[llvm] r309415 - [LVI] Constant-propagate a zero extension of the switch condition value through case edges
Hiroshi Yamauchi via llvm-commits
llvm-commits at lists.llvm.org
Fri Jul 28 11:35:25 PDT 2017
Author: yamauchi
Date: Fri Jul 28 11:35:25 2017
New Revision: 309415
URL: http://llvm.org/viewvc/llvm-project?rev=309415&view=rev
Log:
[LVI] Constant-propagate a zero extension of the switch condition value through case edges
Summary:
LazyValueInfo currently computes the constant value of the switch condition through case edges, which allows the constant value to be propagated through the case edges.
But we have seen a case where a zero-extended value of the switch condition is used past case edges for which the constant propagation doesn't occur.
This patch adds a small logic to handle such a case in getEdgeValueLocal().
This is motivated by the Python 2.7 eval loop in PyEval_EvalFrameEx() where the lack of the constant propagation causes longer live ranges and more spill code than necessary.
With this patch, we see that the code size of PyEval_EvalFrameEx() decreases by ~5.4% and a performance test improves by ~4.6%.
Reviewers: wmi, dberlin, sanjoy
Reviewed By: sanjoy
Subscribers: davide, davidxl, llvm-commits
Differential Revision: https://reviews.llvm.org/D34822
Modified:
llvm/trunk/lib/Analysis/LazyValueInfo.cpp
llvm/trunk/test/Transforms/CorrelatedValuePropagation/range.ll
Modified: llvm/trunk/lib/Analysis/LazyValueInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LazyValueInfo.cpp?rev=309415&r1=309414&r2=309415&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/LazyValueInfo.cpp (original)
+++ llvm/trunk/lib/Analysis/LazyValueInfo.cpp Fri Jul 28 11:35:25 2017
@@ -17,6 +17,7 @@
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/AssemblyAnnotationWriter.h"
@@ -148,6 +149,15 @@ public:
return Range;
}
+ Optional<APInt> asConstantInteger() const {
+ if (isConstant() && isa<ConstantInt>(Val)) {
+ return Val->getUniqueInteger();
+ } else if (isConstantRange() && Range.isSingleElement()) {
+ return *Range.getSingleElement();
+ }
+ return Optional<APInt>();
+ }
+
private:
void markOverdefined() {
if (isOverdefined())
@@ -1355,6 +1365,42 @@ LVILatticeVal getValueFromCondition(Valu
return getValueFromCondition(Val, Cond, isTrueDest, Visited);
}
+// Return true if Usr has Op as an operand, otherwise false.
+static bool usesOperand(User *Usr, Value *Op) {
+ return find(Usr->operands(), Op) != Usr->op_end();
+}
+
+// Check if Val can be simplified to an integer constant when the value of one
+// of its operands Op is an integer constant OpConstVal. If so, return it as an
+// lattice value range with a single element or otherwise return an overdefined
+// lattice value.
+static LVILatticeVal constantFoldUser(Value *Val, Value *Op,
+ const APInt &OpConstVal,
+ const DataLayout &DL) {
+ Constant* OpConst = Constant::getIntegerValue(Op->getType(), OpConstVal);
+ // Check if Val can be simplified to a constant.
+ if (auto *CI = dyn_cast<CastInst>(Val)) {
+ assert(CI->getOperand(0) == Op && "Operand 0 isn't Op");
+ if (auto *C = dyn_cast_or_null<ConstantInt>(
+ SimplifyCastInst(CI->getOpcode(), OpConst,
+ CI->getDestTy(), DL))) {
+ return LVILatticeVal::getRange(ConstantRange(C->getUniqueInteger()));
+ }
+ } else if (auto *BO = dyn_cast<BinaryOperator>(Val)) {
+ bool Op0Match = BO->getOperand(0) == Op;
+ bool Op1Match = BO->getOperand(1) == Op;
+ assert((Op0Match || Op1Match) &&
+ "Operand 0 nor Operand 1 isn't a match");
+ Value *LHS = Op0Match ? OpConst : BO->getOperand(0);
+ Value *RHS = Op1Match ? OpConst : BO->getOperand(1);
+ if (auto *C = dyn_cast_or_null<ConstantInt>(
+ SimplifyBinOp(BO->getOpcode(), LHS, RHS, DL))) {
+ return LVILatticeVal::getRange(ConstantRange(C->getUniqueInteger()));
+ }
+ }
+ return LVILatticeVal::getOverdefined();
+}
+
/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge. Result is unspecified if return value
/// is false.
