[llvm] 2bf3fe9 - [TRE] Allow elimination when the returned value is non-constant
Eli Friedman via llvm-commits
llvm-commits at lists.llvm.org
Wed May 27 16:55:30 PDT 2020
Author: Layton Kifer
Date: 2020-05-27T16:55:03-07:00
New Revision: 2bf3fe9b6dedf727990e68244a3d637518ea8bc3
URL: https://github.com/llvm/llvm-project/commit/2bf3fe9b6dedf727990e68244a3d637518ea8bc3
DIFF: https://github.com/llvm/llvm-project/commit/2bf3fe9b6dedf727990e68244a3d637518ea8bc3.diff
LOG: [TRE] Allow elimination when the returned value is non-constant
Currently we can only eliminate call return pairs that either return the
result of the call or a dynamic constant. This patch removes that
limitation.
Differential Revision: https://reviews.llvm.org/D79660
Added:
Modified:
llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
llvm/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll
llvm/test/Transforms/TailCallElim/basic.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp b/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
index 4fd63fa1838b..a752e356b727 100644
--- a/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -460,6 +460,16 @@ class TailRecursionEliminator {
SmallVector<PHINode *, 8> ArgumentPHIs;
bool RemovableCallsMustBeMarkedTail = false;
+ // PHI node to store our return value.
+ PHINode *RetPN = nullptr;
+
+ // i1 PHI node to track if we have a valid return value stored in RetPN.
+ PHINode *RetKnownPN = nullptr;
+
+ // Vector of select instructions we insereted. These selects use RetKnownPN
+ // to either propagate RetPN or select a new return value.
+ SmallVector<SelectInst *, 8> RetSelects;
+
TailRecursionEliminator(Function &F, const TargetTransformInfo *TTI,
AliasAnalysis *AA, OptimizationRemarkEmitter *ORE,
DomTreeUpdater &DTU)
@@ -577,6 +587,21 @@ void TailRecursionEliminator::createTailRecurseLoopHeader(CallInst *CI) {
PN->addIncoming(&*I, NewEntry);
ArgumentPHIs.push_back(PN);
}
+
+ // If the function doen't return void, create the RetPN and RetKnownPN PHI
+ // nodes to track our return value. We initialize RetPN with undef and
+ // RetKnownPN with false since we can't know our return value at function
+ // entry.
+ Type *RetType = F.getReturnType();
+ if (!RetType->isVoidTy()) {
+ Type *BoolType = Type::getInt1Ty(F.getContext());
+ RetPN = PHINode::Create(RetType, 2, "ret.tr", InsertPos);
+ RetKnownPN = PHINode::Create(BoolType, 2, "ret.known.tr", InsertPos);
+
+ RetPN->addIncoming(UndefValue::get(RetType), NewEntry);
+ RetKnownPN->addIncoming(ConstantInt::getFalse(BoolType), NewEntry);
+ }
+
// The entry block was changed from HeaderBB to NewEntry.
// The forward DominatorTree needs to be recalculated when the EntryBB is
// changed. In this corner-case we recalculate the entire tree.
@@ -616,11 +641,7 @@ bool TailRecursionEliminator::eliminateCall(CallInst *CI) {
// value for the accumulator is placed in this variable. If this value is set
// then we actually perform accumulator recursion elimination instead of
// simple tail recursion elimination. If the operation is an LLVM instruction
- // (eg: "add") then it is recorded in AccumulatorRecursionInstr. If not, then
- // we are handling the case when the return instruction returns a constant C
- // which is
diff erent to the constant returned by other return instructions
- // (which is recorded in AccumulatorRecursionEliminationInitVal). This is a
- // special case of accumulator recursion, the operation being "return C".
+ // (eg: "add") then it is recorded in AccumulatorRecursionInstr.
Value *AccumulatorRecursionEliminationInitVal = nullptr;
Instruction *AccumulatorRecursionInstr = nullptr;
@@ -647,26 +668,6 @@ bool TailRecursionEliminator::eliminateCall(CallInst *CI) {
}
}
- // We can only transform call/return pairs that either ignore the return value
- // of the call and return void, ignore the value of the call and return a
- // constant, return the value returned by the tail call, or that are being
- // accumulator recursion variable eliminated.
- if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI &&
- !isa<UndefValue>(Ret->getReturnValue()) &&
- AccumulatorRecursionEliminationInitVal == nullptr &&
- !getCommonReturnValue(nullptr, CI)) {
- // One case remains that we are able to handle: the current return
- // instruction returns a constant, and all other return instructions
- // return a
diff erent constant.
- if (!isDynamicConstant(Ret->getReturnValue(), CI, Ret))
- return false; // Current return instruction does not return a constant.
- // Check that all other return instructions return a common constant. If
- // so, record it in AccumulatorRecursionEliminationInitVal.
