmp2 = icmp slt i8 %x, 0
+ %sel1 = select i1 %cmp1, i8 0, i8 5
+ %sel2 = select i1 %cmp2, i8 %sel1, i8 20
+ ret i8 %sel2
+}
+
+define <2 x i8> @test_implied_true_vec(<2 x i8> %x) {
+; CHECK-LABEL: @test_implied_true_vec(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 10, i8 10>
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt <2 x i8> [[X]], zeroinitializer
+; CHECK-NEXT: [[SEL1:%.*]] = select <2 x i1> [[CMP1]], <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
+; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[CMP2]], <2 x i8> [[SEL1]], <2 x i8> <i8 20, i8 20>
+; CHECK-NEXT: ret <2 x i8> [[SEL2]]
+;
+ %cmp1 = icmp slt <2 x i8> %x, <i8 10, i8 10>
+ %cmp2 = icmp slt <2 x i8> %x, zeroinitializer
+ %sel1 = select <2 x i1> %cmp1, <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
+ %sel2 = select <2 x i1> %cmp2, <2 x i8> %sel1, <2 x i8> <i8 20, i8 20>
+ ret <2 x i8> %sel2
+}
+
+define i8 @test_implied_true_falseval(i8 %x) {
+; CHECK-LABEL: @test_implied_true_falseval(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X:%.*]], 10
+; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[X]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 20, i8 [[SEL1]]
+; CHECK-NEXT: ret i8 [[SEL2]]
+;
+ %cmp1 = icmp slt i8 %x, 10
+ %cmp2 = icmp sgt i8 %x, 0
+ %sel1 = select i1 %cmp1, i8 0, i8 5
+ %sel2 = select i1 %cmp2, i8 20, i8 %sel1
+ ret i8 %sel2
+}
+
+define i8 @test_implied_false(i8 %x) {
+; CHECK-LABEL: @test_implied_false(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i8 [[X:%.*]], 10
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 [[SEL1]], i8 20
+; CHECK-NEXT: ret i8 [[SEL2]]
+;
+ %cmp1 = icmp sgt i8 %x, 10
+ %cmp2 = icmp slt i8 %x, 0
+ %sel1 = select i1 %cmp1, i8 0, i8 5
+ %sel2 = select i1 %cmp2, i8 %sel1, i8 20
+ ret i8 %sel2
+}
+
+; Negative tests
+
+define i8 @test_imply_fail(i8 %x) {
+; CHECK-LABEL: @test_imply_fail(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X:%.*]], -10
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 [[SEL1]], i8 20
+; CHECK-NEXT: ret i8 [[SEL2]]
+;
+ %cmp1 = icmp slt i8 %x, -10
+ %cmp2 = icmp slt i8 %x, 0
+ %sel1 = select i1 %cmp1, i8 0, i8 5
+ %sel2 = select i1 %cmp2, i8 %sel1, i8 20
+ ret i8 %sel2
+}
+
+define <2 x i8> @test_imply_type_mismatch(<2 x i8> %x, i8 %y) {
+; CHECK-LABEL: @test_imply_type_mismatch(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 10, i8 10>
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[Y:%.*]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select <2 x i1> [[CMP1]], <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], <2 x i8> [[SEL1]], <2 x i8> <i8 20, i8 20>
+; CHECK-NEXT: ret <2 x i8> [[SEL2]]
+;
+ %cmp1 = icmp slt <2 x i8> %x, <i8 10, i8 10>
+ %cmp2 = icmp slt i8 %y, 0
+ %sel1 = select <2 x i1> %cmp1, <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
+ %sel2 = select i1 %cmp2, <2 x i8> %sel1, <2 x i8> <i8 20, i8 20>
+ ret <2 x i8> %sel2
+}
>From 5bfe453202935d883c302045f2ba987a3b318f8b Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 4 Mar 2024 03:25:48 +0800
Subject: [PATCH 2/2] [InstCombine] Simplify nested selects with implied
condition
---
.../InstCombine/InstCombineSelect.cpp | 17 +++++++++++++
...etween-negative-and-positive-thresholds.ll | 12 ++++------
.../Transforms/InstCombine/nested-select.ll | 24 +++++++------------
3 files changed, 29 insertions(+), 24 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 71fa9b9ba41ebb..dc4347fdd713c6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -3867,5 +3867,22 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
}
}
+ // Fold nested selects if the inner condition can be implied by the outer
+ // condition.