@@ -1370,10 +1416,11 @@ static bool getEdgeValueLocal(Value *Val
bool isTrueDest = BI->getSuccessor(0) == BBTo;
assert(BI->getSuccessor(!isTrueDest) == BBTo &&
"BBTo isn't a successor of BBFrom");
+ Value *Condition = BI->getCondition();
// If V is the condition of the branch itself, then we know exactly what
// it is.
- if (BI->getCondition() == Val) {
+ if (Condition == Val) {
Result = LVILatticeVal::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
return true;
@@ -1381,7 +1428,44 @@ static bool getEdgeValueLocal(Value *Val
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
- Result = getValueFromCondition(Val, BI->getCondition(), isTrueDest);
+ Result = getValueFromCondition(Val, Condition, isTrueDest);
+ if (!Result.isOverdefined())
+ return true;
+
+ if (User *Usr = dyn_cast<User>(Val)) {
+ assert(Result.isOverdefined() && "Result isn't overdefined");
+ if (isa<IntegerType>(Val->getType())) {
+ const DataLayout &DL = BBTo->getModule()->getDataLayout();
+ if (usesOperand(Usr, Condition)) {
+ // If Val has Condition as an operand and Val can be folded into a
+ // constant with either Condition == true or Condition == false,
+ // propagate the constant.
+ // eg.
+ // ; %Val is true on the edge to %then.
+ // %Val = and i1 %Condition, true.
+ // br %Condition, label %then, label %else
+ APInt ConditionVal(1, isTrueDest ? 1 : 0);
+ Result = constantFoldUser(Val, Condition, ConditionVal, DL);
+ } else {
+ // If one of Val's operand has an inferred value, we may be able to
+ // infer the value of Val.
+ // eg.
+ // ; %Val is 94 on the edge to %then.
+ // %Val = add i8 %Op, 1
+ // %Condition = icmp eq i8 %Op, 93
+ // br i1 %Condition, label %then, label %else
+ for (unsigned i = 0; i < Usr->getNumOperands(); ++i) {
+ Value *Op = Usr->getOperand(i);
+ LVILatticeVal OpLatticeVal =
+ getValueFromCondition(Op, Condition, isTrueDest);
+ if (Optional<APInt> OpConst = OpLatticeVal.asConstantInteger()) {
+ Result = constantFoldUser(Val, Op, OpConst.getValue(), DL);
+ break;
+ }
+ }
+ }
+ }
+ }
if (!Result.isOverdefined())
return true;
}
@@ -1390,15 +1474,35 @@ static bool getEdgeValueLocal(Value *Val
// If the edge was formed by a switch on the value, then we may know exactly
// what it is.
if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
- if (SI->getCondition() != Val)
+ Value *Condition = SI->getCondition();
+ if (!isa<IntegerType>(Val->getType()))
return false;
+ bool ValUsesCondition = false;
+ if (Condition != Val) {
+ // Check if Val has Condition as an operand.
