[llvm] [SimplifyCFG] Add support for sinking instructions with multiple uses (PR #95521)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Fri Jun 14 06:27:10 PDT 2024
https://github.com/nikic updated https://github.com/llvm/llvm-project/pull/95521
>From 1465062a97ac77b4ea170ebed024183dc822c3a8 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Tue, 4 Jun 2024 17:09:00 +0200
Subject: [PATCH 1/2] [SimplifyCFG] Add support for sinking instructions with
multiple uses
Sinking currently only supports instructions that have zero or one
uses. Extend this to handle instructions with any number of uses,
as long as all uses are consistent (i.e. the "same" for all
sinking candidates).
After #94462 this is basically just a matter of looping over all
uses instead of checking the first one only.
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 22 ++++-----
.../SimplifyCFG/X86/sink-common-code.ll | 46 +++++++------------
2 files changed, 26 insertions(+), 42 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 9c7f90b0613a0..85d774d20daa0 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1936,7 +1936,7 @@ static bool canSinkInstructions(
// Prune out obviously bad instructions to move. Each instruction must have
// exactly zero or one use, and we check later that use is by a single, common
// PHI instruction in the successor.
- bool HasUse = !Insts.front()->user_empty();
+ std::optional<unsigned> NumUses;
for (auto *I : Insts) {
// These instructions may change or break semantics if moved.
if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
@@ -1956,10 +1956,9 @@ static bool canSinkInstructions(
if (C->isInlineAsm() || C->cannotMerge() || C->isConvergent())
return false;
- // Each instruction must have zero or one use.
- if (HasUse && !I->hasOneUse())
- return false;
- if (!HasUse && !I->user_empty())
+ if (!NumUses)
+ NumUses = I->getNumUses();
+ else if (NumUses != I->getNumUses())
return false;
}
@@ -1987,8 +1986,7 @@ static bool canSinkInstructions(
// then the other phi operands must match the instructions from Insts. This
// also has to hold true for any phi nodes that would be created as a result
// of sinking. Both of these cases are represented by PhiOperands.
- if (HasUse) {
- const Use &U = *I0->use_begin();
+ for (const Use &U : I0->uses()) {
auto It = PHIOperands.find(&U);
if (It == PHIOperands.end())
// There may be uses in other blocks when sinking into a loop header.
@@ -2138,11 +2136,11 @@ static void sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
I0->andIRFlags(I);
}
- if (!I0->user_empty()) {
- // canSinkLastInstruction checked that all instructions were used by
- // one and only one PHI node. Find that now, RAUW it to our common
- // instruction and nuke it.
- auto *PN = cast<PHINode>(*I0->user_begin());
+ for (User *U : make_early_inc_range(I0->users())) {
+ // canSinkLastInstruction checked that all instructions are only used by
+ // phi nodes a way that allows replacing the phi node with the common
+ // instruction.
+ auto *PN = cast<PHINode>(U);
PN->replaceAllUsesWith(I0);
PN->eraseFromParent();
}
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
index 7b2161351a794..be2f17dc1c780 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
@@ -1704,19 +1704,14 @@ return:
define ptr @multi_use_in_phi(i1 %cond, ptr %p, i64 %a, i64 %b) {
; CHECK-LABEL: @multi_use_in_phi(
-; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
+; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[JOIN:%.*]]
; CHECK: if:
; CHECK-NEXT: call void @dummy()
-; CHECK-NEXT: [[GEP1_A:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
-; CHECK-NEXT: br label [[JOIN:%.*]]
-; CHECK: else:
-; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P]], i64 [[A]]
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
-; CHECK-NEXT: [[GEP1_B_SINK:%.*]] = phi ptr [ [[GEP1_B]], [[ELSE]] ], [ [[GEP1_A]], [[IF]] ]
-; CHECK-NEXT: [[PHI1:%.*]] = phi ptr [ [[GEP1_A]], [[IF]] ], [ [[GEP1_B]], [[ELSE]] ]
-; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B_SINK]], i64 [[B:%.*]]
-; CHECK-NEXT: call void @use.ptr(ptr [[PHI1]])
+; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
+; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[B:%.*]]
