[llvm] [SCEVExpander] Recognize urem idiom during expansion (PR #96005)
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 19 08:39:53 PDT 2024
https://github.com/preames updated https://github.com/llvm/llvm-project/pull/96005
>From f616e477ad6408329aae4badc176d39ad033c7c4 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Tue, 18 Jun 2024 13:24:08 -0700
Subject: [PATCH 1/2] [SCEVExpander] Recognize urem idiom during expansion
If we have a urem expression, emitting it as a urem is significantly better
that letting the fully expansion kick in. We have the risk of a udiv or
mul which could have previously been shared, but loosing that seems like
a reasonable tradeoff for being able to round trip a urem w/o modification.
---
llvm/lib/Analysis/ScalarEvolution.cpp | 4 ++++
llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp | 11 +++++++++++
.../X86/postinc-iv-used-by-urem-and-udiv.ll | 8 ++------
.../trip-count-expansion-may-introduce-ub.ll | 4 +---
4 files changed, 18 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 9808308cbfed9..03c51d86f891d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -14972,6 +14972,10 @@ void PredicatedScalarEvolution::print(raw_ostream &OS, unsigned Depth) const {
// 4, A / B becomes X / 8).
bool ScalarEvolution::matchURem(const SCEV *Expr, const SCEV *&LHS,
const SCEV *&RHS) {
+
+ if (Expr->getType()->isPointerTy())
+ return false;
+
// Try to match 'zext (trunc A to iB) to iY', which is used
// for URem with constant power-of-2 second operands. Make sure the size of
// the operand A matches the size of the whole expressions.
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index c437a44dda8d3..32b2127f5fc5e 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -491,6 +491,17 @@ class LoopCompare {
}
Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
+
+ // Recognize the canonical representation of an unsimplifed urem.
+ const SCEV *URemLHS = nullptr;
+ const SCEV *URemRHS = nullptr;
+ if (SE.matchURem(S, URemLHS, URemRHS)) {
+ Value *LHS = expand(URemLHS);
+ Value *RHS = expand(URemRHS);
+ return InsertBinop(Instruction::URem, LHS, RHS, SCEV::FlagAnyWrap,
+ /*IsSafeToHoist*/ false);
+ }
+
// Collect all the add operands in a loop, along with their associated loops.
// Iterate in reverse so that constants are emitted last, all else equal, and
// so that pointer operands are inserted first, which the code below relies on
diff --git a/llvm/test/Transforms/LoopStrengthReduce/X86/postinc-iv-used-by-urem-and-udiv.ll b/llvm/test/Transforms/LoopStrengthReduce/X86/postinc-iv-used-by-urem-and-udiv.ll
index 95b064bd044fa..838b48aa56906 100644
--- a/llvm/test/Transforms/LoopStrengthReduce/X86/postinc-iv-used-by-urem-and-udiv.ll
+++ b/llvm/test/Transforms/LoopStrengthReduce/X86/postinc-iv-used-by-urem-and-udiv.ll
@@ -22,9 +22,7 @@ define i32 @test_pr38847() {
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[LSR]], -1
; CHECK-NEXT: br i1 [[CMP2]], label [[LOOP]], label [[EXIT:%.*]]
; CHECK: exit:
-; CHECK-NEXT: [[TMP0:%.*]] = udiv i32 [[LSR_IV_NEXT2]], 9
-; CHECK-NEXT: [[TMP1:%.*]] = mul nuw i32 [[TMP0]], 9
-; CHECK-NEXT: [[TMP2:%.*]] = sub i32 [[LSR_IV_NEXT2]], [[TMP1]]
+; CHECK-NEXT: [[TMP2:%.*]] = urem i32 [[LSR_IV_NEXT2]], 9
; CHECK-NEXT: ret i32 [[TMP2]]
;
entry:
@@ -109,9 +107,7 @@ define i32 @test_pr62852() {
; CHECK: exit:
; CHECK-NEXT: call void @use(i64 [[LSR_IV_NEXT]])
; CHECK-NEXT: call void @use(i64 [[LSR_IV_NEXT2]])
-; CHECK-NEXT: [[TMP1:%.*]] = udiv i32 [[DEC_1]], 53
-; CHECK-NEXT: [[TMP2:%.*]] = mul nuw i32 [[TMP1]], 53
-; CHECK-NEXT: [[TMP3:%.*]] = sub i32 [[DEC_1]], [[TMP2]]
+; CHECK-NEXT: [[TMP3:%.*]] = urem i32 [[DEC_1]], 53
; CHECK-NEXT: ret i32 [[TMP3]]
;
entry:
diff --git a/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll b/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
index ce5d4427fa019..bf687a31d8d17 100644
--- a/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
+++ b/llvm/test/Transforms/LoopVectorize/trip-count-expansion-may-introduce-ub.ll
@@ -723,9 +723,7 @@ define i64 @multi_exit_4_exit_count_with_urem_by_constant_in_latch(ptr %dst, i64
; CHECK-SAME: ptr [[DST:%.*]], i64 [[N:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[N]], i64 0)
-; CHECK-NEXT: [[TMP0:%.*]] = udiv i64 [[N]], 42
-; CHECK-NEXT: [[TMP1:%.*]] = mul nuw i64 [[TMP0]], 42
-; CHECK-NEXT: [[TMP2:%.*]] = sub i64 [[N]], [[TMP1]]
+; CHECK-NEXT: [[TMP2:%.*]] = urem i64 [[N]], 42
; CHECK-NEXT: [[SMAX1:%.*]] = call i64 @llvm.smax.i64(i64 [[TMP2]], i64 0)
; CHECK-NEXT: [[UMIN:%.*]] = call i64 @llvm.umin.i64(i64 [[SMAX]], i64 [[SMAX1]])
; CHECK-NEXT: [[TMP3:%.*]] = add nuw i64 [[UMIN]], 1
>From d454434b9302842b31b44c43f836143b861f6f25 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Wed, 19 Jun 2024 08:37:50 -0700
Subject: [PATCH 2/2] Address review comments
---
llvm/lib/Analysis/ScalarEvolution.cpp | 1 -
llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp | 1 -
2 files changed, 2 deletions(-)
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 03c51d86f891d..7fb7074269024 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -14972,7 +14972,6 @@ void PredicatedScalarEvolution::print(raw_ostream &OS, unsigned Depth) const {
// 4, A / B becomes X / 8).
bool ScalarEvolution::matchURem(const SCEV *Expr, const SCEV *&LHS,
const SCEV *&RHS) {
-
if (Expr->getType()->isPointerTy())
return false;
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 32b2127f5fc5e..c7d758aa575e6 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -491,7 +491,6 @@ class LoopCompare {
}
Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
-
// Recognize the canonical representation of an unsimplifed urem.
const SCEV *URemLHS = nullptr;
const SCEV *URemRHS = nullptr;
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