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[InstCombine] Fold more select of selects using isImpliedCondition 

This is a simple folding that does these:

```
select x_inv, true, (select y, x, false)
=>
select x_inv, true, y
```
https://alive2.llvm.org/ce/z/-STJ2d

```
select (select y, x, false), true, x_inv
=>
select y, true, x_inv
```
https://alive2.llvm.org/ce/z/6ruYt6

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D101807
This commit is contained in:
Juneyoung Lee 2021-05-04 10:16:21 +09:00
parent a71d666d18
commit 1fef5c88a6
2 changed files with 19 additions and 8 deletions
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15
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -2773,6 +2773,21 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
if (Res && *Res == false)
return replaceOperand(SI, 1, A);
}
// select c, true, (select a, b, false) -> select c, true, a
// select (select a, b, false), true, c -> select a, true, c
// if c = false implies that b = true
if (match(TrueVal, m_One()) &&
match(FalseVal, m_Select(m_Value(A), m_Value(B), m_Zero()))) {
Optional<bool> Res = isImpliedCondition(CondVal, B, DL, false);
if (Res && *Res == true)
return replaceOperand(SI, 2, A);
}
if (match(CondVal, m_Select(m_Value(A), m_Value(B), m_Zero())) &&
match(TrueVal, m_One())) {
Optional<bool> Res = isImpliedCondition(FalseVal, B, DL, false);
if (Res && *Res == true)
return replaceOperand(SI, 0, A);
}
// sel (sel c, a, false), true, (sel !c, b, false) -> sel c, a, b
// sel (sel !c, a, false), true, (sel c, b, false) -> sel c, b, a

12
llvm/test/Transforms/InstCombine/select-safe-transforms.ll
View File

@ -181,10 +181,8 @@ define i1 @bools2_logical(i1 %a, i1 %b, i1 %c) {
define i1 @orn_and_cmp_1_logical(i37 %a, i37 %b, i1 %y) {
; CHECK-LABEL: @orn_and_cmp_1_logical(
; CHECK-NEXT: [[X:%.*]] = icmp sgt i37 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[X_INV:%.*]] = icmp sle i37 [[A]], [[B]]
; CHECK-NEXT: [[AND:%.*]] = select i1 [[Y:%.*]], i1 [[X]], i1 false
; CHECK-NEXT: [[OR:%.*]] = select i1 [[X_INV]], i1 true, i1 [[AND]]
; CHECK-NEXT: [[X_INV:%.*]] = icmp sle i37 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[OR:%.*]] = select i1 [[X_INV]], i1 true, i1 [[Y:%.*]]
; CHECK-NEXT: ret i1 [[OR]]
;
%x = icmp sgt i37 %a, %b
@ -196,10 +194,8 @@ define i1 @orn_and_cmp_1_logical(i37 %a, i37 %b, i1 %y) {
define i1 @orn_and_cmp_2_logical(i16 %a, i16 %b, i1 %y) {
; CHECK-LABEL: @orn_and_cmp_2_logical(
; CHECK-NEXT: [[X:%.*]] = icmp sge i16 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[X_INV:%.*]] = icmp slt i16 [[A]], [[B]]
; CHECK-NEXT: [[AND:%.*]] = select i1 [[Y:%.*]], i1 [[X]], i1 false
; CHECK-NEXT: [[OR:%.*]] = select i1 [[AND]], i1 true, i1 [[X_INV]]
; CHECK-NEXT: [[X_INV:%.*]] = icmp slt i16 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[OR:%.*]] = select i1 [[Y:%.*]], i1 true, i1 [[X_INV]]
; CHECK-NEXT: ret i1 [[OR]]
;
%x = icmp sge i16 %a, %b