- AccumulatorRecursionEliminationInitVal = getCommonReturnValue(Ret, CI);
- if (!AccumulatorRecursionEliminationInitVal)
- return false;
- }
-
BasicBlock *BB = Ret->getParent();
using namespace ore;
@@ -698,20 +699,15 @@ bool TailRecursionEliminator::eliminateCall(CallInst *CI) {
PHINode *AccPN = insertAccumulator(AccumulatorRecursionEliminationInitVal);
Instruction *AccRecInstr = AccumulatorRecursionInstr;
- if (AccRecInstr) {
- // Add an incoming argument for the current block, which is computed by
- // our associative and commutative accumulator instruction.
- AccPN->addIncoming(AccRecInstr, BB);
-
- // Next, rewrite the accumulator recursion instruction so that it does not
- // use the result of the call anymore, instead, use the PHI node we just
- // inserted.
- AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
- } else {
- // Add an incoming argument for the current block, which is just the
- // constant returned by the current return instruction.
- AccPN->addIncoming(Ret->getReturnValue(), BB);
- }
+
+ // Add an incoming argument for the current block, which is computed by
+ // our associative and commutative accumulator instruction.
+ AccPN->addIncoming(AccRecInstr, BB);
+
+ // Next, rewrite the accumulator recursion instruction so that it does not
+ // use the result of the call anymore, instead, use the PHI node we just
+ // inserted.
+ AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
// Finally, rewrite any return instructions in the program to return the PHI
// node instead of the "initval" that they do currently. This loop will
@@ -722,6 +718,25 @@ bool TailRecursionEliminator::eliminateCall(CallInst *CI) {
++NumAccumAdded;
}
+ // Update our return value tracking
+ if (RetPN) {
+ if (Ret->getReturnValue() == CI || AccumulatorRecursionEliminationInitVal) {
+ // Defer selecting a return value
+ RetPN->addIncoming(RetPN, BB);
+ RetKnownPN->addIncoming(RetKnownPN, BB);
+ } else {
+ // We found a return value we want to use, insert a select instruction to
+ // select it if we don't already know what our return value will be and
+ // store the result in our return value PHI node.
+ SelectInst *SI = SelectInst::Create(
+ RetKnownPN, RetPN, Ret->getReturnValue(), "current.ret.tr", Ret);
+ RetSelects.push_back(SI);
+
+ RetPN->addIncoming(SI, BB);
+ RetKnownPN->addIncoming(ConstantInt::getTrue(RetKnownPN->getType()), BB);
+ }
+ }
+
// Now that all of the PHI nodes are in place, remove the call and
// ret instructions, replacing them with an unconditional branch.
BranchInst *NewBI = BranchInst::Create(HeaderBB, Ret);
@@ -804,6 +819,30 @@ void TailRecursionEliminator::cleanupAndFinalize() {
PN->eraseFromParent();
}
}
+
+ if (RetPN) {
+ if (RetSelects.empty()) {
+ // If we didn't insert any select instructions, then we know we didn't
+ // store a return value and we can remove the PHI nodes we inserted.
+ RetPN->dropAllReferences();
+ RetPN->eraseFromParent();
+
+ RetKnownPN->dropAllReferences();
+ RetKnownPN->eraseFromParent();
+ } else {
+ // We need to insert a select instruction before any return left in the
+ // function to select our stored return value if we have one.
+ for (BasicBlock &BB : F) {
+ ReturnInst *RI = dyn_cast<ReturnInst>(BB.getTerminator());
+ if (!RI)
+ continue;
+
+ SelectInst *SI = SelectInst::Create(
+ RetKnownPN, RetPN, RI->getOperand(0), "current.ret.tr", RI);
+ RI->setOperand(0, SI);
+ }
+ }
+ }
}
bool TailRecursionEliminator::eliminate(Function &F,
diff --git a/llvm/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll b/llvm/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll
index 48110e3283cf..4e0346c14c34 100644
--- a/llvm/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll
+++ b/llvm/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll
@@ -1,20 +1,112 @@
; RUN: opt < %s -tailcallelim -verify-dom-info -S | FileCheck %s
; PR7328
; PR7506
-define i32 @foo(i32 %x) {
-; CHECK-LABEL: define i32 @foo(
-; CHECK: %accumulator.tr = phi i32 [ 1, %entry ], [ 0, %body ]
+define i32 @test1_constants(i32 %x) {
entry:
%cond = icmp ugt i32 %x, 0 ; <i1> [#uses=1]
br i1 %cond, label %return, label %body