+; CHECK-NEXT: call void @use.ptr(ptr [[GEP1_B]])
; CHECK-NEXT: ret ptr [[GEP2_B]]
;
br i1 %cond, label %if, label %else
@@ -1778,23 +1773,16 @@ join:
define i64 @multi_use_in_block(i1 %cond, ptr %p, i64 %a, i64 %b) {
; CHECK-LABEL: @multi_use_in_block(
-; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
+; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[JOIN:%.*]]
; CHECK: if:
; CHECK-NEXT: call void @dummy()
-; CHECK-NEXT: [[GEP1_A:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
-; CHECK-NEXT: [[V_A:%.*]] = load i64, ptr [[GEP1_A]], align 8
-; CHECK-NEXT: [[GEP2_A:%.*]] = getelementptr i8, ptr [[GEP1_A]], i64 [[V_A]]
-; CHECK-NEXT: br label [[JOIN:%.*]]
-; CHECK: else:
-; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P]], i64 [[A]]
-; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[GEP1_B]], align 8
-; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[V_B]]
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
-; CHECK-NEXT: [[PHI1:%.*]] = phi i64 [ [[V_A]], [[IF]] ], [ [[V_B]], [[ELSE]] ]
-; CHECK-NEXT: [[PHI2:%.*]] = phi ptr [ [[GEP2_A]], [[IF]] ], [ [[GEP2_B]], [[ELSE]] ]
-; CHECK-NEXT: call void @use.ptr(ptr [[PHI2]])
-; CHECK-NEXT: ret i64 [[PHI1]]
+; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
+; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[GEP1_B]], align 8
+; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[V_B]]
+; CHECK-NEXT: call void @use.ptr(ptr [[GEP2_B]])
+; CHECK-NEXT: ret i64 [[V_B]]
;
br i1 %cond, label %if, label %else
@@ -1824,19 +1812,17 @@ define i64 @multi_use_in_block_inconsistent(i1 %cond, ptr %p, i64 %a, i64 %b) {
; CHECK: if:
; CHECK-NEXT: call void @dummy()
; CHECK-NEXT: [[GEP1_A:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
-; CHECK-NEXT: [[V_A:%.*]] = load i64, ptr [[GEP1_A]], align 8
-; CHECK-NEXT: [[GEP2_A:%.*]] = getelementptr i8, ptr [[GEP1_A]], i64 [[V_A]]
; CHECK-NEXT: br label [[JOIN:%.*]]
; CHECK: else:
; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P]], i64 [[A]]
-; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[P]], align 8
-; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[V_B]]
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
-; CHECK-NEXT: [[PHI1:%.*]] = phi i64 [ [[V_A]], [[IF]] ], [ [[V_B]], [[ELSE]] ]
-; CHECK-NEXT: [[PHI2:%.*]] = phi ptr [ [[GEP2_A]], [[IF]] ], [ [[GEP2_B]], [[ELSE]] ]
-; CHECK-NEXT: call void @use.ptr(ptr [[PHI2]])
-; CHECK-NEXT: ret i64 [[PHI1]]
+; CHECK-NEXT: [[P_SINK:%.*]] = phi ptr [ [[P]], [[ELSE]] ], [ [[GEP1_A]], [[IF]] ]
+; CHECK-NEXT: [[GEP1_B_SINK:%.*]] = phi ptr [ [[GEP1_B]], [[ELSE]] ], [ [[GEP1_A]], [[IF]] ]
+; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[P_SINK]], align 8
+; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B_SINK]], i64 [[V_B]]
+; CHECK-NEXT: call void @use.ptr(ptr [[GEP2_B]])
+; CHECK-NEXT: ret i64 [[V_B]]
;
br i1 %cond, label %if, label %else
>From d92d3e8d53facbde718e0effd75a407c4e891e31 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Fri, 14 Jun 2024 15:26:39 +0200
Subject: [PATCH 2/2] comment fixes
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 85d774d20daa0..69ea00e53724f 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1934,8 +1934,7 @@ static bool canSinkInstructions(
ArrayRef<Instruction *> Insts,
DenseMap<const Use *, SmallVector<Value *, 4>> &PHIOperands) {
// Prune out obviously bad instructions to move. Each instruction must have
- // exactly zero or one use, and we check later that use is by a single, common
- // PHI instruction in the successor.
+ // the same number of uses, and we check later that the uses are consistent.
std::optional<unsigned> NumUses;
for (auto *I : Insts) {
// These instructions may change or break semantics if moved.
@@ -2138,7 +2137,7 @@ static void sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
for (User *U : make_early_inc_range(I0->users())) {
// canSinkLastInstruction checked that all instructions are only used by
- // phi nodes a way that allows replacing the phi node with the common
+ // phi nodes in a way that allows replacing the phi node with the common
// instruction.
auto *PN = cast<PHINode>(U);
PN->replaceAllUsesWith(I0);
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