[llvm] goldsteinn/simplify cfg expensive divrem by var (PR #109007)
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Tue Sep 17 09:05:19 PDT 2024
https://github.com/goldsteinn created https://github.com/llvm/llvm-project/pull/109007
- **[SimplifyCFG] Add test for sinking div/rem with const remainder; NFC**
- **[SimplifyCFG] Mark div/rem as not-cheap to sink if we are replacing const denominator**
>From a2b771475ed7fff38f230b77787006ab2aba824f Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Tue, 17 Sep 2024 00:06:25 -0500
Subject: [PATCH 1/2] [SimplifyCFG] Add test for sinking div/rem with const
remainder; NFC
---
.../SimplifyCFG/sink-and-convert-switch.ll | 82 +++++++++++++++++++
1 file changed, 82 insertions(+)
diff --git a/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll b/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll
index 4c93837f1422a9..bb24fdd04e5741 100644
--- a/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll
+++ b/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll
@@ -44,3 +44,85 @@ bb5:
call void @llvm.lifetime.end.p0(i64 1, ptr nonnull %y)
ret void
}
+
+define i64 @dont_make_div_variable(i64 noundef %x, i64 noundef %i) {
+; CHECK-LABEL: define i64 @dont_make_div_variable(
+; CHECK-SAME: i64 noundef [[X:%.*]], i64 noundef [[I:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub nsw i64 [[I]], 9
+; CHECK-NEXT: [[SWITCH_OFFSET:%.*]] = add nsw i64 [[SWITCH_TABLEIDX]], 9
+; CHECK-NEXT: [[DIV6:%.*]] = udiv i64 [[X]], [[SWITCH_OFFSET]]
+; CHECK-NEXT: ret i64 [[DIV6]]
+;
+entry:
+ switch i64 %i, label %sw.default [
+ i64 9, label %sw.bb
+ i64 10, label %sw.bb1
+ i64 11, label %sw.bb3
+ i64 12, label %sw.bb5
+ ]
+
+sw.bb:
+ %div = udiv i64 %x, 9
+ br label %return
+
+sw.bb1:
+ %div2 = udiv i64 %x, 10
+ br label %return
+
+sw.bb3:
+ %div4 = udiv i64 %x, 11
+ br label %return
+
+sw.bb5:
+ %div6 = udiv i64 %x, 12
+ br label %return
+
+sw.default:
+ unreachable
+
+return:
+ %retval.0 = phi i64 [ %div6, %sw.bb5 ], [ %div4, %sw.bb3 ], [ %div2, %sw.bb1 ], [ %div, %sw.bb ]
+ ret i64 %retval.0
+}
+
+define i64 @okay_to_make_div_variable(i64 noundef %x, i64 noundef %i) {
+; CHECK-LABEL: define i64 @okay_to_make_div_variable(
+; CHECK-SAME: i64 noundef [[X:%.*]], i64 noundef [[I:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub nsw i64 [[I]], 9
+; CHECK-NEXT: [[SWITCH_OFFSET:%.*]] = add nsw i64 [[SWITCH_TABLEIDX]], 9
+; CHECK-NEXT: [[DIV6:%.*]] = udiv i64 [[SWITCH_OFFSET]], [[X]]
+; CHECK-NEXT: ret i64 [[DIV6]]
+;
+entry:
+ switch i64 %i, label %sw.default [
+ i64 9, label %sw.bb
+ i64 10, label %sw.bb1
+ i64 11, label %sw.bb3
+ i64 12, label %sw.bb5
+ ]
+
+sw.bb:
+ %div = udiv i64 9, %x
+ br label %return
+
+sw.bb1:
+ %div2 = udiv i64 10, %x
+ br label %return
+
+sw.bb3:
+ %div4 = udiv i64 11, %x
+ br label %return
+
+sw.bb5:
+ %div6 = udiv i64 12, %x
+ br label %return
+
+sw.default:
+ unreachable
+
+return:
+ %retval.0 = phi i64 [ %div6, %sw.bb5 ], [ %div4, %sw.bb3 ], [ %div2, %sw.bb1 ], [ %div, %sw.bb ]
+ ret i64 %retval.0
+}
>From aa52aff554601ac3185bbf58c2c06f9913a83cc0 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Tue, 17 Sep 2024 00:06:28 -0500
Subject: [PATCH 2/2] [SimplifyCFG] Mark div/rem as not-cheap to sink if we are
replacing const denominator
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 10 ++++++++
.../SimplifyCFG/sink-and-convert-switch.ll | 25 ++++++++++++++++---
2 files changed, 32 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 5a694b5e7f204b..5e08d4d3ffe7f8 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1954,6 +1954,16 @@ static bool isLifeTimeMarker(const Instruction *I) {
// into variables.