body: ; preds = %entry
%y = add i32 %x, 1 ; <i32> [#uses=1]
- %tmp = call i32 @foo(i32 %y) ; <i32> [#uses=0]
-; CHECK-NOT: call
+ %recurse = call i32 @test1_constants(i32 %y) ; <i32> [#uses=0]
ret i32 0
-; CHECK: ret i32 %accumulator.tr
return: ; preds = %entry
ret i32 1
}
+
+; CHECK-LABEL: define i32 @test1_constants(
+; CHECK: tailrecurse:
+; CHECK: %ret.tr = phi i32 [ undef, %entry ], [ %current.ret.tr, %body ]
+; CHECK: %ret.known.tr = phi i1 [ false, %entry ], [ true, %body ]
+; CHECK: body:
+; CHECK-NOT: %recurse
+; CHECK: %current.ret.tr = select i1 %ret.known.tr, i32 %ret.tr, i32 0
+; CHECK-NOT: ret
+; CHECK: return:
+; CHECK: %current.ret.tr1 = select i1 %ret.known.tr, i32 %ret.tr, i32 1
+; CHECK: ret i32 %current.ret.tr1
+
+define i32 @test2_non_constants(i32 %x) {
+entry:
+ %cond = icmp ugt i32 %x, 0
+ br i1 %cond, label %return, label %body
+
+body:
+ %y = add i32 %x, 1
+ %helper1 = call i32 @test2_helper()
+ %recurse = call i32 @test2_non_constants(i32 %y)
+ ret i32 %helper1
+
+return:
+ %helper2 = call i32 @test2_helper()
+ ret i32 %helper2
+}
+
+declare i32 @test2_helper()
+
+; CHECK-LABEL: define i32 @test2_non_constants(
+; CHECK: tailrecurse:
+; CHECK: %ret.tr = phi i32 [ undef, %entry ], [ %current.ret.tr, %body ]
+; CHECK: %ret.known.tr = phi i1 [ false, %entry ], [ true, %body ]
+; CHECK: body:
+; CHECK-NOT: %recurse
+; CHECK: %current.ret.tr = select i1 %ret.known.tr, i32 %ret.tr, i32 %helper1
+; CHECK-NOT: ret
+; CHECK: return:
+; CHECK: %current.ret.tr1 = select i1 %ret.known.tr, i32 %ret.tr, i32 %helper2
+; CHECK: ret i32 %current.ret.tr1
+
+define i32 @test3_mixed(i32 %x) {
+entry:
+ switch i32 %x, label %default [
+ i32 0, label %case0
+ i32 1, label %case1
+ i32 2, label %case2
+ ]
+
+case0:
+ %helper1 = call i32 @test3_helper()
+ br label %return
+
+case1:
+ %y1 = add i32 %x, -1
+ %recurse1 = call i32 @test3_mixed(i32 %y1)
+ br label %return
+
+case2:
+ %y2 = add i32 %x, -1
+ %helper2 = call i32 @test3_helper()
+ %recurse2 = call i32 @test3_mixed(i32 %y2)
+ br label %return
+
+default:
+ %y3 = urem i32 %x, 3
+ %recurse3 = call i32 @test3_mixed(i32 %y3)
+ br label %return
+
+return:
+ %retval = phi i32 [ %recurse3, %default ], [ %helper2, %case2 ], [ 9, %case1 ], [ %helper1, %case0 ]
+ ret i32 %retval
+}
+
+declare i32 @test3_helper()
+
+; CHECK-LABEL: define i32 @test3_mixed(
+; CHECK: tailrecurse:
+; CHECK: %ret.tr = phi i32 [ undef, %entry ], [ %current.ret.tr, %case1 ], [ %current.ret.tr1, %case2 ], [ %ret.tr, %default ]
+; CHECK: %ret.known.tr = phi i1 [ false, %entry ], [ true, %case1 ], [ true, %case2 ], [ %ret.known.tr, %default ]
+; CHECK: case1:
+; CHECK-NOT: %recurse
+; CHECK: %current.ret.tr = select i1 %ret.known.tr, i32 %ret.tr, i32 9
+; CHECK: br label %tailrecurse
+; CHECK: case2:
+; CHECK-NOT: %recurse
+; CHECK: %current.ret.tr1 = select i1 %ret.known.tr, i32 %ret.tr, i32 %helper2
+; CHECK: br label %tailrecurse
+; CHECK: default:
+; CHECK-NOT: %recurse
+; CHECK: br label %tailrecurse
+; CHECK: return:
+; CHECK: %current.ret.tr2 = select i1 %ret.known.tr, i32 %ret.tr, i32 %helper1
+; CHECK: ret i32 %current.ret.tr2
diff --git a/llvm/test/Transforms/TailCallElim/basic.ll b/llvm/test/Transforms/TailCallElim/basic.ll
index 576f2fec1244..6116014a024b 100644
--- a/llvm/test/Transforms/TailCallElim/basic.ll
+++ b/llvm/test/Transforms/TailCallElim/basic.ll
@@ -46,8 +46,16 @@ endif.0: ; preds = %entry
; plunked it into the demo script, so maybe they care about it.
define i32 @test3(i32 %c) {
; CHECK: i32 @test3
+; CHECK: tailrecurse:
+; CHECK: %ret.tr = phi i32 [ undef, %entry ], [ %current.ret.tr, %else ]
+; CHECK: %ret.known.tr = phi i1 [ false, %entry ], [ true, %else ]
+; CHECK: else:
; CHECK-NOT: call
-; CHECK: ret i32 0
+; CHECK: %current.ret.tr = select i1 %ret.known.tr, i32 %ret.tr, i32 0
+; CHECK-NOT: ret
+; CHECK: return:
+; CHECK: %current.ret.tr1 = select i1 %ret.known.tr, i32 %ret.tr, i32 0
+; CHECK: ret i32 %current.ret.tr1
entry:
%tmp.1 = icmp eq i32 %c, 0 ; <i1> [#uses=1]
br i1 %tmp.1, label %return, label %else
More information about the llvm-commits
mailing list