+ Value *InnerCondVal;
+ const DataLayout &DL = getDataLayout();
+ if (match(TrueVal,
+ m_Select(m_Value(InnerCondVal), m_Value(LHS), m_Value(RHS))) &&
+ CondVal->getType() == InnerCondVal->getType())
+ if (auto Implied =
+ isImpliedCondition(CondVal, InnerCondVal, DL, /*LHSIsTrue=*/true))
+ return replaceOperand(SI, 1, *Implied ? LHS : RHS);
+ if (match(FalseVal,
+ m_Select(m_Value(InnerCondVal), m_Value(LHS), m_Value(RHS))) &&
+ CondVal->getType() == InnerCondVal->getType())
+ if (auto Implied =
+ isImpliedCondition(CondVal, InnerCondVal, DL, /*LHSIsTrue=*/false))
+ return replaceOperand(SI, 2, *Implied ? LHS : RHS);
+
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/canonicalize-clamp-like-pattern-between-negative-and-positive-thresholds.ll b/llvm/test/Transforms/InstCombine/canonicalize-clamp-like-pattern-between-negative-and-positive-thresholds.ll
index d03e22bc4c9fbf..b5ef1f466958d7 100644
--- a/llvm/test/Transforms/InstCombine/canonicalize-clamp-like-pattern-between-negative-and-positive-thresholds.ll
+++ b/llvm/test/Transforms/InstCombine/canonicalize-clamp-like-pattern-between-negative-and-positive-thresholds.ll
@@ -189,10 +189,8 @@ define i32 @n9_ult_slt_neg17(i32 %x, i32 %replacement_low, i32 %replacement_high
; Regression test for PR53252.
define i32 @n10_ugt_slt(i32 %x, i32 %replacement_low, i32 %replacement_high) {
; CHECK-LABEL: @n10_ugt_slt(
-; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i32 [[REPLACEMENT_LOW:%.*]], i32 [[REPLACEMENT_HIGH:%.*]]
-; CHECK-NEXT: [[T2:%.*]] = icmp ugt i32 [[X]], 128
-; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[X]], i32 [[T1]]
+; CHECK-NEXT: [[T2:%.*]] = icmp ugt i32 [[X:%.*]], 128
+; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[X]], i32 [[REPLACEMENT_HIGH:%.*]]
; CHECK-NEXT: ret i32 [[R]]
;
%t0 = icmp slt i32 %x, 0
@@ -204,10 +202,8 @@ define i32 @n10_ugt_slt(i32 %x, i32 %replacement_low, i32 %replacement_high) {
define i32 @n11_uge_slt(i32 %x, i32 %replacement_low, i32 %replacement_high) {
; CHECK-LABEL: @n11_uge_slt(
-; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i32 [[REPLACEMENT_LOW:%.*]], i32 [[REPLACEMENT_HIGH:%.*]]
-; CHECK-NEXT: [[T2:%.*]] = icmp ult i32 [[X]], 129
-; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[T1]], i32 [[X]]
+; CHECK-NEXT: [[T2:%.*]] = icmp ult i32 [[X:%.*]], 129
+; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[REPLACEMENT_HIGH:%.*]], i32 [[X]]
; CHECK-NEXT: ret i32 [[R]]
;
%t0 = icmp slt i32 %x, 0
diff --git a/llvm/test/Transforms/InstCombine/nested-select.ll b/llvm/test/Transforms/InstCombine/nested-select.ll
index a7cdee1483b46a..d4bbf0ae48590a 100644
--- a/llvm/test/Transforms/InstCombine/nested-select.ll
+++ b/llvm/test/Transforms/InstCombine/nested-select.ll
@@ -501,10 +501,8 @@ define i1 @orcond.111.inv.all.conds(i1 %inner.cond, i1 %alt.cond, i1 %inner.sel.
define i8 @test_implied_true(i8 %x) {
; CHECK-LABEL: @test_implied_true(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X:%.*]], 10
-; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X]], 0
-; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
-; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 [[SEL1]], i8 20
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X:%.*]], 0
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 0, i8 20
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp slt i8 %x, 10
@@ -516,10 +514,8 @@ define i8 @test_implied_true(i8 %x) {
define <2 x i8> @test_implied_true_vec(<2 x i8> %x) {
; CHECK-LABEL: @test_implied_true_vec(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 10, i8 10>
-; CHECK-NEXT: [[CMP2:%.*]] = icmp slt <2 x i8> [[X]], zeroinitializer
-; CHECK-NEXT: [[SEL1:%.*]] = select <2 x i1> [[CMP1]], <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
-; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[CMP2]], <2 x i8> [[SEL1]], <2 x i8> <i8 20, i8 20>
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt <2 x i8> [[X:%.*]], zeroinitializer
+; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[CMP2]], <2 x i8> zeroinitializer, <2 x i8> <i8 20, i8 20>
; CHECK-NEXT: ret <2 x i8> [[SEL2]]
;
%cmp1 = icmp slt <2 x i8> %x, <i8 10, i8 10>
@@ -531,10 +527,8 @@ define <2 x i8> @test_implied_true_vec(<2 x i8> %x) {
define i8 @test_implied_true_falseval(i8 %x) {
; CHECK-LABEL: @test_implied_true_falseval(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X:%.*]], 10
-; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[X]], 0
-; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
-; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 20, i8 [[SEL1]]
+; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[X:%.*]], 0
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 20, i8 0
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp slt i8 %x, 10
@@ -546,10 +540,8 @@ define i8 @test_implied_true_falseval(i8 %x) {
define i8 @test_implied_false(i8 %x) {
; CHECK-LABEL: @test_implied_false(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i8 [[X:%.*]], 10
-; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X]], 0
-; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
-; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 [[SEL1]], i8 20
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X:%.*]], 0
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 5, i8 20
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp sgt i8 %x, 10
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