[llvm] 400ceda - [SCEV][IndVars] Always provide insertion point to the SCEVExpander::isHighCostExpansion()
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 25 12:07:23 PST 2020
Author: Roman Lebedev
Date: 2020-02-25T23:05:59+03:00
New Revision: 400ceda425ab392096ff2800acad41a4322974d2
URL: https://github.com/llvm/llvm-project/commit/400ceda425ab392096ff2800acad41a4322974d2
DIFF: https://github.com/llvm/llvm-project/commit/400ceda425ab392096ff2800acad41a4322974d2.diff
LOG: [SCEV][IndVars] Always provide insertion point to the SCEVExpander::isHighCostExpansion()
Summary: This addresses the `llvm/test/Transforms/IndVarSimplify/elim-extend.ll` `@nestedIV` regression from D73728
Reviewers: reames, mkazantsev, wmi, sanjoy
Reviewed By: mkazantsev
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73777
Added:
Modified:
llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
llvm/lib/Analysis/ScalarEvolutionExpander.cpp
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
llvm/test/Transforms/IndVarSimplify/elim-extend.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h b/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
index 720d0a3718f9..7a94f6320a56 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
@@ -176,18 +176,19 @@ namespace llvm {
/// Return true for expressions that can't be evaluated at runtime
/// within given \b Budget.
///
- /// At is an optional parameter which specifies point in code where user is
- /// going to expand this expression. Sometimes this knowledge can lead to a
- /// more accurate cost estimation.
+ /// At is a parameter which specifies point in code where user is going to
+ /// expand this expression. Sometimes this knowledge can lead to
+ /// a less pessimistic cost estimation.
bool isHighCostExpansion(const SCEV *Expr, Loop *L, unsigned Budget,
const TargetTransformInfo *TTI,
- const Instruction *At = nullptr) {
+ const Instruction *At) {
assert(TTI && "This function requires TTI to be provided.");
+ assert(At && "This function requires At instruction to be provided.");
if (!TTI) // In assert-less builds, avoid crashing
return true; // by always claiming to be high-cost.
SmallPtrSet<const SCEV *, 8> Processed;
int BudgetRemaining = Budget * TargetTransformInfo::TCC_Basic;
- return isHighCostExpansionHelper(Expr, L, At, BudgetRemaining, *TTI,
+ return isHighCostExpansionHelper(Expr, L, *At, BudgetRemaining, *TTI,
Processed);
}
@@ -331,7 +332,7 @@ namespace llvm {
/// Recursive helper function for isHighCostExpansion.
bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
- const Instruction *At, int &BudgetRemaining,
+ const Instruction &At, int &BudgetRemaining,
const TargetTransformInfo &TTI,
SmallPtrSetImpl<const SCEV *> &Processed);
diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index 65a88ea25c70..a09f1f3b6cea 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2136,7 +2136,7 @@ SCEVExpander::getRelatedExistingExpansion(const SCEV *S, const Instruction *At,
}
bool SCEVExpander::isHighCostExpansionHelper(
- const SCEV *S, Loop *L, const Instruction *At, int &BudgetRemaining,
+ const SCEV *S, Loop *L, const Instruction &At, int &BudgetRemaining,
const TargetTransformInfo &TTI, SmallPtrSetImpl<const SCEV *> &Processed) {
if (BudgetRemaining < 0)
return true; // Already run out of budget, give up.
@@ -2147,7 +2147,7 @@ bool SCEVExpander::isHighCostExpansionHelper(
// If we can find an existing value for this scev available at the point "At"
// then consider the expression cheap.
- if (At && getRelatedExistingExpansion(S, At, L))
+ if (getRelatedExistingExpansion(S, &At, L))
return false; // Consider the expression to be free.
switch (S->getSCEVType()) {
@@ -2198,18 +2198,12 @@ bool SCEVExpander::isHighCostExpansionHelper(
// UDiv from the user's code. If we can't find a UDiv in the code with some
// simple searching, we need to account for it's cost.