static bool replacingOperandWithVariableIsCheap(const Instruction *I,
int OpIdx) {
+ switch (I->getOpcode()) {
+ // Divide/Remainder by constant is typically much cheaper than by variable.
+ case Instruction::UDiv:
+ case Instruction::SDiv:
+ case Instruction::URem:
+ case Instruction::SRem:
+ return OpIdx != 1;
+ default:
+ break;
+ }
return !isa<IntrinsicInst>(I);
}
diff --git a/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll b/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll
index bb24fdd04e5741..87d64932ef0935 100644
--- a/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll
+++ b/llvm/test/Transforms/SimplifyCFG/sink-and-convert-switch.ll
@@ -49,9 +49,28 @@ define i64 @dont_make_div_variable(i64 noundef %x, i64 noundef %i) {
; CHECK-LABEL: define i64 @dont_make_div_variable(
; CHECK-SAME: i64 noundef [[X:%.*]], i64 noundef [[I:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
-; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub nsw i64 [[I]], 9
-; CHECK-NEXT: [[SWITCH_OFFSET:%.*]] = add nsw i64 [[SWITCH_TABLEIDX]], 9
-; CHECK-NEXT: [[DIV6:%.*]] = udiv i64 [[X]], [[SWITCH_OFFSET]]
+; CHECK-NEXT: switch i64 [[I]], label %[[SW_DEFAULT:.*]] [
+; CHECK-NEXT: i64 9, label %[[SW_BB:.*]]
+; CHECK-NEXT: i64 10, label %[[SW_BB1:.*]]
+; CHECK-NEXT: i64 11, label %[[SW_BB3:.*]]
+; CHECK-NEXT: i64 12, label %[[SW_BB5:.*]]
+; CHECK-NEXT: ]
+; CHECK: [[SW_BB]]:
+; CHECK-NEXT: [[DIV:%.*]] = udiv i64 [[X]], 9
+; CHECK-NEXT: br label %[[RETURN:.*]]
+; CHECK: [[SW_BB1]]:
+; CHECK-NEXT: [[DIV2:%.*]] = udiv i64 [[X]], 10
+; CHECK-NEXT: br label %[[RETURN]]
+; CHECK: [[SW_BB3]]:
+; CHECK-NEXT: [[DIV4:%.*]] = udiv i64 [[X]], 11
+; CHECK-NEXT: br label %[[RETURN]]
+; CHECK: [[SW_BB5]]:
+; CHECK-NEXT: [[DIV7:%.*]] = udiv i64 [[X]], 12
+; CHECK-NEXT: br label %[[RETURN]]
+; CHECK: [[SW_DEFAULT]]:
+; CHECK-NEXT: unreachable
+; CHECK: [[RETURN]]:
+; CHECK-NEXT: [[DIV6:%.*]] = phi i64 [ [[DIV7]], %[[SW_BB5]] ], [ [[DIV4]], %[[SW_BB3]] ], [ [[DIV2]], %[[SW_BB1]] ], [ [[DIV]], %[[SW_BB]] ]
; CHECK-NEXT: ret i64 [[DIV6]]
;
entry:
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