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[InstCombine] Simplify binops that are only used by a select and are fed by a select with the same condition. 

Summary:
This patch optimizes a binop sandwiched between 2 selects with the same condition. Since we know its only used by the select we can propagate the appropriate input value from the earlier select.

As I'm writing this I realize I may need to avoid doing this for division in case the select was protecting a divide by zero?

Reviewers: spatel, majnemer

Reviewed By: majnemer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D39999

llvm-svn: 318267
This commit is contained in:
Craig Topper 2017-11-15 05:23:02 +00:00
parent 72a1f98a67
commit f7b86728fa
2 changed files with 92 additions and 0 deletions
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40
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -1643,6 +1643,46 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
}
}
// Try to simplify a binop sandwiched between 2 selects with the same
// condition.
// select(C, binop(select(C, X, Y), W), Z) -> select(C, binop(X, W), Z)
BinaryOperator *TrueBO;
if (match(TrueVal, m_OneUse(m_BinOp(TrueBO)))) {
if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(0))) {
if (TrueBOSI->getCondition() == CondVal) {
TrueBO->setOperand(0, TrueBOSI->getTrueValue());
Worklist.Add(TrueBO);
return &SI;
}
}
if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(1))) {
if (TrueBOSI->getCondition() == CondVal) {
TrueBO->setOperand(1, TrueBOSI->getTrueValue());
Worklist.Add(TrueBO);
return &SI;
}
}
}
// select(C, Z, binop(select(C, X, Y), W)) -> select(C, Z, binop(Y, W))
BinaryOperator *FalseBO;
if (match(FalseVal, m_OneUse(m_BinOp(FalseBO)))) {
if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(0))) {
if (FalseBOSI->getCondition() == CondVal) {
FalseBO->setOperand(0, FalseBOSI->getFalseValue());
Worklist.Add(FalseBO);
return &SI;
}
}
if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(1))) {
if (FalseBOSI->getCondition() == CondVal) {
FalseBO->setOperand(1, FalseBOSI->getFalseValue());
Worklist.Add(FalseBO);
return &SI;
}
}
}
if (BinaryOperator::isNot(CondVal)) {
SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
SI.setOperand(1, FalseVal);

52
llvm/test/Transforms/InstCombine/select.ll
View File

@ -1490,3 +1490,55 @@ entry:
%1 = select <4 x i1> %0, <4 x float> <float 0xFFFFFFFFE0000000, float 0xFFFFFFFFE0000000, float 0xFFFFFFFFE0000000, float 0xFFFFFFFFE0000000>, <4 x float> zeroinitializer
ret <4 x float> %1
}
; select(C, binop(select(C, X, Y), W), Z) -> select(C, binop(X, W), Z)
define i8 @test87(i1 %cond, i8 %w, i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @test87(
; CHECK-NEXT: [[B:%.*]] = add i8 [[X:%.*]], [[W:%.*]]
; CHECK-NEXT: [[C:%.*]] = select i1 [[COND:%.*]], i8 [[B]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[C]]
;
%a = select i1 %cond, i8 %x, i8 %y
%b = add i8 %a, %w
%c = select i1 %cond, i8 %b, i8 %z
ret i8 %c
}
; select(C, binop(select(C, X, Y), W), Z) -> select(C, Z, binop(Y, W))
define i8 @test88(i1 %cond, i8 %w, i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @test88(
; CHECK-NEXT: [[B:%.*]] = sub i8 [[Y:%.*]], [[W:%.*]]
; CHECK-NEXT: [[C:%.*]] = select i1 [[COND:%.*]], i8 [[Z:%.*]], i8 [[B]]
; CHECK-NEXT: ret i8 [[C]]
;
%a = select i1 %cond, i8 %x, i8 %y
%b = sub i8 %a, %w
%c = select i1 %cond, i8 %z, i8 %b
ret i8 %c
}
; select(C, Z, binop(W, select(C, X, Y))) -> select(C, binop(X, W), Z)
define i8 @test89(i1 %cond, i8 %w, i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @test89(
; CHECK-NEXT: [[B:%.*]] = and i8 [[X:%.*]], [[W:%.*]]
; CHECK-NEXT: [[C:%.*]] = select i1 [[COND:%.*]], i8 [[B]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[C]]
;
%a = select i1 %cond, i8 %x, i8 %y
%b = and i8 %w, %a
%c = select i1 %cond, i8 %b, i8 %z
ret i8 %c
}
; select(C, Z, binop(W, select(C, X, Y))) -> select(C, Z, binop(W, Y))
define i8 @test90(i1 %cond, i8 %w, i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @test90(
; CHECK-NEXT: [[B:%.*]] = or i8 [[Y:%.*]], [[W:%.*]]
; CHECK-NEXT: [[C:%.*]] = select i1 [[COND:%.*]], i8 [[Z:%.*]], i8 [[B]]
; CHECK-NEXT: ret i8 [[C]]
;
%a = select i1 %cond, i8 %x, i8 %y
%b = or i8 %w, %a
%c = select i1 %cond, i8 %z, i8 %b
ret i8 %c
}