- BasicBlock *ExitingBB = L->getExitingBlock();
- if (At || ExitingBB) {
- if (!At)
- At = &ExitingBB->back();
-
- // At the beginning of this function we already tried to find existing
- // value for plain 'S'. Now try to lookup 'S + 1' since it is common
- // pattern involving division. This is just a simple search heuristic.
- if (getRelatedExistingExpansion(
- SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), At, L))
- return false; // Consider it to be free.
- }
+ // At the beginning of this function we already tried to find existing
+ // value for plain 'S'. Now try to lookup 'S + 1' since it is common
+ // pattern involving division. This is just a simple search heuristic.
+ if (getRelatedExistingExpansion(
+ SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), &At, L))
+ return false; // Consider it to be free.
// Need to count the cost of this UDiv.
BudgetRemaining -= TTI.getOperationCost(Instruction::UDiv, S->getType());
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index e513070201e5..b8a4705d06c8 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2726,6 +2726,9 @@ bool IndVarSimplify::run(Loop *L) {
// If we have a trip count expression, rewrite the loop's exit condition
// using it.
if (!DisableLFTR) {
+ BasicBlock *PreHeader = L->getLoopPreheader();
+ BranchInst *PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator());
+
SmallVector<BasicBlock*, 16> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
for (BasicBlock *ExitingBB : ExitingBlocks) {
@@ -2760,7 +2763,7 @@ bool IndVarSimplify::run(Loop *L) {
// Avoid high cost expansions. Note: This heuristic is questionable in
// that our definition of "high cost" is not exactly principled.
if (Rewriter.isHighCostExpansion(ExitCount, L, SCEVCheapExpansionBudget,
- TTI))
+ TTI, PreHeaderBR))
continue;
// Check preconditions for proper SCEVExpander operation. SCEV does not
diff --git a/llvm/test/Transforms/IndVarSimplify/elim-extend.ll b/llvm/test/Transforms/IndVarSimplify/elim-extend.ll
index 7e245933c331..3387cfa9bbbd 100644
--- a/llvm/test/Transforms/IndVarSimplify/elim-extend.ll
+++ b/llvm/test/Transforms/IndVarSimplify/elim-extend.ll
@@ -140,8 +140,8 @@ define void @nestedIV(i8* %address, i32 %limit) nounwind {
; CHECK-NEXT: store i8 0, i8* [[ADR2]]
; CHECK-NEXT: [[ADR3:%.*]] = getelementptr i8, i8* [[ADDRESS]], i64 [[INDVARS_IV_NEXT]]
; CHECK-NEXT: store i8 0, i8* [[ADR3]]
-; CHECK-NEXT: [[INNERCMP:%.*]] = icmp sgt i64 [[TMP0]], [[INDVARS_IV_NEXT]]
-; CHECK-NEXT: br i1 [[INNERCMP]], label [[INNERLOOP]], label [[INNEREXIT:%.*]]
+; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[TMP0]]
+; CHECK-NEXT: br i1 [[EXITCOND]], label [[INNERLOOP]], label [[INNEREXIT:%.*]]
; CHECK: innerexit:
; CHECK-NEXT: [[TMP4:%.*]] = trunc i64 [[TMP0]] to i32
; CHECK-NEXT: br label [[OUTERMERGE]]
@@ -153,8 +153,8 @@ define void @nestedIV(i8* %address, i32 %limit) nounwind {
; CHECK-NEXT: [[ADR5:%.*]] = getelementptr i8, i8* [[ADDRESS]], i64 [[OFS5]]
; CHECK-NEXT: store i8 0, i8* [[ADR5]]
; CHECK-NEXT: [[INDVARS_IV_NEXT2]] = add nuw nsw i64 [[INDVARS_IV1]], 1
-; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT2]], [[WIDE_TRIP_COUNT]]
-; CHECK-NEXT: br i1 [[EXITCOND]], label [[OUTERLOOP]], label [[RETURN:%.*]]
+; CHECK-NEXT: [[EXITCOND4:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT2]], [[WIDE_TRIP_COUNT]]
+; CHECK-NEXT: br i1 [[EXITCOND4]], label [[OUTERLOOP]], label [[RETURN:%.*]]
; CHECK: return:
; CHECK-NEXT: ret void
;
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