+ if (User *Usr = dyn_cast<User>(Val))
+ ValUsesCondition = usesOperand(Usr, Condition);
+ if (!ValUsesCondition)
+ return false;
+ }
+ assert((Condition == Val || ValUsesCondition) &&
+ "Condition != Val nor Val doesn't use Condition");
bool DefaultCase = SI->getDefaultDest() == BBTo;
unsigned BitWidth = Val->getType()->getIntegerBitWidth();
ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
for (auto Case : SI->cases()) {
- ConstantRange EdgeVal(Case.getCaseValue()->getValue());
+ APInt CaseValue = Case.getCaseValue()->getValue();
+ ConstantRange EdgeVal(CaseValue);
+ if (ValUsesCondition) {
+ const DataLayout &DL = BBTo->getModule()->getDataLayout();
+ LVILatticeVal EdgeLatticeVal =
+ constantFoldUser(Val, Condition, CaseValue, DL);
+ if (EdgeLatticeVal.isOverdefined())
+ return false;
+ EdgeVal = EdgeLatticeVal.getConstantRange();
+ }
if (DefaultCase) {
// It is possible that the default destination is the destination of
// some cases. There is no need to perform difference for those cases.
Modified: llvm/trunk/test/Transforms/CorrelatedValuePropagation/range.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CorrelatedValuePropagation/range.ll?rev=309415&r1=309414&r2=309415&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CorrelatedValuePropagation/range.ll (original)
+++ llvm/trunk/test/Transforms/CorrelatedValuePropagation/range.ll Fri Jul 28 11:35:25 2017
@@ -462,3 +462,117 @@ then:
else:
ret i1 false
}
+
+define i32 @test16(i8 %a) {
+entry:
+ %b = zext i8 %a to i32
+ br label %dispatch
+
+dispatch:
+ %cmp = icmp eq i8 %a, 93
+ br i1 %cmp, label %target93, label %dispatch
+
+; CHECK-LABEL: @test16(
+; CHECK: target93:
+; CHECK-NEXT: ret i32 93
+target93:
+ ret i32 %b
+}
+
+define i32 @test16_i1(i1 %a) {
+entry:
+ %b = zext i1 %a to i32
+ br label %dispatch
+
+dispatch:
+ br i1 %a, label %true, label %dispatch
+
+; CHECK-LABEL: @test16_i1(
+; CHECK: true:
+; CHECK-NEXT: ret i32 1
+true:
+ ret i32 %b
+}
+
+define i8 @test17(i8 %a) {
+entry:
+ %c = add i8 %a, 3
+ br label %dispatch
+
+dispatch:
+ %cmp = icmp eq i8 %a, 93
+ br i1 %cmp, label %target93, label %dispatch
+
+; CHECK-LABEL: @test17(
+; CHECK: target93:
+; CHECK-NEXT: ret i8 96
+target93:
+ ret i8 %c
+}
+
+define i8 @test17_2(i8 %a) {
+entry:
+ %c = add i8 %a, %a
+ br label %dispatch
+
+dispatch:
+ %cmp = icmp eq i8 %a, 93
+ br i1 %cmp, label %target93, label %dispatch
+
+; CHECK-LABEL: @test17_2(
+; CHECK: target93:
+; CHECK-NEXT: ret i8 -70
+target93:
+ ret i8 %c
+}
+
+define i1 @test17_i1(i1 %a) {
+entry:
+ %c = and i1 %a, true
+ br label %dispatch
+
+dispatch:
+ br i1 %a, label %true, label %dispatch
+
+; CHECK-LABEL: @test17_i1(
+; CHECK: true:
+; CHECK-NEXT: ret i1 true
+true:
+ ret i1 %c
+}
+
+define i32 @test18(i8 %a) {
+entry:
+ %b = zext i8 %a to i32
+ br label %dispatch
+
+dispatch:
+ switch i8 %a, label %dispatch [
+ i8 93, label %target93
+ i8 -111, label %dispatch
+ ]
+
+; CHECK-LABEL: @test18(
+; CHECK: target93:
+; CHECK-NEXT: ret i32 93
+target93:
+ ret i32 %b
+}
+
+define i8 @test19(i8 %a) {
+entry:
+ %c = add i8 %a, 3
+ br label %dispatch
+
+dispatch:
+ switch i8 %a, label %dispatch [
+ i8 93, label %target93
+ i8 -111, label %dispatch
+ ]
+
+; CHECK-LABEL: @test19(
+; CHECK: target93:
+; CHECK-NEXT: ret i8 96
+target93:
+ ret i8 %c
+}
More information about the llvm-commits
mailing list